result and discussion - information and library...

RESULT AND DISCUSSION

110

5. Mefenamic acid ......................................................................................................111

5.1. Mefenamic acid Spherical crystallization ...........................................................111

5.1.1 Selection of the best liquid proportions ............................................................111

5.1.2 Influence of the various bridging liquids ..........................................................113

5.1.3 Influence of bridging liquid on particle size: ....................................................113

5.1.5 Optimum stirring time or residence time ..........................................................118

5.1.6 Influence of the temperature .............................................................................118

5.1.7 Influence of mode of addition of bridging liquid..............................................118

5.2 Recrystallization of Mefenamic acid: ..................................................................120

5.3 Crystallization by spray drying technique: ..........................................................120

5.4 Crystallization by freeze drying techniques:........................................................122

5.5 Super cooling crystallization (solidification technique): .....................................123

5.6 Characterization of Mefenamic acid spherical agglomerates ..............................123

5.6.1 Percentage yield: ...............................................................................................123

5.6.2 Drug content......................................................................................................124

5.6.3 Melting point:....................................................................................................124

5.6.4 Water content ....................................................................................................125

5.6.5 Residual solvent content: ..................................................................................125

5.6.6 Differential scanning calorimetry (DSC) ..........................................................126

5.6.7 FT-IR Spectroscopy: .........................................................................................129

5.6.8 X-ray analysis: ..................................................................................................132

5.6.9 Surface topography by scanning electron microscopy (SEM): ........................143

5.7 Evaluation of prepared crystals: ...........................................................................146

5.7.1 Micromeritic properties: ...................................................................................146

5.7.2 Mechanical properties: ......................................................................................149

5.7.3 Solubility studies:..............................................................................................154

5.7.4 Dissolution behaviour of crystals: ....................................................................156

5.7.5 Various parameters of model fittings of Mefenamic acid samples...................159

5.7.6 Stability study: ..................................................................................................161

5.8 Preparation of conventional tablet: ......................................................................162

5.8.1 Evaluation of Mefenamic acid tablets: .............................................................162

5.8.2 Dissolution studies of tablets: ...........................................................................162


111

5. Mefenamic acid

5.1. Mefenamic acid Spherical crystallization

A typical spherical crystallization solvent system involved a good solvent, a

poor solvent for a drug and a bridging liquid. The selection of these solvents depends

on the miscibility of the solvents and solubility of the drug in individual solvents.

Mefenamic acid is freely soluble in Tetra hydro furan (THF). It is necessary to select

a solvent in which Mefenamic acid exhibits the maximum solubility. In fact, a very

concentrated solution of drug could increase the densification of the material during

the crystallization process. The addition of bridging liquid (isopropyl acetate)

promotes the transfer of the drug to a third emulsified phase in which crystal

agglomerates densify and grows spherically164, 165

. Moreover, Tetrahydrofuran (THF)

is miscible in all proportion with water and isopropyl acetate.

5.1.1 Selection of the best liquid proportions

Mefenamic acid soluble in Tetrahydrofuran, ethanol, methanol, isopropyl

acetate and chloroform. Based upon high volatility, high viscosity and low reactivity

of THF and isopropyl acetate were determined to be a suitable crystallization solvent.

Mefenamic acid showed high solubility in THF (1.75gm/10ml). Hence, THF used as

good solvent.

If the ternary diagram is envisaged, isopropyl acetate and water are like an

emulsion in a large of area of this diagram. To select the best solvent composition, a

ternary diagram was constructed. The points on the vertex correspond to a pure liquid;

those on the sides correspond to a mixture of only two liquids. Since the presence of

three liquids is necessary (good solvent, bridging solvent and poor solvent) for

spherical crystallization, points on the sides of the triangle are excluded. 36 points


112

remain for experiments. Each triangle in the ternary diagram was investigated for the

crystallization. The optimal ratio for spherical crystallization is found in zone Figure

20. These proportions of THF/water/ isopropyl acetate were finally chosen for the

study166

.

Mefenamic acid is also soluble in isopropyl acetate, Isopropyl acetate is also

soluble in THF and capable of forming liquid bridges between the particles of

mefenamic acid.

Figure 20: Ternary diagram of Mefenamic acid – THF/water/ isopropyl acetate.

To optimize Mefenamic acid spherical crystallization by THF/water/ isopropyl

acetate system, several parameters were considered; among these are, influence of

bridging liquid, influence of the rotation speed, influence of the temperature,

influence of mode of addition of bridging liquid and stirring time164, 166

.


113

5.1.2 Influence of the various bridging liquids

Among Isopropyl acetate, chloroform and toluene, which were used as

bridging liquids, Isopropyl acetate and chloroform produced spherical crystals.

However spherical crystals formed using Isopropyl acetate showed improved

micromeritic properties, solubility and dissolution properties compared to spherical

agglomerates produced by chloroform. Hence Isopropyl acetate was selected as a

bridging liquid for spherical crystallization of Mefenamic acid165, 168

.

5.1.3 Influence of bridging liquid on particle size:

The influence of the composition of the good solvent, poor solvent and

bridging liquid in the system on the particle size of spherically agglomerated crystals

were investigated164, 168

. The solvent composition was varied with respect to isopropyl

acetate and water in the crystallization medium, with the amount of THF being

constant.

The average size of agglomerated crystals increased with increasing amount of

Isopropyl acetate due to enhanced agglomeration of crystals. The excess bridging

liquid on the surface of crystals allowed greater coalescence of crystals. When 9 ml of

isopropyl acetate was used crystals were small, brittle due to lack of enough bridging

liquid. With further increase in isopropyl acetate amount (11 ml), lumps were

obtained. Hence the 10 ml of bridging liquid was selected for the preparation of

spherical agglomerates of Mefenamic acid (Table 9, 10 & Figure 21).


114

Table 9 Amount of solvents selected from phase diagram used to prepare

spherical crystals of Mefenamic acid

Amount (ml) of

tetrahydrofuran

(good solvent)

Amount (ml) of

Water used in

ml (poor

solvent)

Amount (ml) of

Isopropyl acetate used

in ml (bridging liquid)

Percent of

bridging liquid

20 71 9 9

20 70 10 10

20 69 11 11

Table 10 Effect of volume of bridging liquid on size distribution of spherical

crystals

Particle diameter (µm)

Percentage Frequency

9 ml 10ml 11 ml

500 11.32 8.14 6.05

710 19.44 16.12 8.72

1000 30.5 25.85 15.44

1200 38.78 29.37 24.89

1450 29.14 24.65 35.09

1700 6.23 9.17 8.65


115

Figure 21 Effect of volume of bridging liquid on size distribution of Spherical

crystals

0

5

10

15

20

25

30

35

40

45

0 200 400 600 800 1000 1200 1400 1600 1800

% F

req

uen

cy


9 ml 10 ml 11 ml


116

5.1.4 Influence of the rotation speed of the stirring

Different stirring rates were studied as they influence the secondary characters

of spherical crystals. Solvent composition (THF: Isopropyl acetate: water) of

crystallization medium was kept constant, different stirring rates 300±25, 400±25,

500±25, 600±25 and 700±25 rpm were used (164, 168). The movement of droplets

within the medium induces circulation inside the droplets. The intensity of this

internal circulation depends on the speed. Higher speed induces crystal agglomerate

destruction (600±25 & 700±25). A lower stirring rate reduces the possibility of

obtaining spherical crystals (300±25 & 400±25). Size distributions of particles at

various degrees of agitation are shown in the Figure 22 & Table 11. The size of

agglomerates was very much dependent on the degree of agitation. For a constant

period of stirring, as the speed of agitation is increased, the size of agglomerates

obtained was decreased. This may be due to the fact that as the speed of agitation

increases the impact energy for collision of particle increases due to increased

turbulence, resulting in agglomerates, which are more compact and dense. Hence

500±25 rpm was selected for the preparation of spherical agglomerates of the

Mefenamic acid.

Particle size distribution was narrow at 600 rmp, while 400 rpm and 500 rpm

produced agglomerates of broad distribution.


117

Table 11 Effect of intensity agitation on size distribution of spherical crystals


Percentage frequency

600rpm 500rpm 400rpm

500 7.87 7.52 5.88

710 23.86 13.47 8.75

1000 44.73 22.75 14.34

1200 13.83 28.24 24.21

1450 2.13 22.06 40.53

1700 - 2.57 5.41

Figure 22 Effect of intensity of agitation on size distribution of Spherical

agglomerates.

0

5

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1000 1200 1400 1600 1800

% F

req

uen

cy

Particle diameter (µm

600 rmp 500 rmp 400 rmp


118

5.1.5 Optimum stirring time or residence time

Optimum stirring time or residence time for which the spherical crystals

remain suspended in the crystallization medium was found to be 25±5 min. Spherical

crystals did not form when the stirring time was below 25 min. due to incomplete

crystallization/agglomeration. Longer residence time resulted in breakdown of

spherical crystals or may be surface could have rough due to secondary crystallization

164,168.

5.1.6 Influence of the temperature

The temperature of agglomerating solvents was found to have pronounced

effect on the process of spherical crystallization. Agglomeration and hence formation

of crystal agglomerates could not occur when the process was carried out at 2±5oC. It

could be due to reduced solubility of drug in crystallization solvents at such a lower

temperature, which did not affect efficient wetting of drug particles and hence

reduced agglomeration. When the temperature of the process was increased to 45±5oC

very large agglomerates were produced and the amount of the recovery of the drug

was reduced. It could be due to increased solubility of the drug at this higher

temperature. Optimum agglomeration was obtained when the process was carried out

at 25±5oC

164, 165, 168.

5.1.7 Influence of mode of addition of bridging liquid

Uniform distribution of bridging liquid was obtained when it was added drop

wise with continuous stirring of agitator. This process resulted in the formation of

spherical crystals due to efficient crystallization. Pouring of whole amount of bridging

liquid in crystallization vessel at a time produced spherical crystals of irregular


119

geometry. It is due to localization of bridging liquid and hence its unavailability for

efficient crystallization164, 165, 168

.

Table 12 Effect of variables on formulation of spherical crystals of Mefenamic

acid

Parameter

Variables

Observation

Bridging liquid

IPA

Chloroform

Toluene

Agglomeration

Agglomeration

No agglomeration

Percentage (%) of

bridging liquid Isopropyl

acetate

9%

10%

11%

No agglomeration

Agglomeration

No agglomeration

Agitation speed

300±25

400±25

500±25

600±25

700±25

Clumps

Spherical & large

Spherical

Spherical & small

Irregular shape & small

Agitation time

˂45 min

45 min

Incomplete agglomerates

Spherical agglomerates

Temperature

5±20 C

20±20C

45±20 C

Large Spherical Agglomerates

Spherical agglomeration

no agglomerates

Mode of addition of

bridging liquid

Whole at a time

Drop wise

Crystals of irregular geometry

Spherical agglomerates


120

5.2 Recrystallization of Mefenamic acid:

Recrystallization of Mefenamic acid was done to find out the changes in crystal

lattice, being induced by solvents that can influence the some physicochemical

properties and secondary characteristics of the drug substance. Hence the mechanical,

micromeritic and dissolution properties of prepared crystals were compared with

commercial sample of mefenamic acid168

.

5.3 Crystallization by spray drying technique:

The spray technology being applied to the manufacture of mefenamic acid crystals

using the same solvent system as used in spherical crystallization. In this technique,

energy is applied to the droplet, forcing evaporation of the medium resulting in both

energy and mass transfer through the droplet. Spray drying is the most widely used

industrial process involving crystals formation and drying. It is highly suited for the

continuous production of dry crystals of mefenamic acid169, 173

.

In spray drying method, three important parameters were considered, 1. Inlet

temperature 2. Feed rate/ flow rate of drug solids in the solution and 3. Atomization

pressure rate/ atomization speed rotation. All three parameter have an impact on the

yield of spray dried crystals. Process variables are summarized in Table 13.


121

Table 13 Influence of process variables on crystals of Spray dried crystals of

Mefenamic acid

Parameter Variables Observation

Inlet Temperature

100±20 C

110±20 C

120±20 C

Less % yield

Complete dry crystals with high yield

Less % yield

Feed rate/ flow rate of

drug solids in the solution

10%

12%

15%

Less % yield, Irregular shape crystals

Good % yield, Spherical shape crystals

Sticking to wall, Less % yield, Irregular

shape crystals

Atomization pressure

rate/ Atomization speed

rotation

0.5 kg/cm2

1 kg/cm2

2 kg/cm2

Incomplete crystals, Less % yield

Complete spherical crystals, good %

yield

Sticking to wall, Irregular shape

crystals, Less % yield


122

5.4 Crystallization by freeze drying techniques:

While optimizing the Freeze-drying process, three parameter were considered;

Time of freezing, Time of primary drying, Time of secondary drying. Process

variables are summarized in Table 14.

Table 14 Influence of process variables on crystals of freeze dried crystals of

Mefenamic acid

Sl.

No. Parameter Variables Observation

1. Time of freezing

-30 0C for 12 hr

-40 0C for 24 hr

-50 0C for 36 h

Incomplete solidification

Complete solidification

Complete f solidification but over

frozen product

2. Time of primary

drying

48 hr

72 hr

96 hr

Incomplete dried sample

Complete dried sample with good

properties

Complete dried sample with higher

water content

3. Time of

secondary drying

18 hr

24 hr

36 hr

Complete dried sample with higher

water content

Complete dried sample with good

properties

Complete dried sample with poor

properties

Optimized parameters of the Freeze-drying process have been selected as

follow: Time of freezing: -40 0C for 24 hr, Time of primary drying: 72 hr, Time of

secondary drying: 24 hr170, 197, 198

.


123

5.5 Super cooling crystallization (solidification technique):

In this method Mefenamic acid was heated until it is melted. The melt is solidified

rapidly in an ice bath under rigorous stirring, pulverized, and then sieved. Rapid

congealing is desirable because it results in super saturation of drug. Crystals from

this process can be obtained in pellet form without the necessity of a grinding step

that may alter crystalline modification171, 172, 173

.

The super-cooling process could be considered as a self-seed process in which

the nucleus occurs. The super-cooling process significantly reduce the nucleation time

and increase the overall crystallization rate which result in a higher crystallinity than

that in other crystallization techniques.

5.6 Characterization of Mefenamic acid spherical agglomerates

5.6.1 Percentage yield:

The yield was in the range of 78-95%. The yield of crystals prepared by different

crystallization techniques is presented Table 15:

Table 15 Yield of different crystals of mefenamic acid by different crystallization

techniques

Sl. No. Different crystals % yields*

1 Spherical crystals 78± 2

2 Spray dried crystals 79± 2

3 Freeze dried crystals 86± 2

4 Super cooling crystals 78± 2

5 Recrystallized crystals 95± 2

*Mean SD± n=5

Yield was less for the drug crystallized by spherical crystallization, spray drying,

freeze drying and super cooling. some loss, resulting from transferring solids from

one container to another and leaving a little material behind. Also, because of the

finite solubility of the solid in the crystallization solvent, even at low temperatures,


124

any unnecessary prolonged contact with crystallization solvent, especially if the

solvent is not ice-cold will result in loss of product. Some of the product would have

redissolved and lost. During spherical crystallization, particles were sticking to the

wall of container and stirrer, while in case of spray drying, inability of the cyclone

separator to trap particles smaller than 2 μm and adherence of these particles to the

inner wall of the spray drier174, 175

. For super cooling crystals, drugs particles were

sticking to the wall of the container which led to the loss in yield.

5.6.2 Drug content

Drug content in various crystals prepared is presented Table 16.

Table 16 Drug content of different crystals of mefenamic acid

Sl. No. Different crystals Drug content*

1 Spherical crystals 98.43± 0.3

2 Spray dried crystals 99.12± 0.2

3 Freeze dried crystals 99.89± 0.1

4 Super cooling crystals 13.56 ± 2.5

5 Recrystallized crystals 98.67± 0.2

*Mean SD± n=5

5.6.3 Melting point:

Melting point of Mefenamic acid was determined by capillary filled method. The

Melting point of crystals prepared by different crystallization techniques are shown in

Table 17.

Table 17: Melting point of different crystals of Mefenamic acid

Sl. No. Mefenamic acid

crystals

Literature melting point

(20)

Observed melting

point

1 Commercial sample

229-2310C

231±0.5

2 Spherical crystals 230±0.5

3 Spray dried crystals 229±0.5

4 Freeze dried crystals 229±0.5

5 Super cooling crystals 233±0.5

6 Recrystallized crystals 231±0.5


125

5.6.4 Water content

This test is important in cases where the drug, like mefenamic acid, is known to be

hygroscopic or degraded by moisture or when the drug substance is known to be a

stoichiometric hydrate. A Loss on drying due to water evaporation may be considered

adequate in some cases, ICH guidelines specify that the water content shall essentially

be determined by Karl Fischer titration176

. The water content in crystals prepared by

different crystallization techniques are shown in Table 18.

Table 18: Water contain of different crystals of mefenamic acid

Sl. No. Mefenamic acid crystals Water content (% w/w)

1 Commercial sample 4.56

2 Spherical crystals 4.34

3 Spray dried crystals 4.47

4 Freeze dried crystals 5.32

5 Super cooling crystals 4.71

6 Recrystallized crystals 4.92

Not More than: 5 % w/w (39).

5.6.5 Residual solvent content:

THF and isopropyl acetate are considered as toxic organic solvent based on its

concentration, however these little detriment to human body. According to the

International Conference on Harmonization (ICH) guidelines for residual solvents, the

solvents are classified into three different categories: Class I, II and III solvents, Class

I solvents are extremely toxic, class II are moderately toxic and class III are low toxic.

Although not listed in the ICH guidelines, THF and isopropyl acetate are fall in the

category of a class II and class III respectively. Therefore, the low level of THF and

isopropyl acetate in the crystals should not be harmful to both animal and human177,

178.

Residual solvents in prepared crystals were determined (THF and isopropyl acetate)

by Gas chromatography presented in Table 19.


126

Table 19 Residual solvent in different crystals of Mefenamic acid

Sl. No. Solvents ICH Class and

limit (ppm)

Mefenamic acid

crystals

Residual solvent

(ppm)

1 Isopropyl

acetate

Class 3

5000 ppm

Spherical crystals

Spray dried crystals

Freeze dried crystals

Recrystallized crystals

07

10

11

09

2 Tetrahydrofuran

Class 2

720 ppm

Spherical crystals

Spray dried crystals

Freeze dried crystals

Recrystallized crystals

14

15

18

15

5.6.6 Differential scanning calorimetry (DSC)

DSC studies were performed for different crystals of Mefenamic acid. The

DSC thermograms of Mefenamic acid commercial sample, spherical agglomerates,

spray dried crystals, freeze dried crystals, super cooling crystals and recrystallized

sample are presented in Figure 23. Onset of melt (T0), melting point (Tm) and

completion of melt (Tc) is present in the Table 20. The DSC thermograms show a

sharp endothermic peak for all the Mefenamic acid crystals except super cooling

crystals. This one step melt might be due to only one crystal form (Triclinic) of the

Mefenamic acid formed during the crystallization process. Thus indicating that

Mefenamic acid did not undergo any crystal modification. The temperatures of the

endothermic peaks of all the Mefenamic acid crystals were in the range of 2290C to

2330C. Melting point of the mefenamic acid was 231.32 with enthalpy 184.3 J/g

183.

Melting points show slight variation as the solvent might have affected the nature of

the crystals, the melting points determined by open capillaries are agreement with

DSC studies. The thermogram of super cooling crystals showed at three peaks at

2230C, 241

0C and 272

0C respectively with different enthalpy indicating change in the

polymorphic form of the mefenamic acid.


127

The prepared crystals have decreased in crystallinity & Heat of fusion than

commercial sample of mefenamic acid. The crystallinity was in the following order

FD>SD>SA>RS>CS. The decreased crystallinity and Heat of fusion of the different

crystals of Mefenamic acid may be one of the reasons for enhanced solubility and

dissolution of the prepared crystals196

.

The melting point and enthalpy for prepared crystals of mefenamic acid are presented

in Table 20.

Table 20 DSC data of different Mefenamic acid crystals

Crystals T0 Tm Tc Melting range Heat of fusion*

J/gm

Decreased %

crystallinity

Commercia

l sample 225.14 231.32 234.73 9.59 184.32 J/g 100

Spherical

crystals 226.23 230.17 234.63 8.40 167.64 J/g 90.95

Spray dried

crystals 225.02 229.71 233.42 8.40 159.19 J/g 86.36

Freeze

dried

crystals

226.52 229.56 233.58 7.06 145.53 J/g 78.95

Recrystalliz

ed sample 227.43 233.01 234.65 7.22 177.41 J/g 96.25

Super

cooling ---

223

241

272

--- --- --- ---

T0-Onset of melt, Tm -Melting point, Tc - Completion of the melt


128

Figure 23 DSC thermograms of different Mefenamic acid crystals

SC- Super cooling crystals, CS-Commercial sample, RS- Recrystallized crystals, SA-

Spherical crystals, SD- Spray dried crystals, FD- Freeze dried crystals.


129

5.6.7 FT-IR Spectroscopy:

FTIR studies were performed in order to aid the evaluation of any possible

chemical interaction between the drug mefenamic acid and solvents during

crystallization184, 185

. Moreover, molecular level characterization of crystals can also

be obtained by performing FTIR studies. The FTIR spectrum for commercial sample,

spherical crystals, spray dried crystals, freeze dried crystals, recrystallized crystals

and super cooling crystals are shown in Figure 24 and Table 21.

The FTIR spectrum for mefenamic acid shows a weak peak at 3400 cm ⁻1 due

to the presence of a secondary amine. The broad band in the range of 3200-2900 cm

⁻1 is due to the presence of –OH [1, 2]. The same also represents the intra- and

intermolecular hydrogen bonding due to the –OH groups and also overlaps with the (–

CH3) group. The peak at 1650- 1750 cm⁻1 is due to the presence of a C=O group.

The presence of a peak at 1000 cm ⁻1 indicates the presence of a phenyl group186, 187

.

All the prepared Mefenamic acid crystals have exhibited general characteristic

peaks (Table 21). Specific changes in IR spectra are not very clear, could be due to

variations in the resonance structure, rotation of a part of a molecule or certain bonds.


130

Table 21 FT-IR data of Mefenamic acid crystals

Assignment

(Group)

Frequency

CS(in cm-1

)

Frequency

RS(in cm-1

)

Frequency

SA(in cm –1

)

Frequency

SD (in cm–1

)

Frequency

FD(in cm–1

)

Frequency

SC (in cm–1

)

secondary amine 3400 3400 3400 3400 3400 3350-3400

–OH

group

3200-2900 3200-2900 3200-2900 3200-2900 3200-2900 3100-2800

C=O

group

1650- 1750 1650- 1750 1650- 1750 1650- 1750 1650- 1750 1600- 1700

phenyl group 1000 1000 1000 1000 1000 1000

SC- Super cooling crystals, CS-Commercial sample, RS- Recrystallized crystals, SA- Spherical crystals, SD- Spray dried crystals, FD- Freeze

dried crystals.


131

Figure 24 FT-IR spectra of Mefenamic acid crystals SC- Super cooling crystals, CS-Commercial sample, RS- Recrystallized crystals, SA-



132

5.6.8 X-ray analysis:

The characteristic peak of the Mefenamic acid appeared in the 2θ range of 0–

600. All the prepared crystals of mefenamic acid showed similar peak positions (2θ) in

X-ray diffraction, formation of different polymorphs of Mefenamic acid was ruled

out, except super cooling crystals. However, the relative intensities of XRD peaks

were modified (Figure 25). This was attributed to the markedly different crystal habits

of the crystals173, 182

. Therefore the relative abundance of the planes exposed to the X-

ray source would have been altered, producing the variations in the relative intensities

of the peak or this may be due to differences in crystal size189

.

The commercial sample of mefenamic acid exhibits its characteristic

diffraction peaks at various diffraction angles indicating the presence of crystallinity.

The X-ray diffraction of the SC of drug showed the more peaks than other prepared

crystals and commercial sample this could be due to the degradation of drug by

heating or it could be variations in the resonance structure, rotation of a part of a

molecule or certain bonds. Alteration could be due to minor distortion of bond angles

and this lead to chances of conversion of mefenamic acid to another form in super

cooling crystals, the intensity of major peaks were lower than commercial sample due

to the differences in crystal sizes. The X-ray diffraction pattern of the all prepared

crystals showed that peak intensity was much lower than the commercial sample.

The crystalline peaks associated with prepared Mefenamic acid crystals were

of low intensity compare to commercial sample of Mefenamic acid. These findings

suggested that Mefenamic acid crystal habit were modified, to show improve

micromeritic properties by different techniques, these finding are in agreement with

previous study on Different NSAIDs drugs199

.


133

The Data obtained from X-ray powder diffraction studies are reported in

Tables 22, 23, 24, 25, 26 and 27. The cell parameters a, b, c, α, β, γ and the cell

volume for all the crystals of Mefenamic acid reported in Table 28.

Table 22: XRD data for commercial Mefenamic acid crystals

Peak

number

h k l 2 Ө

(Observed)

2 Ө

(Calculated)

Diffraction

1 0 0 1 .005766 .005762 .000005

2 1 0 2 .010459 .010544 -.000084

3 1 0 1 .012156 .012141 .000015

4 0 1 1 .015708 .015718 -.000009

5 1 -1 1 .019058 .019028 .000029

6 0 -1 2 .021315 .021240 .000075

7 0 2 0 .024176 .024140 .000036

8 1 1 0 .026675 .026523 .000153

9 1 2 1 .034568 .034576 -.000008

10 -1 -2 1 .056575 .056656 -.000081

11 -1 1 1 .064607 .064634 -.000027

12 1 -3 1 .069008 .069013 -.000004

13 1 -2 1 .076903 .065634 -.000017

14 1 2 4 .087887 .087880 .000007

Lattice Parameters

A 7.5631

B 9.0832

C 10.472

98.942

Β 92.521

57.965

Unit cell Volume 602.361

Space group Triclinic

h, k, l – Miller indices.

a, b, c – three sides of cell expressed in A0.

, β, - three angles of the cell expressed in degrees.


134

Table 23: XRD data for Mefenamic acid Recrystallized sample

Peak

number h k l

2 Ө

(Observed) 2 Ө (Calculated) Diffraction

1 0 -1 1 .005988

2 0 0 1 .006142 .006108 .000035

3 1 0 0 .008167 .008170 -.000003

4 1 0 1 .011292 .011272 .000020

5 1 1 0 .013231 .013248 -.000018

6 0 -1 2 .016464 .016476 -.000012

7 -1 1 0 .018395 .018524 -.000129

8 0 1 1 .021542 .021659 -.000117

9 1 1 1 .024176 .024185 -.000009

10 -1 -2 1 .027212 .027202 .000011

11 -1 1 1 .035563 .035473 .000090

12 -1 0 2 .038596 .038612 -.000016

13 -1 2 0 .044334 .044310 .000024

14 1 1 2 .047364 .047338 .000026

15 1 2 1 .027212 .052531 -.000009

16 0 2 1 .021542 .052643 -.000117

17 2 2 0 .052923 .052993 -.000070

18 -1 -3 2 .027212 .053132 -.000016

19 1 -3 2 .056939 .056936 .000003

20 -2 1 1 .035563 .065626 .000090

21 0 -2 4 .065857 .065905 -.000048

22 0 3 0 .047364 .069445 .000026

23 2 0 3 .047364 .069614 -.000009

24 1 3 0 .069807 .069702 .000105


135

Lattice Parameters

A 10.443

B 11.743

C 13.053

71.492

Β 99.071

112.02

Unit Cell Volume 1406.87






136

Table 24: XRD data for Mefenamic acid spherical agglomerates

Peak

number

h k l

2 Ө

(Observed)

2 Ө

(Calculated)

Diffraction

1 0 1 1 .005886 .005861 .000025

2 0 0 1 .006771 .006770 .000001

3 1 0 1 .016344 .006854 .000009

4 0 1 0 .007756 .007744 .000012

5 1 0 0 .010922 .010914 .000009

6 1 0 2 .016344 .016335 .000009

7 1 2 2 .018185 .018144 .000041

8 .021064 .010914 .000009

9 1 2 3 .000046 .023858 .000046

10 1 1 3 .023909 .023863 .000046

11 1 2 1 .025921 .025971 -.000049

12 2 2 2 .034663 .034673 -.000009

13 1 -1 2 .038596 .038663 -.000067

14 2 0 0 .043690 .043655 .000035

15 0 -1 2 .052222 .052132 .000090

16 -1 0 2 .059596 .059653 -.000058

17 2 -2 1 .066161 .066158 .000003

18 0 3 0 .069807 .069699 .000108

19 0 2 4 .059596 .070071 .000090


137

Lattice Parameters

A 10.437

B 12.995

C 12.346

85.368

β 91.947

115.84







138

Table 25: XRD data for Mefenamic acid spray dried crystals

Peak

number

h k l

2 Ө

(Observed)

2

Ө(Calculated)

iffraction

1 0 1 0 .003136 .003137 -.000001

2 1 2 0 .014726 .014729 -.000004

3 3 0 0 .019683 .019632 .000051

4 0 1 1 .030965 .031004 -.000039

5 .034695

6 3 3 0 .048033 .047865 .000168

7 1 4 0 .052222 .052374 -.000152

8 1 3 1 .058444 .058281 .000163

9 4 2 1 .075192 .075316 -.000124

Lattice Parameters

A 7.8356

B 10.582

C 17.068

107.256

β 39.080

96.540







139

Table 26: XRD data for Mefenamic acid Freeze dried crystals

Peak

number

h k l 2 Ө

(Observed)

2 Ө

(Calculated)

Diffraction

1 0 1 0 .003242 .003241 .000001

2 0 0 1 .014937 .015029 -.000092

3 3 1 0 .017355 .017420 -.000066

4 2 2 0 .019273 .019267 .000006

5 1 3 0 .030693 .030747 -.000054

6 2 2 1 .034377 .034296 .000080

7 .048033 .019267 .000006

8 0 4 0 .051873 .051861 .000012

9 5 1 1 .057669 .057657 .000012

10 1 2 2 .074778 .074657 .000121

11 6 1 1 -.000066 .074987 .019273

Lattice Parameters

A 10.774

B 11.696

C 10.204

93.462

β 109.49

117.20







140

Table 27: XRD data for Mefenamic acid Super cooling crystals

Peak number h k l 2 Ө Observed) 2 Ө (Calculated) Diffraction

1 1 1 0 .008597 .008551 .000046

2 0 0 1 .011127 .011115 .000012

3 0 2 0 .015514 .015481 .000033

4 -2 0 1 .019951 .019961 -.000010

5 1 1 1 .024661 .024604 .000057

6 0 1 0 .030965 .015481 .000033

7 1 2 1 .036147 .036215 -.000068

8 1 3 0 .039509 .039512 -.000003

9 -2 0 2 .043369 .043430 -.000061

10 -2 1 2 .047364 .047300 .000063

11 3 1 1 .030965 .071925 .000032

12 -3 2 2 .072273 .072438 -.000165

Lattice Parameters

A 8.7353

B 10.695

C 12.132

123.75

β 81.623

86.806







141

Table 28: Different cell parameters obtained for Mefenamic acid crystals From

XRD data

Different crystals of

Mefenamic acid

A B C α β γ Unit cell volume

Commercial sample 16.49 13.75 4.61 90 90 90 1046.691

Recrystallized

crystals

19.40 13.53 6.28 90 90 90 1649.86

Super cooling

crystals

11.98 12.38 7.77 90 110 90 1084.10

Spherical crystals 15.53 13.76 6.98 90 90 90 1156.16

Spray dried crystals 15.49 13.70 5.54 90 90 90 1177.77

Freeze dried crystals 15.50 14.01 9.21 90 90 90 2001.88


142

Figure 25: X-ray diffraction spectra of Mefenamic acid

SC- Super cooling crystals, CS-Commercial sample, RS- Recrystallized crystals, SA-



143

5.6.9 Surface topography by scanning electron microscopy (SEM):

Crystals of commercial sample are of the smallest size (5-10 µm) and they

have irregular shapes. Recrystallization leads to crystals with intermediate size (7-18

µm) which had rod or needle like shapes. The spherical agglomerates had a rough

surface covered with numerous rod shaped crystals (1221-1624 µm). The shape of

prepared spray dried crystals is uniform and was spherical in shape with small size (4-

12 µm). The freeze dried crystals had a smooth surface with very small in size

(average particle size 257 nm) (Figure 29) and in case of super cooling, crystals were

irregular shape, having rough surface with yellowish colour (21-37 µm).

The photomicrograph of Mefenamic acid commercial sample, recrystallized

sample, spherical crystals, spray dried crystals, freeze dried crystals and super cooling

crystals are shown in the Figures 26, 27 & 28.


144

Figure26: SEM of Mefenamic acid commercial and recrystallized crystals

Figure 27: SEM of Mefenamic acid Spherical and spray dried crystals


145

Figure 28 SEM of Mefenamic acid Freeze dried and super cooling crystals

Figure 29: Particle size distribution graph of Mefenamic acid Freeze dried

crystals by Malvern analyzer


146

5.7 Evaluation of prepared crystals:

5.7.1 Micromeritic properties:

The differences in the bulk densities may be related to their markedly different

crystal habits, leading to different contact points, frictional and cohesive forces

between the crystals. Spherical crystals, spray dried crystals, freeze dried crystals,

recrystallized and super cooling crystals exhibited higher packing ability than

commercial sample. It is due to lower surface area and wide particle size distribution.

The smaller crystals might have settled in voids between larger particles.

Three measures of flowability were utilized to analyze the flow properties (a)

flow rate (b) angle of repose and (c) compression index. Granules or powder must

adequately flow from holding container during pharmaceutical manufacture. Flow

rate measurement allows quick estimation of flow properties. It is the length of time

required for the flow of unit mass of substance through the orifice. Angle of repose is

able to provide gross measurements of the flowability of crystals. Most free flowing

materials have angle of repose less than 300. Powders with angles greater than 50

0

have flow problems. Commercial sample exhibited higher angle of repose than

prepared crystals that could be due to the irregular shape and small size of crystals,

which put hurdles in the uniform flow of crystals from funnel. The higher flowability

of the prepared crystals is due to perfect sphericity and particles size of the crystals.

Carr’s index & Hausner’s ratio were also used to assess the flow and compressibility

properties of the crystals. The compressibility index is a simple and fast method for

estimating flow of powder. Carr’s index showed the relationship between the

compressibility index and flowability. Different micromeritic properties of

Mefenamic acid commercial sample and prepared crystals are given in Table-29.


147

Angle of repose properties

less than 20 excellent flow

between 20-30 good flow

between 30-34 Pass flow

greater than 40 poor flow

The carr’s index, Hausner’s ratio of commercial sample is 36.13± 0.11% &

1.56 ± 0.21 respectively (n = 3), indicating extremely poor flow properties. Hausner

ratio was related to interparticle friction. Powders with Hausner’s ratio less than 1.25

indicates good flow (= 20% Carr) due to low inter-particle friction. Value greater than

1.5 indicates poor flow (= 33% Carr), such powder are more cohesive, less free-

flowing powders such as flakes. Flow rates are in agreement with morphology and

bulk density data that spherical crystals with low bulk density exhibits better flow

properties.

Relationship between powder flowability and % compressibility

Flow description % compressibility

Excellent flow 5 – 15

Good 16 – 18

Fair 19 – 21

Poor 22 – 35

Very poor 36 – 40

Extremely poor > 40


148

Table 29 Micromeritic and mechanical properties of Mefenamic acid commercial sample and prepared crystals

Properties Commercial

sample

Recrystallized

crystals

Spherical

crystals

Spray dried

crystals

Freeze dried

crystals

Super cooling

crystals

Particle size (m) 5-10 7-18 1221-1624 4-12 257 nm 21-37

Flow rate (gm/Sec) No flow No flow 8.37 4.53 3.93 9.18

Angle of repose (Ө)* 32.17± 1.28 30.96± 2.2 27.63± 1.46 26.23± 1.37 19.26 ± 2.21 25.84± 1.43

Tapped density

(gm/ml) * 0.487± 0.13 0.486± 0.11 0.419± 0.03 0.375± 0.19 0.365± 0.21 0.401± 0.18

Bulk density

(gm/ ml) * 0.311± 0.16 0.343± 0.11 0.395± 0.13 0.358± 0.14 0.367± 0.20 0.338± 0.2

Carr’s index (%)

(compressibility

index)*

36.13± 0.11 29.42± 0.02 5.72± 0.01 4.53± 0.2 1.89± 0.31 15.82± 0.12

Hausner’s Ratio* 1.56± 0.21 1.41± 0.20 1.06± 0.01 1.04± 0.11 1.01± 0.30 1.18± 0.14

Friability (%)* - - 0.654±0.12 - - -

Tensile strength*

(Kg/cm2) 6.56 ±0.11 8.18 ±0.04 5.24 ±0.02 7.39 ±0.03 8.41 ±0.01 10.53 ±0.03

*Standard deviation, n = 3.


149

5.7.2 Mechanical properties:

a. Tensile strength

Prepared crystals exhibited superior compressibility characteristics compared

to commercial sample except super cooling crystals (Figure 30 & Table-29). The FD

crystals showed maximum tensile strength and super cooling crystals shows minimum

tensile strength than the commercial samples of mefenamic acid. This could be due to

the fact that during the process of compression fresh surfaces are formed by

fracturing. Surface freshly formed by fracture enhanced the plastic inter particle

bonding, resulting in a lower compression force required for compressing the

prepared crystals under plastic deformation164, 168

.

Figure 30: Tensile strength of commercial crystals of mefenamic acid and

prepared crystals

b. Crushing strength

The crushing strength of the mefenamic acid spherical crystals was in the

range of 95 - 105 gm and was unaffected by the process variables164, 166, 168

.

0

2

4

6

8

10

12

0 1000 2000 3000 4000 5000 6000

Ten

sile

str

ength

Kg/c

m2

Compaction Pressure Kg/cm2

CS RS SC SA SD FD


150

Mefenamic acid: the effect of compression on compact strength is shown in Figure

30. Compact strength were in the order super cooling > freeze dried > recrystallized >

spray dried > commercial sample > spherical crystals. It can be intended that the

increases in compression force increased the compact hardness.

A high slope of a linear relation of compression force verses hardness suggests the

potential problems of capping. Since a small change in pressure could cause

significant change in compact strength.

A linear relationship between tensile strength and compression pressure was observed

for all crystallized sample of mefenamic acid.

c. Heckle analysis

Heckel plot is density-compression force relationship to determine the plastic

behavior of materials.

The slope of the Heckel plot (k) is indicative of the plastic behavior of the

material. A larger value for the slope is related to a greater amount of plasticity in the

material. This indicates that prepared crystals exhibited a higher degree of packing in

the die as a result of die filling than commercial sample. The differences between the

powders are not large, and this is expected because the materials are similar.

Considering slopes and their Standard mean Error, it is difficult to conclude whether

there are real differences between the plastic properties of different types of crystals.

A good rule of thumb is that, if Confidence intervals are not overlapping, then the

differences in plasticity are significant. When two confidence interval are greatly

overlapping, the plasticity of the materials is considered the same (193

). Generally, the

plasticity decreases in the following order: FD >SD >SA >SC >RS >commercial


151

sample of mefenamic acid. Constants of Heckel plot are given in Table 30 and Figure

31.

Table 30: Heckel parameters and elastic recovery of piroxicam prepared crystals

Parameters

Commercial

sample

Recrystallized

crystals

Spherical

crystals

Spray dried

crystals

Freeze dried

crystals

Super cooling

crystals

PY 64.4 ±0.21 66.01±0.31 67.21±0.13 67.54±0.37 68.2 ± 0.72 57.01±0.23

D0 0.554 ±0.07 0.484±0.02 0.467±0.01 0.458±0.13 0.442 ±0.03 0.513±0.25

DA 0.639 ±0.03 0.593±0.02 0.519±0.17 0.523±0.03 0.501 ±0.03 0.596±0.01

D’B 0.152 ±0.02 0.182±0.01 0.195±0.02 0.217±0.02 0.237 ±0.01 0.176±0.03

Elastic

recovery (%)

3.83 ± 0.12 4.37±013 4.89±0.11 5.19±003 5.30 ± 0.01 418.±013

Slope 0.00030 0.00035 0.0031 0.0038 0.0042 0.00072


152

Figure 31: Heckle profiles of different crystals of Mefenamic acid

The powder column formed by FD & SD was more densely packed than that

formed by CS in the initial stages of rearrangement as indicated by their Do values

(Table 22). The particles of FD & SD powder are larger, highly composed of

spherical- to oval-aggregates with few primary particles which are irregular compared

to those of CS. which are small and irregular primary particle. These features of the

latter could result to formation of bridges and arches, which could in turn prevent

close packing of the particles in the bulk state. Thus it seems that the values for the

relative density or the packing fraction in the bulk state are strongly dependent on the

particle size and shape.

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000 6000

In [

1/(

1.-

D)]

Applied pressure (kg)

CS RS SC SA SD FD


153

The low Da values for FD & SD are an indication that it opposes the

densification process less strongly than commercial crystal. Da describes the share of

densification due to contact area between particles; therefore, the low Da value of FD

is an indication of low contact area between the particles. However, it has been

reported that the resultant contact area in a powder bed is dependent upon the

interplay of several variables ranging from specific surface area (sequel to particle

size), particle size distribution, particle shape to surface properties of the powders

such as hardness of the surface.

Db, which describes the phase of rearrangement of particles, the extent of

which depends on the theoretical point of densification at which deformation begins,

was also determined for the cellulose powders; FD has a higher value than CS. FD

crystals were more resistant to movement once the initial phase of packing (as a result

of die filling) had been completed. This could be attributed to the high cohesive forces

likely present as a result of its amorphous nature, being an Freeze crystals.

The mean yield pressure, Py, values were calculated from the slope of the

linear line constructed over the compression pressure range (Table 22). Py which is

inversely related to the ability of the material to deform plastically under pressure was

found to be higher for FD. The results therefore indicate that FD underwent plastic

deformation more easily and rapidly than CS. This also confirms that FD is somewhat

resistant to deformation.


154

5.7.3 Solubility studies:

All the prepared crystals of mefenamic acid showed increased solubility than

the commercial sample in water and in pH 7.4 Phosphate buffer, The freeze dried

crystals showed highest solubility than commercial sample of mefenamic acid both in

water as well as in pH 7.4 phosphate buffer. The solubility of super cooling particle

showed least solubility than commercial sample both in water as well as in pH 7.4

phosphate buffer (Table 31)164, 166, 168

.

Increased solubility may be due to the increased wettability of the prepared

crystals or reduction in particle size & change surface properties of the prepared

crystals173, 200

.

In the case super cooling crystals, the poor solubility could be due to the

degradation of drug during heating or it could be due to variations in the resonance

structure, rotation of a part of a molecule or certain bonds. Alteration could be due to

minor distortion of bond angles171, 172, 173, 182

.

The solubility of prepared crystals of mefenamic acid in water and in pH 7.4

Phosphate buffer presented in Table 31;


155

Table 31: Solubility of different crystals of Mefenamic acid

Mefenamic acid Samples In Water(mg/ml)

(±SD)

In pH 7.4(mg/ml)

( ±SD)

Commercial sample 0.0083±0.01 0.0737±0.01

Recrystallized crystal 0.0094±0.02 0.0778±0.02

Super cooling crystals 0.0037±0.02 0.0239±0.01

Spherical crystals 0.0437±0.02 0.1602±0.01

Spray dried crystals 0.0526±0.01 3.7645±0.02

Freeze dried crystals 0.1237±0.02 4.6520±0.02

*Mean SD± n=3


156

5.7.4 Dissolution behaviour of crystals:

Dissolution studies were conducted using USP dissolution apparatus XXIV-

Type II as per the monograph for mefenamic acid tablets. But in this study crystals

were directly added to the dissolution medium. Encapsulating the drug was avoided,

as dissolution of shell will add one more parameter to the result. Amount of

mefenamic acid dissolved – time data are reported in the Table 32 for commercial

sample and for prepared crystals, Dissolution profile of the mefenamic acid

commercial sample, recrystallized sample and spherical crystals is shown in the

Figure 32.

Percentage drug dissolved in 10 min is rapid in all the samples. The

commercial sample showed a plateau region in its dissolution profile. This could be

attributed to the super saturation of unstable form of drug with its stable form. Drug in

contact with solvent mixtures the transformation of rate depends on the mobility of

the molecule in the solid, the type of structural change that take place and

environment factor. The larger the difference between the packaging arrangements of

two forms the slower the rate of conversion from unstable form to stable form.

The dissolution profiles of mefenamic acid exhibited improved dissolution

behaviour for prepared crystals than commercial sample, except super cooling

crystals. The reason for this faster dissolution could be linked to the better wettability

of the prepared crystals or reduction in particle size of the prepared crystals. The

amount of drug dissolved in 60 min greatly varied for all prepared crystals164-168

.

Difference in the dissolution and solubility profile of the modified Mefenamic

acid may also be due to the difference in crystal structure. Solvents with varying

polarities and desolvation process affect crystal formation, leading to different


157

morphologies and properties of crystals obtained from different solvent mixtures and

present research work result are accordance with the previous research finding result

201.

Dissolution of super cooling crystals of mefenamic acid was not improved

than commercial sample; these findings are in agreement with the previous findings

171, 173.

Further, the results of dissolution studies were submitted to two analysis of

variance using graph pad instat programme in order to determine significant

differences. ANOVA results showed that the critical value of F at 5% level of

significance (4.366%) with p value 0.0038, between the treatments. Freeze dried

crystals has more significant influence on the dissolution of than others prepared

crystals. (26.71), and super cooling crystals shown no significant influence on the

dissolution (0.06). Paired t – test was applied so that comparisons of two means are

made on related samples. Pairing was found to be effective for all the crystals

dissolution profiles except super cooling crystals. Significant differences were

observed for dissolution rate of all the prepared crystals except super cooling crystals

(p>0.05), in the following order FD (0.004)>SD (0.0002) >SA (0.00002)>RS

(0.003)>SC (0.12).


158

Table 32: Dissolution data of Mefenamic acid crystals in Phosphate buffer pH7.4

Sl. No Time

(in min)

CS

% release

mean ±S.D.*

RS

% release

mean ±S.D.*

SA

% release

mean ± S.D*

SD

% Release

mean ± S.D*

FD

% release

mean ± S.D*

SC

% release

mean ± S.D*

1 0.00 0.00±0.34 0.00 0.00 0.00 0.00 0.00

2 10 1.17±0.04 2.13±0.04 17.13±0.30 15.71±0.01 7.91±0.05 0.090±1.01

3 20 4.06±0.01 5.56±0.01 20.41±0.02 19.52±0.02 18.04±0.01 0.091±2.02

4 30 5.09±0.02 7.78±0.20 22.91±0.02 25.36±0.03 25.32±0.02 --

5 40 9.47±0.05 11.92±0.02 26.76±0.12 29.97±0.03 35.62±0.01 --

6 50 13.9±0.01 14.61±0.04 30.65±0.23 36.55±0.04 43.77±0.34 --

7 60 18.5±0.11 20.40±0.01 35.73±0.25 48.13±0.02 56.31±0.04 --

*Standard deviation, n = 3.

Figure 32: Dissolution profile of different Mefenamic acid Crystals in Phosphate

buffer pH7.4

CS-Commercial sample, RS- Recrystallized sample, SC- Super cooling, SA-

Spherical crystallization, SD- Spray dried, FD- Freeze dried.

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

% R

elea

se

Time (min.)

Pure M.acid RS SC SA SD FD


159

5.7.5 Various parameters of model fittings of Mefenamic acid samples

Table 33: Data of various parameters of model fittings of Mefenamic acid

samples

Drug Different

crystals

Zero

Order

(r2)

First

Order

(r2)

Higuchi

(r2)

Korsemeyer

/ Peppas

(r2)

n Value

Peppas

Mefanamic

acid

CS 0.9522 0.3388 0.7744 0.7791 0.5671

SA 0.8804 0.3248 0.9837 0.9380 0.6723

RS 0.9795 0.3407 0.8408 0.9184 0.5972

FD 0.9961 0.2343 0.8904 0.9975 0.7842

SD 0.9612 0.2842 0.9402 0.9704 0.8734

SC - - - - -

The release kinetics was evaluated by using zero order, first order, Higuchi’s

diffusion and Korsemeyer - Peppas equation. Calculated regression co efficient values

for different crystals are tabulated in Table 33. These values are compared with each

other for model equation. Based on the higher regression values (r2), the best fit model

was zero order for all the prepared crystals and the drug release kinetics followed

diffusion controlled mechanism. Release kinetic profile of Mefenamic acid crystals

for zero order, first order, Peppas and Higuchi are presented in Figure 33. The Peppas

model is widely used, when the release mechanism is not well known or when more

than one type of release phenomenon could be involved. ‘n’ value could be used to

characterize different release mechanism.

‘ n’ Mechanism of drug release

0.5 Fickian diffusion

0.5 < n < 1 Non fickian diffusion

1 Case II transport

The ‘n’ values obtained graphically from peppas plot are shown in Table 25. As the

values obtained were more than 0.5, indicates that the release approximates non

fickian diffusion for all the prepared crystals of mefenamic acid.


160

Figure 33: Release mechanism of Mefenamic acid


161

5.7.6 Stability study:

The dissolution behaviour of Mefenamic acid prepared crystals shall remain unchanged during storage. The results of the

stability study (Table 34) of prepared crystals of Mefenamic acid stored at 400C and 75% relative humidity for 6 month with

accordance with ICH guidelines194

. The influence of physical stability on the prepared crystals was investigated. The results of

stability presented in the Table 34.

Table 34: Stability data of prepared crystals of mefenamic acid by different crystallization techniques

Sample name: Mefenamic acid Spherical crystals

Storage condition: 400C /75% RH

Testing interval Description of drug FT-IR Study XRD Study Drug content ( ±SD) Dissolution Study (±SD) Water content (%w/w)

Initial Light yellow crystals Complies Complies 98.46±0.01 35.73±0.03 4.34

1 month Complies Complies Complies 98.36±0.01 35.71±0.02 --



6 month Complies Complies Complies 97.53±0.02 35.54±0.02 4.39

Sample name: Mefenamic acid Spray dried crystals







Sample name: Mefenamic acid Freeze dried crystals







Prepared crystals of mefenamic acid were stable and compiled with its all the properties when compare to freshly prepared

crystals of Mefenamic acid.


162

5.8 Preparation of conventional tablet:

Mefenamic acid conventional tablets were prepared by direct compression using direct

compressible excipients.

5.8.1 Evaluation of Mefenamic acid tablets:

Tablets containing pure sample and prepared crystals were evaluated for Average

weight, hardness and percentage friability the limit (Table 35). Percentage weight

variations, content of active ingredient were within IP limits.

Table 35: Evaluation of prepared Mefenamic acid tablets

Different

crystals Formulations

Average

weight

(mg) ( ±SD)

Hardness in

kg/cm2

(±SD)

Friability*

(%) ( ±SD)

Content

uniformity*

(%) ( ±SD)

Commercial

sample

CS1 251.7±2.9 5.12±0.96 0.56±0.71 101.31±0.23

CS2 253.3±2.8 5.02±0.13 0.41±0.92 99.18±0.21

Spherical

crystals

SA1 250.7±1.8 5.23±0.41 0.63±0.51 99.66±0.13

SA2 251.5±3.0 5.51±0.43 0.34±0.11 99.33±0.11

Spray dried

crystals

SD1 251.3±2.4 5.17±0.25 0.72±0.65 99.86±0.03

SD2 249.7±2.9 5.52±0.76 0.44±0.11 99.51±0.83

Freeze

dried

crystals

FD1 251.6±2.8 5.22±0.63 0.21±0.32 99.88±0.41

FD2 248.7±1.8 5.30±0.51 0.34±0.21 99.36±0.57

Super

cooling

crystals

SC1 252.05±1.0 5.16±0.48 0.89±0.47 24.63±0.13

SC2 250.23±1.9 5.51±0.26 0.73±0.66 23.96±0.03

Marketed

product MP 250.93±0.9 5.42±0.79 0.26±0.21 99.81±0.43

1-Sodium starch glycolate,

2-Povidone, MP-=Market Product

*Mean SD± n=3

5.8.2 Dissolution studies of tablets:

Dissolution studies of prepared tablets were performed using USP XXIV

dissolution test apparatus Type II. The dissolution profile is shown in the Figure 34 & 35.

The dissolution profiles of Mefenamic acid tablets contains spherical crystals, spray dried

and freeze dried crystals exhibited better dissolution behavior than tablets contains


163

commercial sample. In case of crystals prepared by Recrystallization and super cooling

techniques dissolution is not enhanced as compare to other techniques. Percentage release

of mefenamic acid from super cooling crystals was very low when compare to commercial

sample, this may be due to the change in crystals habit or change in the crystal morphology

due to heat But the dissolution profile of the marketed tablets is much better than the tablets

prepared by different crystallization techniques. Table 36 & 37 contain the release data of

Mefenamic acid from prepared Mefenamic acid tablets (1-

Sodium starch glycolate, 2-

Povidone) and marketed tablets respectively.

Further, the results of dissolution were submitted to two analysis of variance using

graph pad instat program in order to determine significant differences. ANOVA results

showed that the critical value of F at 5% level of significance (4.03), between the

treatments. Tablets containing Freeze dried crystals has more significant influence on the

dissolution of than others Tablets contains crystals. (47.39) and super cooling crystals had

shown not significant influence on the dissolution (1.67).

Paired t – test was applied so that comparisons of two means are made on related

samples. Pairing was found to be effective for all the crystals dissolution profiles except

super cooling crystals. Significant differences were observed for dissolution rate of all the

prepared crystals i.e. (p>0.05), except super cooling crystals, in the following order FD

>SD >SA >RS >SC.

Table 36: Dissolution data of prepared Mefenamic acid and market tablet in

Phosphate buffer pH7.4

Sl.

No.

Time

(in

min)

CS1

Average

% release

mean±SD*

RS1

Average

% release

mean±SD*

SA1

Average %

release

mean±SD*

SD1

Average

% release

mean±SD*

FD1 Average

% release

mean±SD*

SC1 Average

% release

mean±SD*

MP Average

% release

mean±SD*

1 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00

2 10 17.1±0.03 15.72±0.11 18.0±0.33 19.3±0.05 20.2±0.03 0.36±0.03 21.21±0.02

3 20 20.4±0.01 19.63±0.11 25.2±0.22 29.4±0.06 29.4±0.02 0.94±0.02 32.52±0.04

4 30 23.1±0.13 25.35±0.13 35.5±0.01 47.8±0.03 47.8±0.04 1.54±0.06 48.76±0.05

5 40 27.1±0.11 29.91±0.03 43.6±0.02 60.9±0.04 64.9±0.01 2.15±0.07 68.10±0.01

6 50 31.6±0.12 36.52±0.13 56.2±0.04 69.2±0.04 79.5±0.05 2.82±0.02 83.20±0.04

7 60 36.0±0.12 45.01±0.15 67.2±0.17 79.8±0.03 89.9±0.06 3.91±0.01 95.21±0.05

1-Sodium starch glycolate


164

Figure 34: Dissolution profile of Mefenamic acid from prepared tablets in Phosphate

buffer pH7.4

CS-Commercial sample, RS- Recrystallized sample, SC- Super cooling, SA- Spherical

crystallization, SD- Spray dried, FD- Freeze dried, MP-Market product.

Table 37: Dissolution data of prepared Mefenamic acid and market tablet in

Phosphate buffer pH7.4

Sl.

No.

Time

(in min)

CS2

Average %

release

mean±SD*

RS2

Average %

release

mean±SD*

SA2

Average %

release

mean±SD*

SD2

Average %

release

mean±SD*

FD2

Average %

release

mean±SD*

SC2

Average %

release

mean±SD*

MP

Average %

release

mean±SD*

1 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00

2 10 14.11 14.22 18.53 18.40 19.53 0.35 21.21

3 20 18.20 18.43 25.52 27.86 27.54 0.98 32.52

4 30 21.43 23.53 33.64 45.85 44.63 1.46 48.76

5 40 25.42 27.43 41.53 61.32 63.53 2.13 68.10

6 50 29.89 33.64 55.63 68.43 78.53 2.91 83.20

7 60 34.42 43.65 65.78 77.63 86.32 3.92 95.21

2-Povidone

-20

0

20

40

60

80

100

120

0 10 20 30 40 50 60

% R

ele

ase

Time (min)

CS RS SC SA SD FD MP


165

Figure 35: Dissolution profile of Mefenamic acid from prepared tablets in Phosphate

buffer pH7.4


crystallization, SD- Spray dried, FD- Freeze dried, MP-Market product.

Dissolution data analysis:

Differential and Similarity factor for prepared tablets formulations

Formulations

Differential

Factor

(f 1)1

Differential

Factor

(f 1)2

Similarity

Factor

(f 2)1

Similarity

Factor

(f 2)2

CS 62.22 63.88 66.00 65.72

RS 52.75 54.18 69.40 67.53

SA 29.43 30.92 74.13 73.61

SD 16.19 18.47 80.63 79.18

FD 5.58 9.34 92.21 86.60

SC 95.94 95.93 61.26 61.30


crystallization, SD- Spray dried, FD- Freeze dried.

Differential factor (f1) and Similarity factor (f2) was calculated for prepared tablets

containing crystals (1 & 2 formulation). The Differential factor (f1) for FD was nearer to 0

and for SC it shows >95. The Similarity factor (f2) for SA, SD and FD was more than 100

and for SC it was ~60 for both 1 & 2 formulations respectively.

From the above result it can be conclude that tablets containing FD crystals were

similar to marketed product and tablet containing SC crystals least similar222

.

0

20

40

60

80

100

120

0 10 20 30 40 50 60

% R

elea

se

Time (min)

CS

RS

SC

SA

SD

FD

MP

result and discussion - information and library...

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