microsoft word - lab 8

8/8/2019 Microsoft Word - Lab 8

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Pharos University

Faculty of Pharmacy & Drug Manufacturing

Principles and kinetics of Drug Stability Practical-PHR 416

Lab-8

Incompatibilities in Pharmaceutical PreparationsThe term incompatibility may be applied to pharmaceuticals when a problem arises during

the pharmaceutical compounding of more substances because of their therapeutic,, physical

or chemical properties, the substances are said to be incompatible. A preparation is

considered to posses an incompatibility when combination of its ingredients adversely affects

its appearance, elegance or therapeutic efficacy.

Incompatibility may be classified into three main groups: therapeutic, physical and chemical.

1. Incompatibility involving Surface active agentsTypes of surfactants:a-Anionic (-)

Ex: SLS, sodium stearate, potassium stearate.

b-Cationic (+)

Ex: cetrimide.

c- Amphoteric (+&-)

Ex: Betaines.

d-Non ionic

Ex: span & tween.

a.Interaction between oppositely charged surfactantsThe interaction occurs upon mixing anionic surfactants with cationic surfactants. This may be

manifested, visually, as turbidity or formation of a precipitate. The surface activity of both

materials will be drastically reduced.

This occurs upon mixing sodium lauryl sulphate with cetrimide.

Procedure:

1-add 2 ml of 0.1% w/v sodium lauryl sulphate.

2-add cetrimide solution (0.1%) drop wise, and observe any change in the clarity of the

solution.

3-add excess of cetrimide solution (about 5 ml )to the turbid solution and record any change.

b. Interaction between surfactants and drugs. Drugs may interact with surfactants carrying opposite charge.

The results of this type of interaction are:

I- reduction of the therapeutic effectiveness of the drug

II- reduction of the surface active property of the surfactant


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SAA and acidic drug or excipient :It occurs with soap surfactants which are salts of weak fatty acids easily displaced by

stronger acids.

e.g. Na Stearate + Salicylic acid stearic acid (ppt) + sodium salicylate

It results in loss of surface activity.

- SAA and Heavy metalse.g. Na Stearate + Ca+2 Ca Stearate (insoluble in H2O)

It can occur by hard water which contains divalent ions.

Practical experiments

Interaction in soap emulsions

Emulsions made with monovalent soap may undergo craking or phase inversion, if the

medium contains polyvalent ions or if the medium is acidic.

2 C17 H35 C OO Na +MgCl2 (C17 H35 C OO)2 Mg+2 NaCl

C17 H35 C OO Na + H+ C17 H35 C OO H + Na+

Turpentine liniment:R/

Soft soap 1.5 gm

Camphor 1 g

Turpentine oil 13 ml

Distilled Water 4.5 ml

Prepare 20 ml of turpentine liniment.

Procedure:

1. Dissolve the soft soap in water in a casserole by soaking soft soap in specified amountof water for 10 min on a water bath.

2. Dissolve camphor in turpentine oil.3. Add oil phase to soap solution with constant stirring in one and the same direction.4. Take 10 ml liniment in test tube & add 2 ml of 5 % CaCl2 solution, shake and observe

the stability of the emulsion cracking

5. Add 3ml of dilute hydrochloric acid to 10 ml of liniment shake and observe thestability of the emulsion cracking

Comment on your observation.

What will happen if amount of CaCl2 solution added is increase


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Sodium salicylate 3 gm

Lemon syrup 30 ml

Water to 100 gm

Send 25 ml

Procedure:1. Dissolve Na salicylate (or benzoate) in 15 ml water in a beaker.

2. Add lemon syrup and transfer to cylinder.

3. Complete volume to 25 ml and transfer to bottle.

4. Observe the clarity of this product.

5. Comment on your observation.

Repeat the above preparation, but using 30 % V/V of Lemon tincture in simplesyrup (10% V/V).

Compare the clarity of this preparation with previous one.3. Incompatibility of phenolic drugs with ferric ions

Phenolic drugs as salicylates, resorcinol, adrenaline and oxyphenbutazone, react with ferric

ions to give a violet green colour.

Source of ferric ions

1. As impurities in other chemicals or ingredients used in the formulation.2. From metallic containers e.g. tanks, mixers, spautals.3. Water if not distilled, may contain heavy metal impurities as ferric.The discolouration may occur immediately or after storage of the formula.

Treatment1. It is better corrected by avoiding the source of this interaction.2. It is prevented by the addition of ions such as tartrate or citrate which complex with ferric

ions.

A)prepare 25 ml of sodium salicylate mixture B.P.C. 25 %R/

Sodium salicylate 50 gm

Chloroform water (double strength) 500 ml

Water to 1000 ml

B) Repeat the above prescription by using water containing 100 ppm of iron and observe thecolour of the mixture.

C) Repeat the mixture B but using water containing 100 ppm of iron and 2 % Sodium citrate.

microsoft word - lab 8

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