EUROPEAN JOURNAL OF DRUG METABOLISM AND PHARMACOKINETICS, 1984, No 3, pp. 267-274

Pharmacokinetics of oxiracetam followingintravenous and oral administration in healthy volunteers

E. PERUCCA *, A. ALBRIC I **, G. GATTI *, R. SPALLUTO **, M. VISCONTI ** and A. CREMA ** Institute ofMedical Pharmacology. University ofPavia. Pavia.** ISF Laboratories for Biomedical Research. Trezzano SIN. Milan. Italy

Received for publication: January 30, 1984

Key-words: Pharmacokinetics, oxiracetam, bioavailability

SUMMARY

The kinetics of oxiracetam after single intravenous and oral doses (2000 mg) were investigated in four healthy volunteers. Follow­ing intravenous administration, the decline in serum levels showed a prolonged, rapid phase followed br a delayed terminal phase.Mean residence times ranged from 3.9 to 6.5 h. Volumes of distribution ranged from 0.9 to 1.81· kg- , whereas clearance valuesranged from 100to 119 ml·h -! kg- I More than 90% of the intravenous dose was recovered unchanged in the urine within 48 h. Oraladministration resulted in peak levels within 1-2h; thereafter, the decline in serum levels showed a pattern similar to that observedafter the intravenous dose - almost 50% of the oral dose was excreted in the urine within 6 h. The absolute availability of oral oxi­racetam was 75±7%.

INTRODUCTION

Oxiracetam (lSF 2522) (Figure I) is a recentlydeveloped psychotropic agent. This compound,which is classified as a nootropic agent, has been

HO

Fig. J. Structure of oxiracetam (4-hydroxy-2-oxo-l-pyrrolidinacetamide) (ISF 2522).

Send reprint requests to: Dr. A. Albrici, ISF Laboratoriesfor Biomedical Research, Trezzano SIN, Milan, Italy.

shown to improve learning and memory in normalanimals as well as in animals with acute andchronic cerebral impairment (1,2). The drug hasbeen reported to stimulate the turnover of phos­pholipids in the brain (3). In addition, oxiracetamhas recently been shown to reduce the cognitiveimpairment secondary to inhibition of acetylcho­line synthesis or blockade of muscarinic receptors,an effect which is probably mediated by increasedacetylcholine utilization (4).

In normal volunteers, single oral doses of oxi­racetam (200-2400 mg) have been described tocause a significant increase in the a. activity of theEEG (5). In a controlled study, Itil et at. (6) foundoxiracetam (400-2400 mg daily for 12 weeks) to besuperior to piracetam in improving memory func­tion in patients with organic brain syndrome. Tol­erability has been excellent in all studies.

So far, the kinetics of oxiracetam in man havenot been characterized, due to the lack of an ade­quate assay. We have now developed a highly spe­cific high performance liquid chromatographytechnique that allows the detection of concentra­tion as low as 0.5 ug/ml in human serum and urine.In the study described here, this method was usedto investigate the serum level profile and urinaryexcretion of oxiracetam after single oral and intra­venous administration in healthy volunteers.

268 European Journal of Drug Metabolism and Pharmacokinetics. 1984. No 3

METHODS

Subjects and protocol

Four healthy male volunteers aged between 20and 26 years (weight 71-84 kg) gave their writteninformed consent to take part in the study. Eachsubject received, in random order and at an inter­val of at least 2 weeks, one oral and one intrave­nous dose of oxiracetam (2000 mg). The oral for­mulation consisted of 5 x 400 mg capsules, whereasfor the parenteral study a 10-ml aqueous solution(200 mg/ml) was injected slowly into an antecubitalvein over 5 min. On both occasions the drug wasgiven after an overnight fast; no food was allowedduring the following 4 h. Blood samples were col­lected at 0,0.5, 1,2,4, 7.5, 10 and 24 h. Fractionalurine collections were obtained from each subjectover the following intervals: 0 (pre-drug), 0-2, 2-4,4-6, 6-12, 12-24 and 24-48 h after oral administra­tion and 0, 0-24 and 24-48 h after intravenousadministration. Urine and serum were kept frozenat - 20°C until analyzed.

Analytical method for oxiracetam in bio­logical fluids

Aliquots of urine (0.1 ml) or serum (0.5 ml) wereextracted twice with I ml of toluene, lyophilized,mixed with triphenylchlorosilane (300 mg) and pir­idine (I ml), and incubated at 60°C for 5 h. Themixture was neutralized with a saturated aqueoussolution of citric acid (8 ml), extracted with methy­lene chloride (10 ml), and evaporated to drynessunder a stream of nitrogen. The residue was recon­stituted with methylene chloride (2 ml), purified onSep-Pak cartridges by washing with a solution(10 ml) of methylene chloride: acetonitrile (9 :1),and eluted with 7 ml of acetonitrile: methanol(I :1). Then, 0.1 ml of a solution of the O-benzoylester of oxiracetam (internal standard) in acetoni­trile (50 ug/ml for urine and 5 ug/ml for serum) wasadded to the eluate, which was then dried undervacuum at 50°C and reconstituted with 0.5 ml ofacetonitrile. Fifty III of the final solution wasinjected into a Hewlett-Packard HP 1080 B highperformance liquid chromatograph connected to aVV detector (Perkin Elmer LC 55) set at 230 nm.The chromatographic separation was carried outunder isocratic conditions using a silica column(5 urn, Brownlee Laboratories) and a mixture ofhexane: isopropranol: water in the ratio of77 : 22.5 : 0.5 as eluent. The retention times were 6min for oxiracetam and 14 min for the internalstandard. The limits of quantitation of the methodwere 0.5 ug/ml and below 50 ug/ml for serum and

urine, respectively. All samples were analyzed induplicate (serum) or triplicate (urine). The preci­sion and accuracy were better than 4% and 3%,respectively.

Pharmacokinetic analysis

Following intravenous administration, the dis­appaearance of oxiracetam from serum was char­acterized by a rapid phase followed after 7.5 to 10 hby a slower phase. The kinetic profile could bedescribed by fitting the data to a two-compartmentopen model, assuming that the decrease in serumconcentration after 7.5 h (subject 2) or 10 h (sub­jects I, 3 and 4) reflected the terminal phase (B),Any possible error in the characterization of theterminal phase is unlikely to affect to an importantextent the estimate of the degree of excretion, sincethe urinary recovery of the drug at 24 h was already90% (see Discussion). Individual kinetic parame­ters were calculated as previously described (7,8).The steady-state volume of distribution (Vdss) withrespect to the two-compartment model was calcu­lated as Vdss = (I + KI2/K21)Vt (9,10).

In view of the limitation of compartmental anal­ysis (see Discussion), intravenous data were alsoanalyzed by model-independent calculations. Theareas under the curve (AVC) and the areas underthe first moment of the curve (AVMC) were deter­mined by the trapezoidal rule. Extrapolation toinfinity was achieved by conventional methods (9),assuming that the last concentration values ref­lected the terminal phase 0"2), The latter was esti­mated on the same points used to calculate ~. Forthe AVC, the extrapolated part comprised only4± 1%of the total area. For the AUMC, the extrap­olated area represented a greater fraction (28 ± 6%).The mean residence time (MRT), total body clear­ance (CI), renal clearance (Clren), volume of dis­tribution (Vdarea) and volume of distribution atsteady state (Vdss) were calculated according to thefollowing equations (7,9,11,12): MRT = AUMC/AUC; CI = dose/Al.Jf"; Clren = amount excretedin urine from 0 to 24 h/AVC from 0 to 24 h ;Vdarea = dose/(AUc-A2); Vdss = dose'AUMC/(AUC)2. The oral availability was estimated fromthe ratio between AVCs after oral and intravenousadministration.

RESULTS

Serum level data

The time course of serum oxiracetam concentra­tions following oral and intravenous administra­tion in each of the four subjects is illustrated in

E. Perucca et al.. Pharmacokinetics of oxiracetam i.v. and oral in volunteers 269

Figure 2. Mean values (± SEM) after intravenousand oral administration are also plotted on a semil­ogarithmic scale in Figure 3. The decline in serumoxiracetam showed a rapid phase followed after a

few hours by a slower phase. Since the data couldbe fitted satisfactorily by a bi-exponential equa­tion, pharmacokinetic parameters after intravenousdoses were calculated according to a two-compart-

cone. (pg/ml) co c.~g/ml)

-i.v.---os

24 time(hl

Subi·2

4 7.5 10

80--Lv.---os

24 time(hl

Subi.1

oJ,............:;:====I4---0.51 2 4 7.5 10

20

40

cone.(pg/ml)

80-i.v.---os

cone. (pg/ml)

80--Lv.---os

60 SUbi·3 60 Subi.4

40 40

20

-...;; -----4 7.510 24 time (h)

Fig, 2. Serum oxiracetam concentrations after intravenous and oral administration of a single dose (2000 mg) in four normal subjects.

270 European Journal of Drug Metabolism and Pharmacokinetics. 1984. No 3

ment model, assuming that the decrement in serumlevels after 7.5 to 10 h reflected the terminal phase.As illustrated in Table I, the half-life of the rapidslope approximated I h, whereas the terminal half­line, calculated over a period when the serum con-

300

centration had already decreased to very lowvalues, ranged from 6.1 to 10.8 h. The apparentvolume of distribution at steady state (Vdss) wasabout 0.5 l-kg - I. Results of non-compartmentalanalysis are reported in Table II. Mean residence

____ serum concentration (JJg/ml) i.v. dose

_____ serum concentration (,..g/ml) oral dose

_._ urinary excretion rate (mg/h ) oral dose

100

10

1

~\

''t,\'\

'1--"<,<,

<,

'l-·--.__.--.--.--.--. i--'--

0.1

, " 1~ i4time (h)

Fig. 3. Time course of serum oxiracetam concentrations after single oral and intravenous doses (2000 mg) and urinary excretion ratesafter a single oral dose. Symbols represent the mean ± SEM in four normal subjects.

E. Perucca et al.. Pharmacokinetics of oxiracetam i.v. and oral in volunteers 271

times ranged from 3.9 to 6.5 h. Total body clear­ance values averaged 109±5 ml·h-I·kg- I andshowed remarkably little interindividual variabil­ity. There was a good agreement between Vdssvalues calculated according to compartmental andnon-compartmental analysis (0.62 ± 0.08 vs.0.55 ± 0.08 l-kg'", respectively). As expected, valuesof Vdarea were consistently greater than values ofVdss'

As shown in Figure 2, oxiracetam was readilyabsorbed from the gastrointestinal tract. Peakserum levels were attained within 1-2 h after oralintake (Table III) ; thereafter, the decrease in serumlevels showed a biphasic pattern similar to thatseen after the intravenous dose. In view of thelimited number of sampling times, no attempt wasmade to characterize the rapid phase. The half-lives

of the delayed phase were similar to those calcu­lated after intravenous dosing. Bioavailabilityvalues, calculated from AUe ratios after oral andintavenous administration, respectively, rangedfrom 59 to 92% (Table 111).

Urinary data

Urinary excretion values are reported in Table IV.After intravenous administration, 88% and 93% ofthe dose could be recovered unchanged in urinewithin 24 and 48 h, respectively. The correspondingvalues after oral administration were 61% and 68%,respectively. Recovery was already substantial(47% of the dose) at only 6 h after oral intake(Figure 4). As shown in Figure 3, the decline in uri-

Table I: Pharmacokinetic parameters calculated from serum oxiracetam concentrations after single intravenous doses. Two-compart­ment open model.

A and B, extrapolated zero-time intercepts of the a and Il slopes, respectively; a and Il, rate constants of the a (rapid) and ~

(terminal) slopes, respectively; Ha and HIl, half-lives of the a and ~ slopes, respectively; KI2 and K21, transfer rate constantsrespectively from the central to the peripheral compartment and viceversa; Ke" elimination rate constant from the centralcompartment (VI); Vdss' volume of distribution at steady state.

Subject A a t l4a B {3 t l / 2 (3 K12 K21 Kel VI Vdss

(Ilg/ml) (h- I) (h) (Ilg/ml) (h- I) (h) (h- I) (h-I) (h- I) (Lkg-J) (I.kg-I)

1 120 0.743 0.9 11.1 0.113 6.1 0.184 0.166 0.506 0.21 0.44

2 101 0.847 0.8 11.1 0.111 6.2 0.233 0.169 0.556 0.20 0.47

3 62 0.559 1.2 8.7 0.100 6.9 0.145 0.156 0.358 0.31 0.60

4 77 0.690 1.0 4.7 0.064 10.8 0.212 0.100 0.442 0.31 0.97

Mean 90 0.710 1.0 8.9 0.097 7.5 0.193 0.148 0.465 0.26 0.62

±SEM ±13 ±Q.060 ±Q.l ±1.5 :lO.OII ±1.1 ±Q.019 ±Q.016 ±Q.043 ±Q.03 ±0.08

Table II: Pharmacokinetic parameters calculated from serum oxiracetam concentrations after single intravenous doses. Model inde-pendent analysis (see Methods for an explanation of abbreviations)

Subject AUC AUMC MRT Vdss Vdarea Cl Clren(J.Lg.ml-1.h) (J.Lg.ml- 1.h 2) (h) (I.kg- 1) (I.kg- 1) (ml.h-1.kg-1) (ml.h-1.kg-1)

1 281 1103 3.9 0.39 0.89 100 86

2 233 1025 4.4 0.45 0.92 102 96

3 207 1045 5.0 0.60 1.19 119 117

4 217 1400 6.5 0.75 1.80 115 103

Mean 235 1143 4.9 0.55 1.2 109 101

± SEM ±16 ± 87 ±0.06 ±0.08 ±0.2 ± 5 ± 7

272 European Journal of Drug Metabolism and Pharmacokinetics. 1984. No 3

Table JJI. Pharmacokinetic parameters calculated from serum oxiracetam concentrations after single oral doses and bioavailabilitydata

Subject Peak concentration Time of peak e/2~ AVC Bioavailability

(fJ.g. m1- 1) (h) (h) (fJ.g. m1-1.h) (%)

1 58 1 11.7 212 75

2 43 1 5.6 172 74

3 22 2 5.7 123 594 36 1 11.0 199 92

Mean 40 1.25 8.5 177 75

± SEM ±7 ±0.25 ±1.7 ±20 ±7

Table IV. Urinary excretion of unchanged oxiracetam at different intervals after oral and intravenous administration of a 2000 mgdose

Subject % Dose (oral administration) % Dose (iv administration)

0-2h 2-4 h 4-6h 6-12 h 12-24 h 24-48 h 0-48h 0-24 h 24-48 h 0-48h

1 26.0 15.6 8.4 10.7 6.9 12.7 80.3 83.9 5.7 89.6

2 34.5 7.4 7.0 9.8 4.0 4.0 66.7 91.7 5.9 97.6

3 16.9 18.1 17.0 3.1 7.9 4.9 67.9 94.7 0 94.74 16.0 18.8 4.0 9.4 4.4 4.2 56.8 82.9 7.6 90.5

Mean 23.4 15.0 9.1 8.2 5.8 6.4 67.9 88.3 4.8 93.1±SEM ±4.3 ±2.6 ±2.8 ±1.7 ±0.9 ±2.1 ±4.8 ±2.9 ±1.6 ±1.9

___ Lv.

___ os

mg2000

800

400

~------------------~----y..-!'------k---,

I'I

I

48time (h)

2412

0..,............. ... .... ....o 2 4 6

Fig. 4. Cumulative excretion of oxiracetam after intravenous and oral administration of a single dose (2000 mg) in four normal sub­jects. Symbols represent the mean ± SEM.

E. Perucca et al.. Pharmacokinetics of oxiracetam i.v. and oral in volunteers 273

nary excretion rate after oral administrationshowed a pattern very similar to the decline inserum levels after both oral and intravenous dosing(the elevation of the last point was largely due to anunexplicably high value in subject I, as shown inTable IV). Renal clearance values accounted formore than 90% of the total body clearance(Table II).

An estimate of bioavailability from the ratiobetween the drug recovery in urine after oral andintravenous administration yielded a value of73± 6%. This is in excellent agreement with thebioavailability calculated from serum level data(75± 7%).

Adverse effects

No adverse effects were observed.

DISCUSSION

Serum levels profiles, urinary recovery data andmain kinetic parameters (see Tables and Figure 2)showed a relatively small interindividual variabilityafter both oral and intravenous administration.This suggests that the findings may be consideredrepresentative for the type of population studied.

Following intravenous administration, serumoxiracetam levels declined very rapidly during thefirst few hours. A similar pattern was observedafter oral administration: within 10 h of oral dos­ing, serum levels had already declined to aboutone-tenth of the peak values. Thereafter, thedecrease in serum concentration was considerablyslower. Since no blood samples were collected after24 h (this would have caused problems in detectionin view of the very low values already present at24 h), we cannot exclude that the terminal phasewas even slower than estimated. However, anyunderestimation is unlikely to be important in lightof the fact that 90% of the drug had already beeneliminated in urine within 24 h. In other words, theterminal phase beyond 24 h contributes little to theoverall removal of drug from the body. Underthese conditions, it is possible that oxiracetam kin­etics could be better explained in terms of a morecomplex model (e.g., a three-compartment model).However, a reliable characterization of this modelwill require more frequent sampling than used inthis study.

In view of the above considerations, the par­ameters derived from the non-compartmental anal­ysis may provide a more useful estimate of the kin-

etic properties of the drug (9,11,12). The mean resi­dence time, which is an indication of the averagepersistence time of drug molecules in the body, wasapproximately 5 h. A volume of distribution (Vda_rea) of approximately 1.2 l-kg! indicates consider­able penetration in the extravascular tissues; how­ever, the volume of distribution at steady state(Vdss) was appreciably smaller (0.6 I·kg-I) . Thislatter parameter, which can be determined withoutthe assumption of a specific compartment model(9), was originally defined by Riggs (10), withrespect to the two-compartment model, as the totalquantity of drug in the body divided by the concen­tration in the reference region of the central com­partment when the concentration in the tissue com­partment is at its maximum.

Oxiracetam was mainly (> 90%) excretedunchanged in urine. It is noteworthy that the renalclearance was approximately equal to the physio­logical value of glomerular filtration and variedvery little among individuals. The fact that renalclearance approached total body clearance indi­cates that extrarenal routes of elimination are virtu­ally negligible and that no first-pass effect is antic­ipated.

These considerations are further supported bythe results of the oral study. Oxiracetam was read­ily absorbed from the gastrointestinal tract. Afterreaching a peak at about I h, serum levels declinedrapidly during the next 7-9 h and more slowlythereafter; almost 50% of the administered dosecould be recovered unchanged in the urine duringthe first 6 h. Estimates of oral availability by twoindependent sets of data (urinary recovery andareas under the serum level-time curve) were inexcellent agreement and indicated that the fractionabsorbed is high (on the average, about 75%).

In conclusion, this study demonstrated that oxi­racetam is well absorbed from the gastrointestinaltract, undergoes relatively extensive distribution inextravascular spaces, and is fairly rapidly elimi­nated - 90% of an intravenous dose was recoveredunchanged in urine within 24 h. Further studies arerequired to characterize in greater detail the drugdisposition in relation to more complex multicom­partmental models. Studies are also required toevaluate any pharmacokinetic change in advancedage and to assess the relationship between single ­and multiple - dose kinetics.

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274 European Journal of Drug Metabolism and Pharmacokinetics. 1984. No 3

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