Epilepsiu , I8(Z), 1911. Raven Press. New York
Clinical Pharmacological Aspects of Valproate Sodium Karl Wulff, Helga Flachs, Annelise Wurtz-Jqrgensen, and Lennart Gram Epilepsy Departments und Lahoratorv, Tlw Filadclfia Colony, Dianalund. Denmurk
VPA is rapidly absorbed after oral administration. The peak concentration in man is rneasValproate sodium (VPA) was introduced as an urable within the initial 1-4 hr (Loiseau et al., antiepileptic drug in 1963 and, owing to its an- 197.5). Simultaneous intake of food will delay abtiepileptic properties, has since found a wide ap- sorption (Meinardi et al., 1975). The biological plication throughout the world. The kinetics im- half-life h a s been found t o c o v e r 8-15 hr plied in the compound have been tested in ani- (Loiseau et al., 1975; Schobben et al., 1975). mal experiments and described in a series of Owing to the relatively short half-life and the papers (Eymard et al., 1971; Kukino and Mat- rapid absorption, the daily fluctuations in consumoto, 1971; Kuhara and Matsumoto, 1974; c e n t r a t i o n s of VPA in s e r u m a r e marked Schobben and van der Kleijn, 1974b). Reports o n (Loiseau et al., 1975; Schobben et al., 1975). human-pharmacological s t u d i e s a r e f e w It has not yet been possible to isolate metabo(Loiseau et al., 1975; Schobben et al., 1975). lites from VPA in man, but identification of such The mode of action of VPA remains to be de- metabolites has been attempted in animal experfined, but its anticonvulsive effect is assumed to iments (Kukino and Matsumoto, 1971; Kuhara be centrally conditioned. Studies of mice and and Matsumoto, 1974; Schobben and van der rats have shown that VPA inhibits gamrna- Kleijn, 1974h). It can hardly be doubted, howaminobutyricacid (GABA) transferase (Simler et e v e r , t h a t t h e d e g r e e t o which VPA is al., 1973; Ferrandes et al., 1974); and succinic- metabolized is considerable since only minor semi-aldehyde dehydrogenase (Sawaya et al., quantities of the drug in nontransformed form 1975), two enzymes of importance for GABA can be recovered from human urine (Schobben catabolism in t h e brain. It h a s b e e n d e m - and van der Kleijn, 1975). Protein binding has onstrated that an increased concentration of been found to be negligible (Schobben and van GABA in the brain of rats protects the latter der Kleijn, 1 9 7 4 ~ ) . against seizures (Godin et al., 1969). It cannot be Correlation between daily dose (mgikg) and precluded that the anticonvulsive action is due attained concentration of VPA in serum has to one o r several metabolites (Schobben and van been found to be poor (Schobben and van der der Kleijn, 1 9 7 4 ~ ) . Kleijn, 1975). The therapeutic level is stated to range between 300 and 600 pmolesiliter (SO- 100 mg/liter) (Loiseau et al., 1975; Schobben and Received September 2 1, 1976. van der Kleijn, 1974u), but no data on the time at Key words: Valproic acid -Protein-bound fraction which blood samples had been drawn are given. - CSF fraction - Daily ,fluctuations - Biologicul Parallel with a clinical trial carried out in our half-life - Clinical c:ffc.ctladvrrse rractionslserurn departments with a view to evaluating the anlevels. INTRODUCTION
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tiepileptic properties of VPA (Gram et al., 1977), a series of pharmacokinetic parameters were examined, e.g., the correlation between daily dose and concentration in serum during steadystate, the daily fluctuations in concentrations of VPA in serum, the half-life after “chronic treatment,” the protein binding, and the ratio of VPA levels in cerebrospinal fluid (CSF) to levels in serum. Furthermore, in a series of healthy subjects receiving single doses of VPA, an attempt has been made to determine the drug’s half-life. PATIENTS AND METHODS Thirty-five hospitalized patients with therapy-resistant epilepsy gave their informed consent to participate in the clinical trial. The age of patients ranged from 8 to 63 years. VPA was administered in the form of 300-mg tablets, the daily dosage being equivalent to 20-25 mg/kg body weight; it was given in four daily doses. After a stepping-up period, the concentration of VPA in serum was assessed at least every 2 weeks for 2 months. All samples were drawn before the morning dose was administered. Another 7 patients in the age group 6-62 years, 2 males and 5 females, were selected, in whom the apparent half-life of V P 4 in serum was determined after chronic treatment. In addition, the ratio of concentration of VPA in CSF to serum concentrations was assessed. In order to determine the half-life after ingestion of a single dose, 6 healthy, fasting volunteers, 1 male and 5 females, in the age group 22-55 years were selected, who at the time t = 0 ingested 600 mg VPA. Five male patients, 17-46 years of age, were singled out in order to determine the intraindividual day-to-day variation in serum VPA levels.
the time t = 0, 40, 60, 75, 90, 1 15, and 130 min, and 6 , 9 , 12, and 24 hr after ingestion of the dose. Determination of the concentration of VPA in CSF included coincident drawing of CSF via lumbar puncture and of blood via venipuncture. This combined sampling was accomplished after the morning dose of VPA had been given. Determination of Concentrations of VPA in Serum and CSF The concentration of VPA was determined by gas-liquid chromatography according to Schobben and van der Kleijn (1974~)and modified by the present authors. The degree of protein binding was assessed by means of Amicon’s CentrifloS cones.
RESULTS Examination of healthy volunteers showed that the half-life of VPA was 8, 9, 10, 10, 11, and 15 hr, respectively (Fig. I). Peak concentrations were attained within 40, 40, 50, 70, 80, and 90 min, respectively. After chronic treatment of 2 patients, the halflife of VPA was found to be 8 and 10 hr, respectively. Both patients received VPA and phenytoin. Figures 2 and 3 show the daily fluctuations in serum concentrations of VPA in 2 patients. The results obtained by coincident assessment of the concentrations of VPA in serum and in CSF in 3 patients are seen in Table I . The protein binding was determined in 14 patients who received chronic treatment. It was found to range between 84 and 95%, median 91.2%. The 35 patients who participated in the clinical trial were classified into five groups according to clinical effects in the form of changed incidence Sampling of seizures (cf. Gram et al., 1977). Table 2 illusThe daily fluctuation of VPA was determined trates the correlation between clinical effect and by means of a permanently introduced intraven- concentration of VPA in serum. Figures 4-8 ilous VenflonO cannula; samples were drawn lustrate, in relation to the above classification, hourly throughout 24 hr. The half-life after the course of concentrations of VPA in serum chronic treatment was also determined via a during the steady-state in the individual patients. permanently introduced intravenous cannula, It appears from the figures that there was no and samples were drawn at the time f = 0, ?h, correlation between attained concentration in I % , 2, 2%, 3, 4, 6, 10, 14, 18, 25, 40, S O , and72 serum and clinical effect, a fact that could be hr after the last dose of VPA had been given. statistically verified (Spearman’s rho, p > 0.10). Chronic treatment was defined as treatment Any systematic variations in serum concentrations of VPA were not demonstrable (Friedman throughout at least 3 weeks. With a view to evaluating the half-life after test p > 0.10). It appears also from the figures ingestion of a single dose, blood was drawn at that concentrations of VPA might vary to a cer-
CLINICAL PHARMACOLOGY OF V P A
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DPA IN SERUM (prnol/l)
t
2
4
6
10
8
12
14
16
18
20
22
24
HOURS
FIG. 1. Serum levels of VPA (DPA) in 6 healthy subjects receiving a single dose of 600 mg VPA
800
700 600
500 400 300 200 100
12
A
300 mg DPA
14
16
A
18
600 mg DPA 200 mg DPH
20
22
A
00
6 0 0 m g DPA 2 5 0 m g Primidone
02
04
06
08
A
10
12
TIME
3 0 0 m g DPA
100 mg DPH 2 5 0 m g Primidone
FIG. 2. Fluctuations in serum levels of VPA (DPA) during 24 hr in a patient treated with 1800 mg of VPA, 300 rng phenytoin (DPH), and 500 mg primidone (Mysolinem) per day.
K . WULFF ET AL.
152 DPA IN SERUM
(ymolll)
I
900
300
200 100
Pb
/
DPH
14
16
A
18
20
300 my DPA
22
A
00
02
600 mg DPA
04
10 6OOmyDPA
50my
Pb 1 5 0 m g DPH
A
12
14
16
TIME
3 0 0 m g DPA
3 0 0 r n y DPA 3 0 m a Pb 100 rn; OPH
FIG. 3. Fluctuations in serum levels of VPA (DPA) during 24 hr in a patient treated with 2,100 mg VPA, 250 rng phenytoin (DPH), and 80 mg phenobarbital (Pb) per day.
tain degree in some of the patients even though dosages were maintained at a constant level and blood samples, as far as possible, always were drawn at the same time of day while the usual treatment was maintained constant (see Gram et al., 1977). Figure 9 illustrates the pronounced variation in concentrations of VPA in 31 patients who received VPA i n doses (rngikg) of nearly identical sizes.
DISCUSSION The half-lives observed in the present study are in complete agreement with those reported in the literature. There is apparently no difference in half-lives of VPA in healthy subjects and in patients who for some time have received the drug while also receiving phenytoin. The concentration of VPA in CSF seems to agree fairly well with concentrations of the free fraction of VPA in serum and with the values
TABLE 1. Siniriltantwus V P A Irrvls i n serum and C S F in 3 prrfienfs Patient Age (years) 8 16
h
VPA serum level
Dose (rngikg) 29 35 31
(prnolesiliter) (rngiliter) I74 200 444
29 33 74
VPA C S F level (prnolesiliter) (rngiliter) 36 21 54
6 3.5 9
CLINICAL PHARMACOLOGY OF VPA TABLE 2. Plasma concentrutions of VPA in relation to ruting of clinical r f f c t Serum-VPA (pmoles/liter) Results I. Excellent 11. Good 111. Moderate IV. Nil V. Aggravation
Median
Range
194 236 I74
105-280 85-315 140-270 140-315 85-340
181
160
I. More than 66% reduction in number of seizures. 11. Between 50% and 66% reduction in number of seizures. 111. Between 33% and 49% reduction in number of seizures. IV. N o substantial change in number of seizures. V. More than 33% increase in number of seizures.
specified in various publications (Meijer and Hessing-Brand, 1973). I t should be noted, however, that the concentration of VPA in CSF is not presumed to parallel the daily fluctuations in concentrations of VPA in serum, the former being by far more constant (van der Kleijn et al., 1975). Accordingly, the concentration of the free fraction of VPA in serum cannot be directly calculated on the basis of the ratio of VPA concentrations in CSF to concentrations in serum, as has been attempted in the case of other antiepileptic agents. The marked fluctuations in concentrations of VPA in serum within 24 hr, apparent from the curve the profile of which emerges from the frequency at which d o s e s a r e given, a r e conditioned by the rapid absorption and the relatively short half-life. The patients comprising the present series received VPA in four daily doses, in fact the lowest acceptable number of doses. It would be desirable if VPA were available in the form of slow-release tablets. Such tablets have actually been produced, although so far only on an experimental basis, and one report has been published (Sonnen et al., 1975). Owing to the considerable daily fluctuations, it is necessary to standardize the time at which samples are to be drawn. Blood samples should preferably be drawn at a time when the change in concentration of VPA in serum is at a minimum, i.e., immediately before ingestion of the morning dose. In the present trial we have tried to standardize, as far as possible, the times at which d o s e s w e r e given a n d blood samples w e r e drawn. Even so, the variations in serum con-
153
centrations of VPA from one sample to another were found to be considerable in some of the patients. Other authors (Loiseau et al., 1975) report a wide variation in serum VPA level from one day to the next in patients on a constant dose of VPA. An actual great variation would suggest that it is absurd to try to monitor VPA by estimating drug levels. To elucidate this observation further, we undertook the following study: 5 epileptic inpat i e n t s , r a n d o m l y c h o s e n , on a c h r o n i c polytherapy including a fixed dose of VPA, had a blood sample drawn "routinely" before the morning dose each day for 5 days. The determination of the serum VPA levels showed a moderate intraindividual coefficient of variation, the mode being k 5% (range 2 5 - i 11%). This result indicates that an essential condition is fulfilled for monitoring VPA by measuring drug levels. That is, through the use of a standard procedure for timing the blood sampling, patients on a constant dose of VPA will produce stable drug levels. In addition, the attained serum concentration was found to vary to a considerable extent in the patients participating in the controlled trial alhough doses of VPA per kilogram of body veight were almost identical. Whether or not there is a correlation between dose and attained level in serum has been the subject of conflicting opinions. Some authors have observed such correlation (Ferrandes and Eymard, 1973) while o t h e r s have been unable t o demonstrate it (Meijer et al., 1973; Schobben et al., 1975). One explanation of the discrepancy may be that the patients concerned had been treated with different antiepileptic agents in different combina; tions. Indeed, further research in this field is needed. In accordance with the findings obtained by Meinardi et al. (1974), no correlation between concentrations of VPA in serum and its clinical effect was observed in the present trial and the same applies to a correlation between concentrations in serum and adverse reactions (MannWhitney test, p > 0.10). It was observed in the clinical routine that the concentration of VPA in serum ranged between 140 and 350 pmolesiliter (23-58 mgiliter) in 85% of the patients who received doses of 20-25 mgikg. In random samples obtained after ingestion of the morning dose, it was found to range from 300 pmolesiliter (50 mgiliter) upward, which is fairly consistent
K . WULFF ET A L
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400
300
200
0
2
4
6
8
WEEKS
FIG. 4. Serum levels of VPA (DPA) in 8 patients in whom the clinical effect was excellent.
DPA I N S E R U M (prnoI/I) 400
T
3 00 200 100
0
2
4
6
8
WEEKS
FIG. 5. Serum levels of VPA (DPA) in 6 patients in whom the clinical effect was good.
DPA IN S E R U M 400
I
300 200
(yrnol/l)
*-
loo/ 0
2
4
6
8
WEEKS
FIG. 6. Serum levels of VPA (DPA) in 7 patients in whom the clinical effect was moderafr.
CLINICAL PHARMACOLOGY OF VPA
155
DPA IN S E R U M (pmoI/l) 400
A
300
1
0
2
4
6
8
WEEKS
FIG. 7. Serum levels of VPA (DPA) in 7 patients in whom no clinical effect occurred.
DPA IN S E R U M (,umol/I)
300 200
100
0
2
4
6
8
WEEKS
FIG. 8. Serum levels of VPA (DPA) in 7 patients in whom a clinical aggruvnrion was observed.
with the therapeutic level reported by Loiseau et al. (1975) and by Schobben and van der Kleijn (1974~).Hence, it can hardly be doubted that blood samples had been drawn from the patients concerned after they had ingested the morning dose. Since a fixed dose per kilogram of body weight was used throughout the present trial and since doses were not adjusted according to effect, we do not consider ourselves competent to establish reliably the range of a therapeutic level. SUMMARY A series of clinical-pharmacological parameters implied in the compound valproate sodium (VPA) have been studied, e.g., the correlation
between daily doses and attained serum concentrations of the drug during the steady state, the daily fluctuations in concentrations of VPA in serum, the half-life of VPA after chronic treatment of patients, the degree of protein binding, and the ratio of VPA concentration in CSF to its concentration in serum. In addition, calculation of the half-life of VPA after administration of a single dose to healthy volunteers has been attempted. In continuation of a controlled clinical trial where VPA was tested as an antiepileptic drug (Gram et al., 1977), the possibility of a correlation between the attained concentrations of VPA in serum and the clinical effects, including the adverse reactions, was evaluated. The half-life was calculated to range between 8 and 10 hr, respectively, in patients whereas in healthy
K . WULFF ET A L .
156 D P A i n serum pmolil
n 31 40
. .. . . . .. . . . . ... . .. . . .. a
30
0
0
0
201
.
0
0
0
10
D o s e of DPA
10
20
30 mq/kg
’
FIG. 9. VPA (DPA) serum levels to dose of VPA (mgikg) in 31 patients.
subjects it was found to be 8, 9, 10, 10, 11, and 15 hr. The ratio of VPA concentrations in CSF to concentrations in serum was determined. In patients, the protein binding was found to range from 84 to 95%. Notwithstanding that doses of VPA per kilogram of body weight were almost identical, its concentration in serum varied appreciably in the patients participating in the present trial. Any correlation between clinical effect, including the adverse reactions, and concentrations of VPA in serum was not demonstrable. In patients, the daily fluctuations in serum concentrations of VPA were pronounced throughout, although VPA was administered in four daily doses. Standardization of the time at which doses are given and blood samples drawn seems to be essential. REFERENCES Eymard P, Simiand J , Teoule R, Poverelli M, Werbenec JP, and Broll M. Etude la rkpartition et de la resorption du dipropylacktate de sodium marque au 14C chez le rat. J Pharmutol (Paris) 2:359-368, 1971.
Ferrandes B and Eymard P. Methode rapitie d’an;ilyse quantitative d u dipropylac-ktate de sodium dam le serum ou le plasma. Ann Phurm Fr 31:279-282, 1973. Ferrandes B, Cohen-Addad C , Benoit-Guyod JL. and Mandel P. Etude des relations entre la structure cristaline et I’activitk biologique de molecules des series di- et trialcoyl acktiques. Biochrm Phurm a d 23:3363-3376, 1974. Gram L, Wulff K, Rasmussen KE, Flachs H. WurtzJsrgensen A, Sommerbeck KW, and Lghren V. Valproate sodium: A controlled clinical trial, including monitoring of serum levels. Epilcpsirr 18: 141-148, 1977. Godin Y , Heiner L, Mark J, and Mandel P. Effects of di-n-propylacetate, an anticonvulsive compound. on GABA metabolism. J Nerrrochem 16:869-873, 1969. van der Kleijn E , Guelen PJM. var der Wijk C, and Baars I. Clinical pharmacokinetics in monitoring chronic medication with antiepileptic drugs. In: H Schneider, D Janz, C Gardner-Thorpe, H Meinardi, and AL Sherwin (Eds), Clinicul Phurnitrcology of Anti-Epileptic Drugs. Springer-Verlag. Berlin. 1975, .. pp 1 1-33, Kuhara T and Matsumoto I . Metabolism of branched medium chain length fatty acid. I-Omega-oxidation
CLINICAL PHARMACOLOGY OF VYA of sodium dipropylacetate in rats. Biomrd M a s s Spectro 1:291-294, 1974. Kukino K and Matsumoto I . Studies on the absorption, excretion and biotransformation of a new anticonvulsant drug, dipropylacetic acid. Kurumr Med 34:369-379, 1971. Loiseau P, Brachet A, and Henry P. Concentration of dipropylacetate in plasma. Epifrpsia 16:609-615, 1975. Meijer JWA and Hessing-Brand L . Determination of lower fatty acids, particularly the anti-epileptic dipropyl-acetic acid, in biological materials by means of micro diffusion and gas chromatography. Clin Chem Actu 43:215-222, 1973. Meinardi H, Hanke NFJ, and van Beveren J. Sodium di-n-propylacetate: Estimation of effective serum levels. Phorm Waekbl 109:45-47, 1974. Meinardi H, van der Kleijn E, Meijer JWA, and van Rees H. Absorption and distribution of antiepileptic drugs. Epikpsiu 16:353-365, 1975. Sawaya MCB, Horton RW, and Meldrum BS. Effects of anticonvulsant drugs on the cerebral enzymes metabolizing GABA. Epilrpsia 16:649-655, 1975. Schobben F and van der Kleijn E. Determination of sodium di-n-propylacetate in plasma by gas-liquid chromatography. P h a r m W e e k h l l09:30- 33, l97k. Schobben F and van der Kleijn E . Pharmacokinetics of distribution and elimination of sodium di-npropylacetate in mouse and dog. P h w m Weakhl 109~33-42, 1 9 7 4 . Schobben F, van der Kleijn E, and Gabreels FJM. Pharmacokinetics of di-n-propylacetate in epileptic patients. Eur J Clin Phurmucol 8:97-105, 1975. Simler S, Ciesielski L, Maitre M, Randrianarisoa H, and Mandel P. Effects of sodium ri-dipropylacetate on audiogenic seizures and brain gammaaminobutyric acid level. B i o c h e m P h a r m n c o l 22: I701 1708, 1973. Sonnen AEH, Blom GF. and Meijer JWA. Enteric coated dipropylacetate (Depakinem). I n : H Schneider, D Janz, C Gardner-Thorpe, H Meinardi, AL Sherwin (Eds), Clinic,ul Phurmucology qf Anti-Epilrptic Drugs. Springer-Verlag, Berlin, 1975, pp 229-234. -
RESUME On a CtudiC pour le VPA, une serie de parametres clinico-pharmacologiques, e.g., la corrklation entre les doses journalieres et les concentrations seriques de la substance pendant le steady-state, les variations journalieres des taux striques de VPA, la demi-vie du VPA en traitement chronique, le degre de liaison avec les proteines et le rapport de concentration VPA sCrique et VPA dans le LCR. Par ailleurs on a essay6 de calculer la demi-vie de VPA a p e s une seule prise chez des sujets normaux volontaires. En continuation avec I’essai clinique contra16 dans lequel le VPA Ctait teste comme substance antikpileptique (Gram et al., 1977), on a evalue la possible correlation entre les taux skriques de VPA et les effets cliniques, y compris les effets secondaires. Chez les patients, la demi-vie Ctait de 8 B 10 heures tandis qu’elle variait entre 8, 9, 10, I 1, et 15 heures chez les volontaires normaux. Dans le Tableau 1, sont indiquCs les rapports de VPA driques
157
et LCR. Chez les patients le degrC de liaison proteique C h i t entre 84et 95%J.Bien que les doses de VPNkg de
poids etaient presque identiques, les taux seriques de VPA Ctaient variables. (C. A. Tassinari, Mur.seillc~.s)
RESUMEN Se ha estudiado una serie de parzimetros clinicofarmacol6gicos implicados en el compuesto VPA, como por ejemplo: la correlacibn entre las dosis diarias y las concentraciones de la droga en suero alcanzando durante el steady-state, las fluctuaciones diarias de las concentraciones del VPA en suero, la vida media del VPA tras un tratarniento cr6nico de 10s enfermos, el grado de uni6n a las proteinas y la relaci6n entre las concentraciones del VPA en liquido cefalorraquideo (LCR) y suero. Ademzis se ha intentado calcular la vida media del VPA tras la administracidn de una dosis unica a voluntarios sanos. Como continuacidn a un ensayo clinico controlado en el que el VPA se valor6 como droga antiepikptica (Gram et al., 1977) se estudid si podria existir correlaci6n entre 10s niveles de VPA alcanzando en el suero y 10s resultados clinicos incluidas las reacciones adversas. L a vida media parecia oscilar entre 8 y 10 horas en pacientes mientras que variaba entre 8, 9, 10, 11, y 15 horas en sujetos sanos. La relaci6n entre las concentraciones del VPA en LCR y suero aparece en la Tabla I . En 10s enfermos la uni6n a las proteinas se produjo entre un 84% y u n 95%. A pesar de que las dosis del VPA por kilo de peso eran casi identicas, las concentraciones en suero variaban. (A. Portera Sanchez, Mudrid)
ZUSAMMENFASSUNG Eine Reihe klinisch-pharmakologischer Parameter bei Verabfolgung von Natriumvalprod (VPS) wurden untersucht 2.B.: Die Korrelation zwischen der taglichen Dosis und der Medikamentenkonzentration im Serum wahrend des steady-state, die taglichen Fluktuationen in der Konzentration des VPA im Serum, die Halbwertszeit des VPA nach chronischer Behandlung von Patienten, das AusmaB der Eiweillbindung, das Verhaltnis der Konzentration von VPA im Liquor zu seiner Konzentration im Serum. Zusatzlich wurde versucht die Halbwertszeit von VPA nach Anwendung einer Einzeldosis bei gesunden Freiwilligen zu errechnen. In Fortfuhrung einer kontrollierten klinischen Untersuchung, in der VPA als Antiepileptikum getestet wurde (Gram et al., 1977) wurde untersucht, ob eine Korrelation zwischen der Serumkonzentration des VPA und der klinischen Wirkung einschliel3lich der Nebenwirkungen bestunde. Die Halbwertszeit wurde fur Patienten zwischen 8 und 10 Stunden err e c h n e t , wahrend gesunde Probanden eine Halbwertszeit von 8, 9, 10, 1 1 , und IS Stunden zeigten. Das Konzentrationsverhaltnis der VPA zwischen Liquor und Serum gibt Tabelle 1 wieder. Die Eiweillbindung betrug bei Patienten zwischen 84 und 95%. Ungeachtet der Tatsache, dal) die VPA-Dosen je kglKorpergewicht weitgehend identisch waren, zeigten sich Unterschiede in der Serumkonzentration. (D. Scheffner, H e i d e l h u g )
Clinical Pharmacological Aspects of Valproate Sodium Karl Wulff, Helga Flachs, Annelise Wurtz-Jqrgensen, and Lennart Gram Epilepsy Departments und Lahoratorv, Tlw Filadclfia Colony, Dianalund. Denmurk
VPA is rapidly absorbed after oral administration. The peak concentration in man is rneasValproate sodium (VPA) was introduced as an urable within the initial 1-4 hr (Loiseau et al., antiepileptic drug in 1963 and, owing to its an- 197.5). Simultaneous intake of food will delay abtiepileptic properties, has since found a wide ap- sorption (Meinardi et al., 1975). The biological plication throughout the world. The kinetics im- half-life h a s been found t o c o v e r 8-15 hr plied in the compound have been tested in ani- (Loiseau et al., 1975; Schobben et al., 1975). mal experiments and described in a series of Owing to the relatively short half-life and the papers (Eymard et al., 1971; Kukino and Mat- rapid absorption, the daily fluctuations in consumoto, 1971; Kuhara and Matsumoto, 1974; c e n t r a t i o n s of VPA in s e r u m a r e marked Schobben and van der Kleijn, 1974b). Reports o n (Loiseau et al., 1975; Schobben et al., 1975). human-pharmacological s t u d i e s a r e f e w It has not yet been possible to isolate metabo(Loiseau et al., 1975; Schobben et al., 1975). lites from VPA in man, but identification of such The mode of action of VPA remains to be de- metabolites has been attempted in animal experfined, but its anticonvulsive effect is assumed to iments (Kukino and Matsumoto, 1971; Kuhara be centrally conditioned. Studies of mice and and Matsumoto, 1974; Schobben and van der rats have shown that VPA inhibits gamrna- Kleijn, 1974h). It can hardly be doubted, howaminobutyricacid (GABA) transferase (Simler et e v e r , t h a t t h e d e g r e e t o which VPA is al., 1973; Ferrandes et al., 1974); and succinic- metabolized is considerable since only minor semi-aldehyde dehydrogenase (Sawaya et al., quantities of the drug in nontransformed form 1975), two enzymes of importance for GABA can be recovered from human urine (Schobben catabolism in t h e brain. It h a s b e e n d e m - and van der Kleijn, 1975). Protein binding has onstrated that an increased concentration of been found to be negligible (Schobben and van GABA in the brain of rats protects the latter der Kleijn, 1 9 7 4 ~ ) . against seizures (Godin et al., 1969). It cannot be Correlation between daily dose (mgikg) and precluded that the anticonvulsive action is due attained concentration of VPA in serum has to one o r several metabolites (Schobben and van been found to be poor (Schobben and van der der Kleijn, 1 9 7 4 ~ ) . Kleijn, 1975). The therapeutic level is stated to range between 300 and 600 pmolesiliter (SO- 100 mg/liter) (Loiseau et al., 1975; Schobben and Received September 2 1, 1976. van der Kleijn, 1974u), but no data on the time at Key words: Valproic acid -Protein-bound fraction which blood samples had been drawn are given. - CSF fraction - Daily ,fluctuations - Biologicul Parallel with a clinical trial carried out in our half-life - Clinical c:ffc.ctladvrrse rractionslserurn departments with a view to evaluating the anlevels. INTRODUCTION
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f 50
K . WULFF ET A L .
tiepileptic properties of VPA (Gram et al., 1977), a series of pharmacokinetic parameters were examined, e.g., the correlation between daily dose and concentration in serum during steadystate, the daily fluctuations in concentrations of VPA in serum, the half-life after “chronic treatment,” the protein binding, and the ratio of VPA levels in cerebrospinal fluid (CSF) to levels in serum. Furthermore, in a series of healthy subjects receiving single doses of VPA, an attempt has been made to determine the drug’s half-life. PATIENTS AND METHODS Thirty-five hospitalized patients with therapy-resistant epilepsy gave their informed consent to participate in the clinical trial. The age of patients ranged from 8 to 63 years. VPA was administered in the form of 300-mg tablets, the daily dosage being equivalent to 20-25 mg/kg body weight; it was given in four daily doses. After a stepping-up period, the concentration of VPA in serum was assessed at least every 2 weeks for 2 months. All samples were drawn before the morning dose was administered. Another 7 patients in the age group 6-62 years, 2 males and 5 females, were selected, in whom the apparent half-life of V P 4 in serum was determined after chronic treatment. In addition, the ratio of concentration of VPA in CSF to serum concentrations was assessed. In order to determine the half-life after ingestion of a single dose, 6 healthy, fasting volunteers, 1 male and 5 females, in the age group 22-55 years were selected, who at the time t = 0 ingested 600 mg VPA. Five male patients, 17-46 years of age, were singled out in order to determine the intraindividual day-to-day variation in serum VPA levels.
the time t = 0, 40, 60, 75, 90, 1 15, and 130 min, and 6 , 9 , 12, and 24 hr after ingestion of the dose. Determination of the concentration of VPA in CSF included coincident drawing of CSF via lumbar puncture and of blood via venipuncture. This combined sampling was accomplished after the morning dose of VPA had been given. Determination of Concentrations of VPA in Serum and CSF The concentration of VPA was determined by gas-liquid chromatography according to Schobben and van der Kleijn (1974~)and modified by the present authors. The degree of protein binding was assessed by means of Amicon’s CentrifloS cones.
RESULTS Examination of healthy volunteers showed that the half-life of VPA was 8, 9, 10, 10, 11, and 15 hr, respectively (Fig. I). Peak concentrations were attained within 40, 40, 50, 70, 80, and 90 min, respectively. After chronic treatment of 2 patients, the halflife of VPA was found to be 8 and 10 hr, respectively. Both patients received VPA and phenytoin. Figures 2 and 3 show the daily fluctuations in serum concentrations of VPA in 2 patients. The results obtained by coincident assessment of the concentrations of VPA in serum and in CSF in 3 patients are seen in Table I . The protein binding was determined in 14 patients who received chronic treatment. It was found to range between 84 and 95%, median 91.2%. The 35 patients who participated in the clinical trial were classified into five groups according to clinical effects in the form of changed incidence Sampling of seizures (cf. Gram et al., 1977). Table 2 illusThe daily fluctuation of VPA was determined trates the correlation between clinical effect and by means of a permanently introduced intraven- concentration of VPA in serum. Figures 4-8 ilous VenflonO cannula; samples were drawn lustrate, in relation to the above classification, hourly throughout 24 hr. The half-life after the course of concentrations of VPA in serum chronic treatment was also determined via a during the steady-state in the individual patients. permanently introduced intravenous cannula, It appears from the figures that there was no and samples were drawn at the time f = 0, ?h, correlation between attained concentration in I % , 2, 2%, 3, 4, 6, 10, 14, 18, 25, 40, S O , and72 serum and clinical effect, a fact that could be hr after the last dose of VPA had been given. statistically verified (Spearman’s rho, p > 0.10). Chronic treatment was defined as treatment Any systematic variations in serum concentrations of VPA were not demonstrable (Friedman throughout at least 3 weeks. With a view to evaluating the half-life after test p > 0.10). It appears also from the figures ingestion of a single dose, blood was drawn at that concentrations of VPA might vary to a cer-
CLINICAL PHARMACOLOGY OF V P A
151
DPA IN SERUM (prnol/l)
t
2
4
6
10
8
12
14
16
18
20
22
24
HOURS
FIG. 1. Serum levels of VPA (DPA) in 6 healthy subjects receiving a single dose of 600 mg VPA
800
700 600
500 400 300 200 100
12
A
300 mg DPA
14
16
A
18
600 mg DPA 200 mg DPH
20
22
A
00
6 0 0 m g DPA 2 5 0 m g Primidone
02
04
06
08
A
10
12
TIME
3 0 0 m g DPA
100 mg DPH 2 5 0 m g Primidone
FIG. 2. Fluctuations in serum levels of VPA (DPA) during 24 hr in a patient treated with 1800 mg of VPA, 300 rng phenytoin (DPH), and 500 mg primidone (Mysolinem) per day.
K . WULFF ET AL.
152 DPA IN SERUM
(ymolll)
I
900
300
200 100
Pb
/
DPH
14
16
A
18
20
300 my DPA
22
A
00
02
600 mg DPA
04
10 6OOmyDPA
50my
Pb 1 5 0 m g DPH
A
12
14
16
TIME
3 0 0 m g DPA
3 0 0 r n y DPA 3 0 m a Pb 100 rn; OPH
FIG. 3. Fluctuations in serum levels of VPA (DPA) during 24 hr in a patient treated with 2,100 mg VPA, 250 rng phenytoin (DPH), and 80 mg phenobarbital (Pb) per day.
tain degree in some of the patients even though dosages were maintained at a constant level and blood samples, as far as possible, always were drawn at the same time of day while the usual treatment was maintained constant (see Gram et al., 1977). Figure 9 illustrates the pronounced variation in concentrations of VPA in 31 patients who received VPA i n doses (rngikg) of nearly identical sizes.
DISCUSSION The half-lives observed in the present study are in complete agreement with those reported in the literature. There is apparently no difference in half-lives of VPA in healthy subjects and in patients who for some time have received the drug while also receiving phenytoin. The concentration of VPA in CSF seems to agree fairly well with concentrations of the free fraction of VPA in serum and with the values
TABLE 1. Siniriltantwus V P A Irrvls i n serum and C S F in 3 prrfienfs Patient Age (years) 8 16
h
VPA serum level
Dose (rngikg) 29 35 31
(prnolesiliter) (rngiliter) I74 200 444
29 33 74
VPA C S F level (prnolesiliter) (rngiliter) 36 21 54
6 3.5 9
CLINICAL PHARMACOLOGY OF VPA TABLE 2. Plasma concentrutions of VPA in relation to ruting of clinical r f f c t Serum-VPA (pmoles/liter) Results I. Excellent 11. Good 111. Moderate IV. Nil V. Aggravation
Median
Range
194 236 I74
105-280 85-315 140-270 140-315 85-340
181
160
I. More than 66% reduction in number of seizures. 11. Between 50% and 66% reduction in number of seizures. 111. Between 33% and 49% reduction in number of seizures. IV. N o substantial change in number of seizures. V. More than 33% increase in number of seizures.
specified in various publications (Meijer and Hessing-Brand, 1973). I t should be noted, however, that the concentration of VPA in CSF is not presumed to parallel the daily fluctuations in concentrations of VPA in serum, the former being by far more constant (van der Kleijn et al., 1975). Accordingly, the concentration of the free fraction of VPA in serum cannot be directly calculated on the basis of the ratio of VPA concentrations in CSF to concentrations in serum, as has been attempted in the case of other antiepileptic agents. The marked fluctuations in concentrations of VPA in serum within 24 hr, apparent from the curve the profile of which emerges from the frequency at which d o s e s a r e given, a r e conditioned by the rapid absorption and the relatively short half-life. The patients comprising the present series received VPA in four daily doses, in fact the lowest acceptable number of doses. It would be desirable if VPA were available in the form of slow-release tablets. Such tablets have actually been produced, although so far only on an experimental basis, and one report has been published (Sonnen et al., 1975). Owing to the considerable daily fluctuations, it is necessary to standardize the time at which samples are to be drawn. Blood samples should preferably be drawn at a time when the change in concentration of VPA in serum is at a minimum, i.e., immediately before ingestion of the morning dose. In the present trial we have tried to standardize, as far as possible, the times at which d o s e s w e r e given a n d blood samples w e r e drawn. Even so, the variations in serum con-
153
centrations of VPA from one sample to another were found to be considerable in some of the patients. Other authors (Loiseau et al., 1975) report a wide variation in serum VPA level from one day to the next in patients on a constant dose of VPA. An actual great variation would suggest that it is absurd to try to monitor VPA by estimating drug levels. To elucidate this observation further, we undertook the following study: 5 epileptic inpat i e n t s , r a n d o m l y c h o s e n , on a c h r o n i c polytherapy including a fixed dose of VPA, had a blood sample drawn "routinely" before the morning dose each day for 5 days. The determination of the serum VPA levels showed a moderate intraindividual coefficient of variation, the mode being k 5% (range 2 5 - i 11%). This result indicates that an essential condition is fulfilled for monitoring VPA by measuring drug levels. That is, through the use of a standard procedure for timing the blood sampling, patients on a constant dose of VPA will produce stable drug levels. In addition, the attained serum concentration was found to vary to a considerable extent in the patients participating in the controlled trial alhough doses of VPA per kilogram of body veight were almost identical. Whether or not there is a correlation between dose and attained level in serum has been the subject of conflicting opinions. Some authors have observed such correlation (Ferrandes and Eymard, 1973) while o t h e r s have been unable t o demonstrate it (Meijer et al., 1973; Schobben et al., 1975). One explanation of the discrepancy may be that the patients concerned had been treated with different antiepileptic agents in different combina; tions. Indeed, further research in this field is needed. In accordance with the findings obtained by Meinardi et al. (1974), no correlation between concentrations of VPA in serum and its clinical effect was observed in the present trial and the same applies to a correlation between concentrations in serum and adverse reactions (MannWhitney test, p > 0.10). It was observed in the clinical routine that the concentration of VPA in serum ranged between 140 and 350 pmolesiliter (23-58 mgiliter) in 85% of the patients who received doses of 20-25 mgikg. In random samples obtained after ingestion of the morning dose, it was found to range from 300 pmolesiliter (50 mgiliter) upward, which is fairly consistent
K . WULFF ET A L
154
400
300
200
0
2
4
6
8
WEEKS
FIG. 4. Serum levels of VPA (DPA) in 8 patients in whom the clinical effect was excellent.
DPA I N S E R U M (prnoI/I) 400
T
3 00 200 100
0
2
4
6
8
WEEKS
FIG. 5. Serum levels of VPA (DPA) in 6 patients in whom the clinical effect was good.
DPA IN S E R U M 400
I
300 200
(yrnol/l)
*-
loo/ 0
2
4
6
8
WEEKS
FIG. 6. Serum levels of VPA (DPA) in 7 patients in whom the clinical effect was moderafr.
CLINICAL PHARMACOLOGY OF VPA
155
DPA IN S E R U M (pmoI/l) 400
A
300
1
0
2
4
6
8
WEEKS
FIG. 7. Serum levels of VPA (DPA) in 7 patients in whom no clinical effect occurred.
DPA IN S E R U M (,umol/I)
300 200
100
0
2
4
6
8
WEEKS
FIG. 8. Serum levels of VPA (DPA) in 7 patients in whom a clinical aggruvnrion was observed.
with the therapeutic level reported by Loiseau et al. (1975) and by Schobben and van der Kleijn (1974~).Hence, it can hardly be doubted that blood samples had been drawn from the patients concerned after they had ingested the morning dose. Since a fixed dose per kilogram of body weight was used throughout the present trial and since doses were not adjusted according to effect, we do not consider ourselves competent to establish reliably the range of a therapeutic level. SUMMARY A series of clinical-pharmacological parameters implied in the compound valproate sodium (VPA) have been studied, e.g., the correlation
between daily doses and attained serum concentrations of the drug during the steady state, the daily fluctuations in concentrations of VPA in serum, the half-life of VPA after chronic treatment of patients, the degree of protein binding, and the ratio of VPA concentration in CSF to its concentration in serum. In addition, calculation of the half-life of VPA after administration of a single dose to healthy volunteers has been attempted. In continuation of a controlled clinical trial where VPA was tested as an antiepileptic drug (Gram et al., 1977), the possibility of a correlation between the attained concentrations of VPA in serum and the clinical effects, including the adverse reactions, was evaluated. The half-life was calculated to range between 8 and 10 hr, respectively, in patients whereas in healthy
K . WULFF ET A L .
156 D P A i n serum pmolil
n 31 40
. .. . . . .. . . . . ... . .. . . .. a
30
0
0
0
201
.
0
0
0
10
D o s e of DPA
10
20
30 mq/kg
’
FIG. 9. VPA (DPA) serum levels to dose of VPA (mgikg) in 31 patients.
subjects it was found to be 8, 9, 10, 10, 11, and 15 hr. The ratio of VPA concentrations in CSF to concentrations in serum was determined. In patients, the protein binding was found to range from 84 to 95%. Notwithstanding that doses of VPA per kilogram of body weight were almost identical, its concentration in serum varied appreciably in the patients participating in the present trial. Any correlation between clinical effect, including the adverse reactions, and concentrations of VPA in serum was not demonstrable. In patients, the daily fluctuations in serum concentrations of VPA were pronounced throughout, although VPA was administered in four daily doses. Standardization of the time at which doses are given and blood samples drawn seems to be essential. REFERENCES Eymard P, Simiand J , Teoule R, Poverelli M, Werbenec JP, and Broll M. Etude la rkpartition et de la resorption du dipropylacktate de sodium marque au 14C chez le rat. J Pharmutol (Paris) 2:359-368, 1971.
Ferrandes B and Eymard P. Methode rapitie d’an;ilyse quantitative d u dipropylac-ktate de sodium dam le serum ou le plasma. Ann Phurm Fr 31:279-282, 1973. Ferrandes B, Cohen-Addad C , Benoit-Guyod JL. and Mandel P. Etude des relations entre la structure cristaline et I’activitk biologique de molecules des series di- et trialcoyl acktiques. Biochrm Phurm a d 23:3363-3376, 1974. Gram L, Wulff K, Rasmussen KE, Flachs H. WurtzJsrgensen A, Sommerbeck KW, and Lghren V. Valproate sodium: A controlled clinical trial, including monitoring of serum levels. Epilcpsirr 18: 141-148, 1977. Godin Y , Heiner L, Mark J, and Mandel P. Effects of di-n-propylacetate, an anticonvulsive compound. on GABA metabolism. J Nerrrochem 16:869-873, 1969. van der Kleijn E , Guelen PJM. var der Wijk C, and Baars I. Clinical pharmacokinetics in monitoring chronic medication with antiepileptic drugs. In: H Schneider, D Janz, C Gardner-Thorpe, H Meinardi, and AL Sherwin (Eds), Clinicul Phurnitrcology of Anti-Epileptic Drugs. Springer-Verlag. Berlin. 1975, .. pp 1 1-33, Kuhara T and Matsumoto I . Metabolism of branched medium chain length fatty acid. I-Omega-oxidation
CLINICAL PHARMACOLOGY OF VYA of sodium dipropylacetate in rats. Biomrd M a s s Spectro 1:291-294, 1974. Kukino K and Matsumoto I . Studies on the absorption, excretion and biotransformation of a new anticonvulsant drug, dipropylacetic acid. Kurumr Med 34:369-379, 1971. Loiseau P, Brachet A, and Henry P. Concentration of dipropylacetate in plasma. Epifrpsia 16:609-615, 1975. Meijer JWA and Hessing-Brand L . Determination of lower fatty acids, particularly the anti-epileptic dipropyl-acetic acid, in biological materials by means of micro diffusion and gas chromatography. Clin Chem Actu 43:215-222, 1973. Meinardi H, Hanke NFJ, and van Beveren J. Sodium di-n-propylacetate: Estimation of effective serum levels. Phorm Waekbl 109:45-47, 1974. Meinardi H, van der Kleijn E, Meijer JWA, and van Rees H. Absorption and distribution of antiepileptic drugs. Epikpsiu 16:353-365, 1975. Sawaya MCB, Horton RW, and Meldrum BS. Effects of anticonvulsant drugs on the cerebral enzymes metabolizing GABA. Epilrpsia 16:649-655, 1975. Schobben F and van der Kleijn E. Determination of sodium di-n-propylacetate in plasma by gas-liquid chromatography. P h a r m W e e k h l l09:30- 33, l97k. Schobben F and van der Kleijn E . Pharmacokinetics of distribution and elimination of sodium di-npropylacetate in mouse and dog. P h w m Weakhl 109~33-42, 1 9 7 4 . Schobben F, van der Kleijn E, and Gabreels FJM. Pharmacokinetics of di-n-propylacetate in epileptic patients. Eur J Clin Phurmucol 8:97-105, 1975. Simler S, Ciesielski L, Maitre M, Randrianarisoa H, and Mandel P. Effects of sodium ri-dipropylacetate on audiogenic seizures and brain gammaaminobutyric acid level. B i o c h e m P h a r m n c o l 22: I701 1708, 1973. Sonnen AEH, Blom GF. and Meijer JWA. Enteric coated dipropylacetate (Depakinem). I n : H Schneider, D Janz, C Gardner-Thorpe, H Meinardi, AL Sherwin (Eds), Clinic,ul Phurmucology qf Anti-Epilrptic Drugs. Springer-Verlag, Berlin, 1975, pp 229-234. -
RESUME On a CtudiC pour le VPA, une serie de parametres clinico-pharmacologiques, e.g., la corrklation entre les doses journalieres et les concentrations seriques de la substance pendant le steady-state, les variations journalieres des taux striques de VPA, la demi-vie du VPA en traitement chronique, le degre de liaison avec les proteines et le rapport de concentration VPA sCrique et VPA dans le LCR. Par ailleurs on a essay6 de calculer la demi-vie de VPA a p e s une seule prise chez des sujets normaux volontaires. En continuation avec I’essai clinique contra16 dans lequel le VPA Ctait teste comme substance antikpileptique (Gram et al., 1977), on a evalue la possible correlation entre les taux skriques de VPA et les effets cliniques, y compris les effets secondaires. Chez les patients, la demi-vie Ctait de 8 B 10 heures tandis qu’elle variait entre 8, 9, 10, I 1, et 15 heures chez les volontaires normaux. Dans le Tableau 1, sont indiquCs les rapports de VPA driques
157
et LCR. Chez les patients le degrC de liaison proteique C h i t entre 84et 95%J.Bien que les doses de VPNkg de
poids etaient presque identiques, les taux seriques de VPA Ctaient variables. (C. A. Tassinari, Mur.seillc~.s)
RESUMEN Se ha estudiado una serie de parzimetros clinicofarmacol6gicos implicados en el compuesto VPA, como por ejemplo: la correlacibn entre las dosis diarias y las concentraciones de la droga en suero alcanzando durante el steady-state, las fluctuaciones diarias de las concentraciones del VPA en suero, la vida media del VPA tras un tratarniento cr6nico de 10s enfermos, el grado de uni6n a las proteinas y la relaci6n entre las concentraciones del VPA en liquido cefalorraquideo (LCR) y suero. Ademzis se ha intentado calcular la vida media del VPA tras la administracidn de una dosis unica a voluntarios sanos. Como continuacidn a un ensayo clinico controlado en el que el VPA se valor6 como droga antiepikptica (Gram et al., 1977) se estudid si podria existir correlaci6n entre 10s niveles de VPA alcanzando en el suero y 10s resultados clinicos incluidas las reacciones adversas. L a vida media parecia oscilar entre 8 y 10 horas en pacientes mientras que variaba entre 8, 9, 10, 11, y 15 horas en sujetos sanos. La relaci6n entre las concentraciones del VPA en LCR y suero aparece en la Tabla I . En 10s enfermos la uni6n a las proteinas se produjo entre un 84% y u n 95%. A pesar de que las dosis del VPA por kilo de peso eran casi identicas, las concentraciones en suero variaban. (A. Portera Sanchez, Mudrid)
ZUSAMMENFASSUNG Eine Reihe klinisch-pharmakologischer Parameter bei Verabfolgung von Natriumvalprod (VPS) wurden untersucht 2.B.: Die Korrelation zwischen der taglichen Dosis und der Medikamentenkonzentration im Serum wahrend des steady-state, die taglichen Fluktuationen in der Konzentration des VPA im Serum, die Halbwertszeit des VPA nach chronischer Behandlung von Patienten, das AusmaB der Eiweillbindung, das Verhaltnis der Konzentration von VPA im Liquor zu seiner Konzentration im Serum. Zusatzlich wurde versucht die Halbwertszeit von VPA nach Anwendung einer Einzeldosis bei gesunden Freiwilligen zu errechnen. In Fortfuhrung einer kontrollierten klinischen Untersuchung, in der VPA als Antiepileptikum getestet wurde (Gram et al., 1977) wurde untersucht, ob eine Korrelation zwischen der Serumkonzentration des VPA und der klinischen Wirkung einschliel3lich der Nebenwirkungen bestunde. Die Halbwertszeit wurde fur Patienten zwischen 8 und 10 Stunden err e c h n e t , wahrend gesunde Probanden eine Halbwertszeit von 8, 9, 10, 1 1 , und IS Stunden zeigten. Das Konzentrationsverhaltnis der VPA zwischen Liquor und Serum gibt Tabelle 1 wieder. Die Eiweillbindung betrug bei Patienten zwischen 84 und 95%. Ungeachtet der Tatsache, dal) die VPA-Dosen je kglKorpergewicht weitgehend identisch waren, zeigten sich Unterschiede in der Serumkonzentration. (D. Scheffner, H e i d e l h u g )
