Gas-chromatographic analysis for succinimide anticonvulsants in serum: macro- and micro-scale methods

A gas-chromatographic analysis for the succinimide anticonvulsant drugs--ethosuximide, methsuximide, and phensuximide--in 1.0 ml of serum was modified to improve its reliability, speed, and precision. A separate procedure for 10-100 mul of serum was also developed. Neither method requires an initial preparation of derivatives. The working range of each method is about 10-100 mg/liter for the macro-method, 2-100 mg/liter for the micro-method. The methsuximide metabolite, N-desmethylmethsuximide, is included in both methods. Concentrations of N-desmethylmethsuximide in the blood of two patients with petit mal epilepsy are reported.

Simultaneous quantitative gas-chromatographic analysis of ethosuximide, phenobarbitone, primidone and diphenylhydantoin

1 Therapeutic serum concentrations of ethosuximide, phenobarbitone, primidone, and dipheylhydantoin were assayed from 1 ml of human serum. The extraction procedure was common to all four drugs and three internal standards. 2 Subsequent isothermal gas chromatographic analysis of serum extracts produced well resolved peaks for the underivatized quantitation of ethosuximide and phenobarbitone. Primidone and diphenylhydantoin were determined as methylated derivatives. 3 Mean coefficients of variation for the assay of each drug were less 7% on a newly packed and conditioned column and less than 10% after the technique had been in continuous use for 3 months. 4 The advantage of quantitation relative to peak area ratios rather than peak height ratios was minimal for the determination of ethosuximide, primidone and diphenylhydantoin but appeared significant for the assay of phenobarbitone.

Ethosuximide dosage regimens

A study was conducted in 9 children with petit mal epilepsy to compare the plasma levels of ethosuximide after divided daily administration with those after single daily administration. The children received their previously established dose in divided doses for 4 wk, single morning doses for 4 wk, and again in divided doses for 4 wk. None of the children suffered petit mal seizures during the study. Three had grand mal seizures but the frequency did not differ between the dosage regimens. Plasma levels during the single-dose period peaked more rapidly and fell more quickly than during the other periods, but mean levels remained in the therapeutic range. The mean half-life of the drug in these children was 29 hr. For reasons not understood, plasma levels generally were lower in the second divided dose period than in the other two periods. No adverse experiences were reported during the study. The data indicate that ethosuximide is clinically effective when given in a single daily dose. This regimen offers advantages in convenience and possibly in patient compliance.

Simultaneous high-pressure liquid-chromatographic determination of some anticonvulsants in serum

We describe procedures for simultaneously determining some anticonvulsants (phenobarbital, diphenylhydantoin, primidone, ethosuximide, methsuximide, carbamazepine) in serum by high-pressure liquid chromatography. The drugs, together with an internal standard, phenacetin, are adsorbed from serum onto charcoal and eluted from it with organic solvent. The eluate is analyzed isocratically on a reverse-phase column with a mobile phase consisting of acetonitrile/water (17/83 by volume). The eluted drugs are detected by their absorption at 195 nm, and quantities estimated from their peak areas as compared with those of extracted standards. Results are reproducible to about 6%. Sensitivities, for 0.5-ml serum samples, of 0.1 mg/liter for all the drugs analyzed except ethosuximide (0.5 mg/liter) are attained routinely. Correlation of results with gas chromatography was 0.912 for phenobarbital, 0.982 for diphenylhydantoin, 0.886 for primidone, and 0.966 for ethosuximide. Amobarbital and secobarbital interfere with the analysis; chlordiazepoxide, methaqualone, salicylate, diazepam, and oxazepam do not. Including extraction, analysis time for a single sample is 20 min.

Ethosuximide in the treatment of absence (peptit mal) seizures

Thirty-seven patients with previously untreated absence seizures were treated with ethosuximide. Seizures were completely controlled in 7 patients (19 percent); 90 to 100 percent control was achieved in 18 patients (49 percent) and 50 to 100 percent control in 35 (95 percent). Plasma ethosuximide concentration increased with dose, but variability in the plasma concentration produced by a given ethosuximide dose made it impossible to predict a patient's plasma concentration from the dose. The therapeutic range of plasma ethosuximide concentration was 40 to 100 mug per milliliter. Patients with evidence of structural central nervous system abnormalities responded as well or better to the drug as patients without such evidence. Ethosuximide did not impair psychometric performance, but rather resulted in improved performance in 17 cases. The side effects of ethosuximide were minor, and rarely required withdrawal of the drug.

A quantitative gas chromatographic determination of ethosuximide based on N-butylation

A gas chromatographic procedure has been developed for the routine determination of the anticonvulsant, ethosuximide, in serum. Volatile butyl derivatives for gas chromatography were prepared by the method of R.H. Greeley (J. Chromatogr., 88 (1974) 229) using butyl iodide as the alkylating agent. This procedure yielded stable derivatives with improved chromatographic qualities over those obtained by methylation and proved superior to both on-column alkylation with tetrabutylammonium hydroxide and to silylation. The analysis requires 0.5 ml of serum and the between run precision of the assay at 40 mug/ml was 3.3%.

Gas chromatographic determination of ethosuximide and phensuximide in plasma and urine of man

Ethosuximide and phensuximide in plasma and urine can be assayed to a concentration of 2–5 μg ml−1 by a rapid and specific gas chromatographic assay. The method can be used to monitor plasma concentrations in patients with petit mal treated with these drugs alone or in combination with other antiepileptic drugs. The steady-state plasma concentrations of ethosuximide in children given 10–45 mg kg−1 day−1 varied between 10 and 150 μg ml−1 indicating marked interindividual differences in pharmacokinetics.