Studies on the absorption rate of barbiturates in man

Disposition of anticonvulsants in childhood

There have been great advances in our understanding of the childhood epilepsies within recent years and at the same time there has been increasing awareness of the pharmacokinetic properties of the anticonvulsant drugs. It has been increasingly recognised that pharmacokinetic parameters of anticonvulsants are not constant, but are subject to influences by a number of physiological variables over which age is a major determinant. As changes in pharmacokinetic parameters will alter dosage requirements, dosage regimens cannot be transferred from one age group to another without the risk of underdosing or overdosing. Drug monitoring techniques are being increasingly used as a guide to correct dosing but knowledge of the limitations of monitoring is as important as knowledge of potential benefits for monitoring to be used correctly. An overview of the important pharmacokinetic properties of anticonvulsant drugs is provided, with emphasis on findings in children where such data are available.

Analysis of trace amounts of barbiturates in saliva

A simple gas chromatographic method is presented for the determination of trace quantities (0.1-1.0 microgram/ml) of amobarbital, pentobarbital and phenobarbital in saliva. The barbiturate is extracted with chloroform, alkylated with bis(2-chloroethyl) sulphate, and quantified using a non-polar (SE-30) column and electron-capture detection. The procedure has been applied to the determination of the salivary half-lives of amobarbital and, for the first time, pentobarbital following administration of the drugs to human volunteers. The scale and sensitivity of detection are suitable for use in forensic or other medico-legal work.

The effect of diazepam, chlorpromazine and amobarbital on the contingent negative variation

The effects of diazepam (5 mg), chlorpromazine (CPZ, 12.5 mg) and amobarbital (100 mg) on the contingent negative variation (CNV) at Cz and Oz were studied in groups of 10 subjects each. Amobarbital and placebo were given by the double-blind crossover method. Two kinds of experimental paradigms were used: Click (warning stimulus, S1)--flashes (imperative stimulus, S2)--and click--electrical stimulation--motor response. The results obtained were as follows; 1) CNV amplitudes were decreased significantly by administration of diazepam only at Cz when S2 was flashes and at both Cz and Oz when S2 was electrical stimulation. 2) CPZ-induced effects were of either augmentation or decrement in CNV amplitudes depending on the subject and on the modality of S2. Involvement of dose-dependent factor was suggested. 3) Amobarbital and placebo did not give any significant changes to the CNV. 4) Significant correlations between CNV amplitudes at Cz and Oz were found before drug administration and even after taking drugs exclusive of diazepam. Its decremental ratio from Cz to Oz was approximately 0.6 to 0.8. The correlation coefficient became to be insignificant after taking diazepam only when S2 was flashes.

Plasma pentobarbitone levels. Influence of the preparation, route and method of administration

In fit women plasma pentobarbitone was measured by gas-liquid chromatography after 100 mg given by mouth or intramuscular injection in the buttock using aqueous and organic solutions. Differences in plasma levels with the two solutions were not striking. Considerable inter-administrator difference occurred with significantly higher plasma levels when the drug was injected by a doctor using a 4 cm 21 s.w.g. needle as compared with nurses who used no specified injection technique. The oral route gave significantly higher plasma levels than nurse-given injections.

Pharmacokinetics and relative bioavailability of heptabarbital and heptabarbital sodium after oral administration to man

A method has been developed for the quantitative determination of heptabarbital [5-(1-cyclohepten-1-yl)-5-ethylbarbituric acid] in human plasma after administration of single therapeutic doses of the drug. It involves a single extraction step followed by gas chromatography with alkali flame ionization detection, and the results were linear in the concentration range 0.125 - 5.0 mug/ml plasma. The pharmacokinetics and relative bioavailability of heptabarbital and heptabarbital sodium were studied in a crossover design in 7 healthy volunteers after oral administration of 20 tablets containing 200 mg heptabarbital and hard gelatine capsules containing an equivalent amount of its sodium salt. Heptabarbital concentrations in plasma were determined at regular intervals. The absorption of heptabarbital from the tablets absorbed more rapidly and peak concentrations occurred between 1/3 and 2 h. In all cases the elimination of heptabarbital could be described by a single first-order process with an average half-life of 7.6 h (range 6.1 - 11.2 h). The half-life of the drug in each individual was about the same in the two trials. The relative bioavailability in each volunteer was estimated by comparing the areas under the plasma concentration curves. The sodium salt had an average bioavailability of 83% relative to the free acid. In some volunteers urinary excretion of unchanged heptabarbital was measured; cumulative excretion amounted to 0.16 - 0.30% of the administered dose. Four volunteers received one tablet each night for eight or ten days, but no accumulation was found. In three volunteers the half-life of the drug prior to and after these experiments did not change, whereas in the other volunteer the half-life decreased from 7.1 to 4.6 h. The possibility of enzyme induction should be considered when heptabarbital is taken regularly. It was concluded that heptabarbital was a suitable drug for the treatment of insomnia, since its half-life was rather short. Heptabarbital sodium may be used for induction of sleep, whereas Medomin tablets, i.e. heptabarbital free acid, may be prescribed when the maintenance of sleep is the primary reason for treatment with a hypnotic drug.

Pharmocokinetics of hexobarbital in man after intravenous infusion

The plasma levels of hexobarbital in humans were determined during and after a 30-min or 60-min zero-order intravenous infusion. Hexobarbital kinetics could be described by conceiving the body to exhibit two compartments. The plasma concentrations were fitted to the postinfusion equation and the parameters intrinsic to the two-compartment open model were estimated. The elimination half-life varied considerably among the 14 individuals (160-441-min), which could mainly be explained by the greatly varying metabolic clearance of the compound (123-360 ml/min). The apparent volume of distribution per kilogram of body weight was relatively constant (1.10 plus or minus 0.12 liters/kg).

Blood barbiturate levels in a patient dependent upon amylobarbitone sodium

In a barbiturate dependent patient, the blood barbiturate was less than 0·2 mg% two and a half hours after an oral dose of 200 mg amylobarbitone sodium. Amylobarbitone was withdrawn, and the patient was maintained on phenobarbitone, with a blood barbiturate level that remained at about 4·0 mg% over several weeks. Themost likelyexplanation of the findings is that the oxidation of amylobarbitone, but not phenobarbitone, is accelerated in patients dependent on the former drug.