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The pharmacokinetic effect of a single oral in dose of 20 mg clobazam was studied in 15 patients with liver disease and in 6 healthy volunteers. Plasma concentrations of clobazam and its main metabolite, norclobazam, were measured by gas liquid chromatography. Clobazam was rapidly absorbed. Peak plasma concentrations were 350 +/- 63 ng/ml at 1.7 +/- 0.8 hr in healthy volunteers, 239 +/- 70 ng/ml at 3 +/- 1.9 hr in patients with viral hepatitis and 240 +/- 113 ng/ml at 2.5 +/- 1.5 hr in patients with cirrhosis. Total distribution volume was 173 +/- 88 l and 168 +/- 71 l in patients with viral hepatitis and cirrhosis respectively, and 81 +/- 20 l in volunteers. Corresponding half-life values were 47 +/- 18 hr and 51 +/- 21 hr in patients and 22 +/- 6.3 hr in volunteers. The difference between patients was not significant, whereas the difference between patients and volunteers was significant.

The authors monitored the plasma levels of clobazam (CLO) and its principal metabolite, N-desmethylclobazam (NCLO) during chronic treatment of more than 400 epileptic patients receiving different co-medications, such as phenytoin (PH), carbamazepine (CBZ), sodium valproate (VPA) and phenobarbital (PB). This study investigated the influence of age and antiepileptic drugs on plasma levels of CLO and NCLO. Plasma concentrations measured 3 hr after morning administration of CLO varied from 30 to 700 [formula; see text] for CLO, and from 160 to 7000 [formula; see text] for NCLO. Plasma levels of CLO were higher in patients aged 20-30 years. NCLO concentrations increased with age up to 20 years. Coadministered antiepileptic compounds significantly decreased maximal plasma levels of CLO. Moreover, PH and CBZ a significantly increased the plasma levels of NCLO. Results on the influence of CBZ on CLO kinetics were confirmed in a group of ten patients receiving PB and VPA and later PB, VPA and CBZ as CLO associated drugs. The influence of VPA on the pharmacokinetics parameters of CLO was also evaluated in a patient in the latter group.

A simultaneous consideration of plasma and urine data of unchanged drug and active metabolites, taking into account the metabolic process of the precursor, is described. The maximum likelihood principle was used to estimate parameters. This methodology is highly efficient in determining the contribution of the two main and active metabolites in the pharmacological response of ethyl loflazepate. It also may serve in the search for optimum dosage regimens in clinical practice.

The pharmacokinetics of tetrazepam (Myolastan, Musaril), were studied in 12 healthy volunteers. Tetrazepam was given orally as a single dose of 50 mg and repeated administration for 5 consecutive days of 50 mg at 12-h intervals, in tablet form. Tetrazepam was measured in plasma using a selective and sensitive GLC method. Tetrazepam is rapidly absorbed after oral administration with a peak plasma level of 0.49 +/- 0.10 mg/l at 0.94 +/- 0.47 h. The drug is widely distributed in the organism with an apparent volume of distribution of 6.7 +/- 2.1 l/kg. Tetrazepam is eliminated with a half-life of 22 +/- 4 h and can be classified as a benzodiazepine with medium half-life value. This medium half-life is the result of the high hepatic clearance of the drug in spite of its large distribution volume. Since in this study 6 male and 6 female volunteers were studied it was possible to compare the pharmacokinetic profile in the two groups. No significant differences were observed. No differences were observed between the pharmacokinetic values after a single dose or after repeated administration.

A method has been developed for gas-chromatographic determination of clonazepam ("Rivotril" or "Ro 5-4023") in plasma, using methyl-clonazepam ("Ro 4082") as an internal standard. Following extraction of the benzodiazepines and hydrolysis, the benzophenones are analyzed by gas-chromatography, using a glass column filled with 3% OV 225 on Gas Chrom Q and a 63Ni electron-capture detector. The technique has good selectivity. The limit of sensitivity is less than 1 ng/ml of plasma. Using this method the plasma kinetics of clonazepam may be studied in man and the correlations between plasma levels and therapeutic activity investigated. It is also available for toxicological analysis, as well as pharmacovigilance purpose. The same internal standard and a similar method can also be used for the determination of flunitrazpem ("Rohypnol" or "Ro 5-4200") and its major metabolite (N-desmethyl-flunitrazepam) in plasma.

A gas chromatographic assay with electron-capture detection (GC--EC) is described for the metabolites of ethyl loflazepate (Victan), a new benzodiazepine with a potent anti-anxiety activity, in biological fluids. Since the parent drug undergoes a first-pass effect, pharmacokinetic data may only be obtained by measuring the total levels of two of the major metabolites. Accurate data can not be obtained for the metabolites separately since one of them (M1) is chemically transformed to the other (M2) during plasma sampling, storage and extraction. A sensitive, specific and accurate GC--EC assay is developed using a synthetic analogue of M2 as an internal standard. The limit of detection in plasma is approximately 2 ng/ml and the precision about 3% (within-run and between-run). The method is applied to plasma samples collected after oral administration of 2 mg and 4 mg of the drug in tablet form to human volunteers. The results obtained are correlated with those from an existing gas chromatographic--mass spectrometric assay. A very good correlation between the results (inter-laboratory comparison) is obtained, validating both techniques.

Owing to the pharmacological and clinical importance of the determination of plasma and urine levels of the hydroxy metabolites of clobazam and N-desmethylclobazam in healthy volunteers and in epileptic patients, a high-performance liquid chromatographic (HPLC) method was developed that permits the determination of all these compounds in the same plasma or urine sample. The method involved ether extraction at pH 13 with diazepam as internal standard for the measurement of clobazam and N-desmethylcobazam, followed by ether extraction at pH 9 with nitrazepam as internal standard for the measurement of the hydroxy derivatives. The limit of detection was about 10-20 ng/ml for each of these compounds. Applications to patients were limited by chromatographic interferences between the hydroxy metabolites and some medications currently associated with clobazam in the treatment of epilepsy. The only interference in clobazam and N-desmethylclobazam analysis was from N-desmethyldiazepam. Despite these inconveniences, this HPLC procedure appears to be the only available method for the simultaneous quantification of clobazam and its three main metabolites.

The kinetics of ethyl loflazepate were studied in patients with various degrees of renal failure. A strong correlation was noted between urinary excretion of metabolite loflazepate and creatinine clearance. In contrast, elimination half-life and total plasma clearance of the sum of loflazepate + descarboxyloflazepate seemed to be independent of the degree of renal impairment. These results indicate the absence of a risk of accumulation of the 2 main and active metabolites of ethyl loflazepate in patients with renal failure.

The pharmacokinetic behavior of clobazam and its main metabolite, norclobazam, was investigated in healthy subjects after single dose administration, repeated dose administration (28 days) and discontinuation of the treatment (15-day follow-up). The aim of the study was to confirm the time-invariance of the clobazam and/or norclobazam kinetics, in order to evaluate the predictive value of the single dose parameters for chronic administration of this drug. The comparisons of parameters after single dose and for 15 days following cessation of chronic administration, experimental and simulated plasma level-time courses, experimental and calculated steady-state minimum plasma concentrations, and half-life values at apparent and deep elimination phase, indicate a time-invariant behavior of clobazam, whereas the norclobazam pharmacokinetics appeared to be clearly time-dependent. The clinical importance of this difference cannot be adequately assessed until more is known about the contribution of norclobazam to the overall effect of the parent drug.

A capillary gas-liquid chromatographic method for the determination of 3-methylclonazepam in plasma was developed. This method involved a single extraction by butyl acetate followed by analysis of the organic extract on a CP-Sil 5 glass capillary column with detection by electron capture. The detection limit was about 0.1 ng/ml, and the inter- and intra-assay precision did not exceed 8% for the concentration range 0.1-6.0 ng/ml. Specificity towards some of the possible metabolites in human plasma was demonstrated. This method was used for the measurement of the pharmacokinetic parameters of 3-methylclonazepam in healthy volunteers after a single intravenous administration of 1 mg, and oral administrations of 1 and 4 mg.

The authors have developed a gas chromatographic method for the simultaneous quantification of quazepam in plasma and its two main metabolites, 2-oxoquazepam and N-desmethylquazepam. This method involves an extraction from plasma using butyl acetate, and an analysis by electron-capture detection on a CP-Sil 5 WSCOT capillary column. Intra- and inter-day precision and accuracy were better than 10% for each of these three compounds, even near their detection limit estimated at 0.2 ng/ml. Linearity proved satisfactory between 0.2 and 60-70 ng/ml. For endogenous plasma components, adequate specificity was achieved. Despite some inconveniences, a long analysis time, a progressive saturation of the column owing to a low oven temperature, and a relatively short life-span of the CP-Sil 5 columns, this method was the only one available in the literature for the quantification of quazepam and its metabolites from the same plasma sample. It was successfully applied to phase I studies in healthy volunteers.

A method is developed for gas-chromatographic determination of flunitrazepam, desmethylflunitrazepam and clonazepam in plasma, using methylclonazepam as internal standard. Following extraction of the benzodiazepines and their hydrolysis, the benzophenones are analyzed by gas-chromatography, with a glass column filled with 3% OV-225 on Gas Chrom Q and a 63Ni electron capture detector. The technique has a good selectivity. Its limit of sensitivity is about 0.5 ng/ml of plasma. It is suitable for investigations on pharmacokinetics and bioavailability as well as for monitoring the correlation between plasma level and therapeutic efficacy and toxicology.

The disposition of ethyl loflazepate (Victan) was studied on 12 healthy male volunteers after administration of the two oral formulations of the drug: one 4-mg tablet and two 2-mg tablets according to an open crossover single dose comparison. A model-independent analysis and a model-dependent approach were used to treat experimental data. Appropriate statistical tests (ANOVA, Wilcoxon test, Westlake test for model-independent parameters; principal components analysis, Hotelling T2 test for model-dependent parameters) demonstrated the bioequivalence of the two formulations.

A method is developed for direct gas-chromatographic determination of clonazepam (Rivotril) and its main metabolite, 7-amino clonazepam, in plasma, using desmethylflunitrazepam as internal standard. Following selective extraction, the benzodiazepines are analyzed by gas-chromatography, with a glass column filled with 3% OV17 on Gas Chrom Q and 63Ni electron capture detector. The procedure, which requires neither hydrolysis nor derivatisation, has a good selectivity. The sensitivity is 5 ng/ml of plasma for a valid quantitative determination. We have to improve this limit for fine pharmacokinetic studies, but the method is already available for therapeutic and pharmacovigilance controls. It is also suitable for diagnostic of eventual overdosing or poisoning, based on plasma or urine analysis.