Mass spectrometric identification of amiodarone N-monodesethyl metabolite and application of an HPLC method to a pharmacokinetic study.

Identification of an amiodarone metabolite in the plasma of patients receiving a single dose of the drug was carried out by mass-spectrometry following extraction and HPLC separation. The kinetics of the plasma concentrations of unchanged compound and its identified metabolite (N-monodesthyl-amiodarone) were studied in six patients after a single administration of amiodarone by oral or intravenous routes, using a sensitive and specific high-performance liquid chromatographic method. The observed plasma clearance rate for the drug varied from 0.2 to 0.5 1.h-1.kg-1 of body weight; and the elimination half-life of the unchanged compound was found to be approximately 21 hours. Oral bioavailability, as determined in one patient, was about 60%. The proportion of the metabolite found in the plasma following a single oral administration was significantly higher than that observed after infusion. The ratio of areas under the curves for metabolite-to-unchanged compound was 0.55 and 0.13 for oral and intravenous doses respectively. During a circumscribed study carried out in five patients receiving oral doses of the drug (daily dose varied from 2.6 to 9.3 mg/kg) accumulation of the metabolite was observed. The mean of the plasma level ratios (metabolite to-unaltered drug) obtained in five patients was approximately 0.97.

Pharmacokinetics of metapramine (19560 RP) in man after infusion and intravenous injection.

The time course of the plasma level metapramine following infusion at three different rates (1.18, 2.36 and 4.71 mg/h) has been studied in six healthy volunteers. The correlation coefficient of drug concentration and rate of infusion was 0.974 (alpha less than 0.001, n = 18). Plasma clearance, estimated from the steady-state level, varied from 68 to 1071/h. 3 subjects also received 35 mg of drug by i.v. bolus injection and plasma concentrations were determined at set times for up to 24 h. The plasma level of metapramine decreased tri-exponentially, with a terminal half-life of about 7.4 h. The plasma clearance after i.v. injection was in good agreement with that observed during the infusion study. Apparent volumes of distribution ranged from 41.9 to 90.31.

Determination of 7-amino-flunitrazepam (Ro 20-1815) and 7-amino-desmethylflunitrazepam (Ro 5-4650) in plasma by high-performance liquid chromatography and fluorescence detection.

A high-performance liquid chromatographic method for the simultaneous determination of 7-amino-flunitrazepam (Ro 20-1815) and 7-amino-desmethylflunitrazepam (Ro 5-4650) in plasma is described. After extraction with an organic solvent, the compounds and their internal standard (7-amino-methylclonazepam or Ro 5-3384) are derivatized with fluorescamine and chromatographed on a reversed-phase muBondapak C18 column using pH 8 buffer solution-acetonitrile (3:1) as mobile phase. The detection is performed by a fluorometer at excitation and emission wavelengths of 390 and 470 nm, respectively. The sensitivity limit is about 1 ng/ml of plasma for both 7-amino-flunitrazepam and 7-amino-desmethylflunitrazepam. The method has been applied to the determination of plasma levels of these substances during pharmacokinetic studies of flunitrazepam, desmethylflunitrazepam and 7-amino-flunitrazepam.

Highly specific and sensitive method for the determination of flunitrazepam in plasma by electron capture gas-liquid chromatography.

A sensitive and highly specific electron capture gas-liquid chromatographic method was developed for the determination of flunitrazepam in human plasma. The method involves selective extraction of the drug into hexane from plasma at pH 9 followed by back-extraction into 2 N sulfuric acid for clean-up procedure, and re-extraction by 20% toluene-hexane at pH 2. The sensitivity limit of the method is 0.5 ng/ml of plasma. Its specificity was tested for about 45 drugs frequently administered as co-medication in hospitalized patients, including other benzodiazepines. The method proves very suitable for investigating the clinical pharmacokinetics of flunitrazepam as well as for monitoring therapeutic plasma levels and in forensic situations following over-dosage, and was successfully applied within a clinical pharmacokinetic study in an intensive care unit.

Analysis of the metabolites of ethyl loflazepate by gas chromatography with electron-capture detection.

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.