New chiral high-performance liquid chromatographic methodology used for the pharmacokinetic evaluation of dexfenfluramine.

A new chiral high-performance liquid chromatographic (HPLC) method utilizing ultraviolet (UV) detection has been developed for determining plasma and urinary concentrations of d-fenfluramine and its major metabolite d-norfenfluramine, while being able to determine the possible presence of l-fenfluramine after oral administration of enantiopure d-fenfluramine hydrochloride. Sensitivity, stability, and specificity were enhanced by derivatizing the extracted analytes with 3,5-dinitrophenylisocyanate while utilizing a Pirkle-type chiral recognition approach. In vitro and in vivo statistical data are analogous. Overall plasma inter-assay precision was less than 7% with a minimum quantitation limit of 10 ng/ml. Overall urine inter-assay precision was also less than 7% with a minimum quantitation limit of 25 ng/ml.

Determination of dexfenfluramine and nordexfenfluramine in urine by high-performance liquid chromatography using ultraviolet detection.

A method to determine the concentration of dexfenfluramine and its active metabolite nordexfenfluramine in human urine from healthy volunteers is described utilising a high-performance liquid chromatographic procedure with liquid-liquid extraction and ultraviolet detection. Analytes are measured after extraction of alkalinised urine with diethyl ether and subsequent back extraction with 0.5 M H2SO4 and with chromatography performed on a reversed-phase C18 column, using a mobile phase of acetonitrile-50 mM K2HPO4 (25:75, v/v) (flow-rate 1.3 ml/min) and ultraviolet detection at 210 nm. The sensitivity of the technique (10 ng/ml) is appropriate to measure both parent drug and metabolite in urine in humans for up to 5 days after a single 30-mg dose. The method is selective, reproducible (within- and between-day coefficient of variation ranged from 4.2 to 15%) and accurate (bias less than 8%) and thus suitable for dexfenfluramine pharmacokinetic investigations.

The measurement of d-fenfluramine and its metabolite, d-norfenfluramine in plasma and urine with an application of the method to pharmacokinetic studies.

1. A specific and sensitive gas chromatographic assay is described for the measurement of d-fenfluramine and its de-ethylated metabolite, d-norfenfluramine, in biological fluids, together with some data on its application to the oral pharmacokinetics of the drug. 2. The analytical method developed has advantages over the previously described methods since it uses nitrogen specific detection and, when applied routinely, enables smaller sample volumes to be used (typically 1 ml of plasma) with a shorter chromatography time and an improved sensitivity (minimum quantifiable level of 2.5 ng ml-1). 3. Peak plasma concentrations of 22 and 24 ng ml-1 of intact drug were reached at 4 h after an oral dose of 14C-d-fenfluramine hydrochloride (30 mg) given to two volunteers as part of a metabolism and disposition study. Subsequently, concentrations of intact drug declined monoexponentially with a half-life of approximately 13 h. Peak concentrations of 10 and 8 ng ml-1 of the metabolite, d-norfenfluramine, were reached after 4 and 6 h and were maintained as a plateau for a further 4-6 h. Assessment of the half-life of the metabolite could not be made because of lack of data on the terminal portion of the curves. 4. The urinary excretion of d-fenfluramine (6.0 and 10.6% of the dose) and d-norfenfluramine (5.8 and 8.8% of the dose) was low, indicating extensive metabolism of the parent drug.

The effect of fenfluramine on weight loss during restricted dietary regimes.

Fenfluramine therapy 180 mg per day did not increase the rate of weight loss in obese patients either undergoing therapeutic starvation or receiving a 300 kcal diet; neither did the drug alter those biochemical changes associated with these dietary regimes. These results suggest that fenfluramine does not cause weight loss in the obese patient by a major metabolic action but by its effect on appetite. However, there were significant differences in the ratios of fenfluramine to norfenfluramine in the plasma and urine of patients on each dietary regimen.