Determination of S 12024 enantiomers in human plasma by liquid chromatography after chiral pre-column derivatization.

S 12024-2 is a new drug in phase II development that possesses cognitive enhancing properties. As its molecular structure has a chiral centre, a stereoselective method for the analysis of both enantiomers in human plasma has been developed. The method involves pre-column derivatization of the amine moiety with a homochiral reagent (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC), and chromatographic separation of the two diastereoisomers on an achiral reversed-phase cyanopropyl column, with fluorimetric detection (lambda ex = 260 nm; lambda em = 310 nm). A liquid-liquid extraction procedure with diethyl ether-dichloromethane (70:30, v/v) was used for sample preparation. This technique provides a linear response for both enantiomers over a concentration range of 10-500 ng ml-1 and the quantitation limit was set at 5 ng ml-1 in human plasma. Within-day and between-day precision and accuracy are within 9% limits for all concentrations assessed. This procedure was therefore used for determining both enantiomers in human plasma following oral administration of racemic S 12024-2 to elderly healthy subjects.

Human pharmacokinetics of a new Vinca alkaloid S 12363 with use of a monoclonal antibody-based radio- or enzyme immunoassay.

S 12363 is a new Vinca alkaloid derivative, characterized by the grafting of an alpha-aminophosphonate, onto the Vinca nucleus, facilitating drug penetration and increasing intracellular drug retention. As a high cytotoxic activity had been demonstrated in in vitro and in vivo models recommended by the National Cancer Institute, a phase I trial was initiated in cancer patients. In order to quantify S 12363 systemic levels in humans, two monoclonal antibody-based immunoassays, RIA (radio-) and EIA (enzyme immunoassay) were developed. The gamma-emitting probe used in the RIA, 125I-(deacetyl-O4-vinblastine)-tyramine, bound very tightly to the monoclonal antibody (dissociation constant, Kd = 2.5 x 10(-11) M), demonstrating a high affinity mainly directed toward the catharantine nucleus (vindesine, vincristine, vinblastine, 100% cross-reactivity; vinorelbine, 0.3% cross-reactivity). In the EIA, a deacetyl O4-vinblastine/ovalbumine conjugate was used as the competing antigen. Its binding to the monoclonal antibody was revealed by an anti-mouse immunoglobulin G conjugated to biotin which interacts with streptavidin labeled with alkaline phosphatase. This method permitted obtaining nearly the same sensitivity and reproducibility with EIA as with RIA, their respective minimum quantitation limits being 0.100 and 0.040 ng/ml (106 and 42 pM) of S 12363 in plasma. These assays allowed the study of S 12363 systemic pharmacokinetics in cancer patients during a phase I trial up to 72 h after dosing. As determined by RIA, the S 12363 plasma profile was triphasic with a terminal half-life; t1/2 gamma = 49 +/- 16 h, a plasma clearance, CL = 0.14 +/- 0.04 liter/h/kg, and a volume of distribution at steady state, Vdss = 5.0 +/- 2.8 liter/kg. The pharmacokinetics of S 12363 is linearly related to dose when increased from 0.08 up to 0.84 mg/m2 in humans. Its plasma profile and pharmacokinetic parameters are close to those of other Vinca alkaloids with clearance and terminal half-life being intermediate between those of vinblastine and vincristine. Therapeutic doses are 4 to 10 times lower and should be a direct consequence of the higher uptake and retention by the cells of this new aminophosphonate Vinca alkaloid derivative.

Radioimmunoassays for a new angiotensin-converting enzyme inhibitor, zabicipril, and its active metabolite, zabiciprilat, in human plasma.

Zabicipril (Z), a new angiotensin-converting-enzyme inhibitor under development, is a prodrug that has to be deesterified in vivo to the active metabolite, zabiciprilat (ZT), to reach its antihypertensive pharmacological properties. Two radioimmunoassays have been developed for the measurement of both Z and ZT in human plasma. Anti-Z and anti-ZT antibodies were raised in rabbits against their respective lysine analogues conjugated to bovine serum albumin. [3H]Z and [3H]ZT were used as radioligands for the prodrug (Z) and the drug (ZT), respectively. Studies on anti-Z antiserum specificity showed no significant cross-reactivity (< 0.1%) with the active metabolite (ZT); similarly, Z is poorly recognized (0.5%) by the anti-ZT antiserum. Both antisera showed little cross-reaction (2%) with glucuronide metabolites. The sensitivities of the assays were 1 and 0.2 ng/mL for Z and ZT, respectively. Interassay coefficients of variation ranged from 9 to 12% for Z at 2-50 ng/mL and from 8 to 13% for ZT at 0.5-5 ng/mL. These assays were used to investigate the pharmacokinetic profile of both Z and its pharmacologically active metabolite ZT after intravenous infusion of Z in human volunteers.

Influence of acetaminophen on antipyrine kinetics in rats.

Studies have suggested that acetaminophen may inhibit the liver metabolism of several drugs. Due to the expected clinical relevance of these findings, the present study was undertaken to examine acetaminophen effects on in vivo drug metabolism in the rat, using the model substrate antipyrine. Oral doses of 15 mg/kg acetaminophen were administered twice daily for 7 days. Antipyrine kinetics were determined before and immediately after acetaminophen treatment in rats (used as their own control). Acetaminophen treatment significantly increased antipyrine half-life by 29% and reduced its clearance by 24%, without affecting its volume of distribution. Further studies are warranted to determine the relevance and mechanism of these findings.

The determination of fenspiride in human plasma and urine by liquid chromatography with electrochemical or ultraviolet detection.

A selective and sensitive method for the determination of fenspiride in biological fluids is described. The method involves liquid-liquid extraction followed by separation on a reversed-phase column with electrochemical detection for low levels of the drug in plasma (less than or equal to 100 ng ml-1) or UV absorption for higher concentrations in plasma or urine. The method is suitable for pharmacokinetic analyses and drug monitoring studies.