Pharmacokinetic studies of (-)-deprenyl and some of its metabolites in mouse

(-)-Deprenyl is a selective irreversible inhibitor of MAO-B. The parent compound is responsible for the enzyme inhibitory effect, but its metabolites are also playing a role in the complex pharmacological activity of the substance. In the present studies male NMRI mice were treated orally, subcutaneously, intraperitoneally and intravenously with 5 mg/kg of (-)-deprenyl. The time related changes of the plasma concentrations of the parent compound and its main metabolites (methamphetamine, desmethyl-deprenyl and amphetamine) were determined by GC/ MSD technique. The main pharmacokinetic parameters (C(max), t(max), t1/2beta, AUC(0-6), AUC(0-infinity)) have been calculated. (-)-Deprenyl is well absorbed after oral and parental treatment. The peak concentrations (C(max)) were reached at 15 min after treatment and the absorption was followed by a fast elimination (t1/2beta < or = 2h). (-)-Deprenyl has an intensive "first pass" metabolism after oral treatment; only 25% of the parent compound reaches the systemic circulation. Increased bioavailability was detected after subcutaneous (87.1%) and intraperitoneal (78.7%) administration. The main metabolic pathway of (-)-deprenyl is the N-depropargylation, leading to the formation of methamphetamine. N-demethylation of (-)-deprenyl leads to formation of desmethyl-deprenyl. Amphetamine is produced from both former metabolites. After oral treatment the plasma concentrations of methamphetamine are higher during the first 6 h than that of (-)-deprenyl, while the opposite was found after parental treatment. The results indicate, that (-)-deprenyl, a potent MAO-B inhibitor, might induce a different spectrum of activity (e.g. antidepressant), when it is administered parenterally (transdermally). The new spectrum can be due to the special pharmacokinetic behaviour of the inhibitor.

Transdermal formulations of deprenyl: guinea pig and pig models

The efficacy of many drugs relies on their presence at the site of action over a period of time. The retardation or programmed release capability of the conventional dosage forms like oral and parenteral are limited and toxic and undesired side-effects may occur after their applications. These problems may be solved using transdermal delivery systems. Transdermal systems are aimed for local, or systemic action. In the letter case controlling the rate of delivery or modulating the distribution in the organism. The selection of an adequate biological method of evaluating a new transdermal formulation is a critical point of the development. The in vitro methods can help in the characterization of the different formulas, but without an in vivo disposition study they cannot give relevant information about the expectable therapeutic behavior. We adapted and improved an in vivo test system for the evaluation of new transdermal particulate systems (patches) and liposomes containing deprenyl selegiline as active ingredient. The in vivo evaluation system consists of two steps: 1. Full biodisposition study on guinea pig, using isotope labeled selegiline. 2. Biodisposition studies on domestic pigs including dose, area, surface dependence and comparative bioavailability with traditional dosage forms and application moods. Specific examples of these studies and experimental technology are presented.

Gas-chromatographic study on the stereoselectivity of deprenyl metabolism

The metabolism and urinary elimination of both (-)-deprenyl and (+)-deprenyl have been studied. Gas-chromatographic analysis with mass specific detection indicated that the metabolism of (-)-deprenyl results in a large excess of methamphetamine compared to amphetamine, while the metabolism of (+)-deprenyl gave nearly equal amounts of amphetamine and methamphetamine. A novel deprenyl metabolite, phenylacetone, was also identified in our studies.