Metabolism of actisomide in the dog, monkey and man: a novel rearrangement of N-dealkylated metabolites

A global examination of allometric scaling for predicting human drug clearance and the prediction of large vertical allometry**This work was presented at the American Association of Pharmaceutical Scientists Annual meeting, Salt Lake City, USA, Oct. 26, 2003

Allometrically scaled data sets (138 compounds) used for predicting human clearance were obtained from the literature. Our analyses of these data have led to four observations. (1) The current data do not provide strong evidence that systemic clearance (CL(s); n = 102) is more predictable than apparent oral clearance (CL(po); n = 24), but caution needs to be applied because of potential CL(po) prediction error caused by differences in bioavailability across species. (2) CL(s) of proteins (n = 10) can be more accurately predicted than that of non-protein chemicals (n = 102). (3) CL(s) is more predictable for compounds eliminated by renal or biliary excretion (n = 33) than by metabolism (n = 57). (4) CL(s) predictability for hepatically eliminated compounds followed the order: high CL (n = 11) > intermediate CL (n = 17) > low CL (n = 29). All examples of large vertical allometry (% error of prediction greater than 1000%) occurred only when predicting human CL(s) of drugs having very low CL(s). A qualitative analysis revealed the application of two potential rules for predicting the occurrence of large vertical allometry: (1) ratio of unbound fraction of drug in plasma (f(u)) between rats and humans greater than 5; (2) C logP greater than 2. Metabolic elimination could also serve as an additional indicator for expecting large vertical allometry.

Metabolism of a novel antiarrhythmic agent, bidisomide, in man: use of high resolution mass spectrometry to distinguish desisopropyl bidisomide from desacetyl bidisomide

1. Metabolism of bidisomide, a novel antiarrhythmic agent, was studied in man, and was not extensive as evidenced by the fact that approximately 60 and 70% of the radioactive doses were recovered as the parent drug after i.v. and oral administration respectively. 2. The mass spectra of bidisomide metabolites indicate that the two major metabolic pathways of bidisomide were hydroxylation of the piperidine ring and N-dealkylation. The latter occurred on the side chain containing the piperidine ring or the isopropyl group. The N-dealkylated metabolite on the side chain containing the piperidine ring was cyclized to result in a pyrrolidone metabolite. 3. The N-dealkylated metabolite, desisopropyl bidisomide, was identified by comparing its high resolution mass spectrum to that of authentic desacetyl bidisomide. 4. In the hydroxylation pathway, both mono- and dihydroxylated metabolites of the piperidine ring were observed. The exact location of the hydroxyl groups on the piperidine ring was not determined.