ABSORPTION AND PRESYSTEMIC METABOLISM OF NEFAZODONE ADMINISTERED AT DIFFERENT REGIONS IN THE GASTROINTESTINAL-TRACT OF HUMANS

Purpose. The absorption and disposition of nefazodone (NEF) and its metabolites hydroxynefazodone (HO-NEF), m-chlorophenylpiperazine (mCPP) and triazole dione (dione) were assessed in 10 healthy subjects following infusion of NEF solution into the proximal and distal regions of the intestine vs administration of NEF solution orally by mouth. Methods. NEF HCl (400 mg) was infused over 5 hours into the proximal or distal intestine through a nasogastric tube, or orally ingested in 10 divided doses over 4.5 hours. The three treatments in the three-period crossover design were separated by one week. Results. The bioavailability of NEF, based on AUC(INF), from proximal and distal regions relative to that from oral administration was 97% and 106%, respectively. NEF was absorbed equally well from all three treatments with median Tmax of 5.0 hours which coincided with the duration of infusion. Mean Cmax of NEF was not different between proximal and oral administrations, however, mean Cmax after distal instillation was 40% lower than that after oral administration. Exposure to HO-NEF, mCPP and dione, following proximal instillation was also comparable to that after oral administration. AUC(INF) of HO-NEF and dione was significantly lower after distal instillation compared to that after oral administration but AUC(INF) of mCPP was not. Cmax of all metabolites was significantly lower after distal administration in comparison to oral treatment. Terminal half-life for NEF, HO-NEF and mCPP after distal administration was longer than the other two treatments. Conclusions. NEF is absorbed throughout the length of the gastrointestinal tract which supports the development of an extended-release formulation of NEE The exposure to the metabolites (relative to NEF) was lower from the distal intestinal site compared to the proximal and oral site which may be explained by a reduced first pass of NEF by the cytochrome P450 3A4 in the distal intestine.