Inhibitors of alprazolam metabolism in vitro: effect of serotonin-reuptake-inhibitor antidepressants, ketoconazole and quinidine.
1. The biotransformation of the triazolobenzodiazepine alprazolam (ALP) to its hydroxylated metabolites (4-OH-ALP and alpha-OH-ALP) was evaluated in human, monkey, rat, and mouse liver microsomes. 2. In all species 4-OH-ALP was the principal metabolite, accounting for 84% of clearance in human microsomes compared with 16% for alpha-OH-ALP. 3. Among the serotonin-specific reuptake inhibitors fluoxetine (FLU) and sertraline (SERT), and their respective demethylated metabolites norfluoxetine (NOR) and desmethylsertraline (DES), NOR was the most potent inhibitor (mean Ki for 4-OH-ALP formation in humans: 11 microM), FLU the weakest (Ki = 83 microM), with SERT and DES falling in between (Ki = 24 and 20 microM). 4. The in vitro data predict 29% inhibition of ALP clearance at mean FLU and NOR plasma concentrations of 77 ng ml-1 and 72 ng ml-1, respectively, after correction for liver:water partition ratios in the range of 12-14. The observed mean degree of inhibition in a previous in vivo study was 21%. 5. Ketoconazole was a potent inhibitor of ALP metabolism in vitro (Ki = 0.046 microM), suggesting that ALP hydroxylation is mediated by the cytochrome P450-3A sub-family. Quinidine was a weak inhibitor (Ki = 626 microM).
von Moltke
L L
LL
Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA 02111.
Greenblatt
D J
DJ
Cotreau-Bibbo
M M
MM
Harmatz
J S
JS
Shader
R I
RI
D000328:Adult; D000368:Aged; D000525:Alprazolam / Q000378:metabolism* / Q000493:pharmacokinetics; D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology*; D001711:Biotransformation; D005260:Female; D006801:Humans; D006900:Hydroxylation; D007654:Ketoconazole / Q000494:pharmacology*; D008252:Macaca fascicularis; D008297:Male; D051379:Mice; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D008875:Middle Aged; D011802:Quinidine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D013045:Species Specificity
D000525:Alprazolam; D000928:Antidepressive Agents; D007654:Ketoconazole; D011802:Quinidine; D017367:Selective Serotonin Reuptake Inhibitors