In vitro, pharmacokinetic, and pharmacodynamic interactions of ketoconazole and midazolam in the rat.
Interactions of midazolam and ketoconazole were studied in vivo and in vitro in rats. Ketoconazole (total dose of 15 mg/kg intraperitoneally) reduced clearance of intravenous midazolam (5 mg/kg) from 79 to 55 ml/min/kg (p < 0.05) and clearance of intragastric midazolam (15 mg/kg) from 1051 to 237 ml/min/kg (p < 0.05), increasing absolute bioavailability from 0.11 to 0.36 (p < 0.05). Presystemic extraction occurred mainly across the liver as opposed to the gastrointestinal tract mucosa. Midazolam increased electroencephalographic (EEG) amplitude in the beta-frequency range. Ketoconazole shifted the concentration-EEG effect relationship rightward (increase in EC(50)), probably because ketoconazole is a neutral benzodiazepine receptor ligand. Ketoconazole competitively inhibited midazolam hydroxylation by rat liver and intestinal microsomes in vitro, with nanomolar K(i) values. At a total serum ketoconazole of 2 microg/ml (3.76 microM) in vivo, the predicted reduction in clearance of intragastric midazolam by ketoconazole (to 6% of control) was slightly greater than the observed reduction in vivo (to 15% of control). However, unbound serum ketoconazole greatly underpredicted the observed clearance reduction. Although the in vitro and in vivo characteristics of midazolam in rats incompletely parallel those in humans, the experimental model can be used to assess aspects of drug interactions having potential clinical importance.
Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Tufts-New England Medical Center, 136 Harrison Avenue, Boston, MA 02111, USA.
Tsutomu
T
Kotegawa
Bart E
BE
Laurijssens
Lisa L
LL
Von Moltke
Monette M
MM
Cotreau
Michael D
MD
Perloff
Karthik
K
Venkatakrishnan
Jill S
JS
Warrington
Brian W
BW
Granda
Jerold S
JS
Harmatz
David J
DJ
Greenblatt
D000465:Algorithms; D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D000935:Antifungal Agents / Q000493:pharmacokinetics* / Q000494:pharmacology*; D001711:Biotransformation; D001835:Body Weight / Q000187:drug effects; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004347:Drug Interactions; D007275:Injections, Intravenous; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000201:enzymology; D007441:Intubation, Gastrointestinal; D007654:Ketoconazole / Q000493:pharmacokinetics* / Q000494:pharmacology*; D008102:Liver Circulation / Q000187:drug effects; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D008874:Midazolam / Q000493:pharmacokinetics* / Q000494:pharmacology*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley
D014151:Anti-Anxiety Agents; D000935:Antifungal Agents; D003577:Cytochrome P-450 Enzyme System; D008874:Midazolam; D007654:Ketoconazole