Interaction between midazolam and clarithromycin in the elderly.
OBJECTIVE
To assess the relative contribution of intestinal and hepatic CYP3A inhibition to the interaction between the prototypic CYP3A substrate midazolam and clarithromycin in the elderly.


METHODS
On day 1, 16 volunteers (eight male, eight female) aged 65-75 years weighing 59-112 kg received simultaneous doses of midazolam intravenously (i.v.) (0.05 mg kg(-1) over 30 min) and orally (p.o.) (3.5 mg of a stable isotope, (15)N(3)-midazolam). Starting on day 2, clarithromycin 500 mg was administered orally twice daily for 7 days. On day eight, i.v. and p.o. doses of midazolam were administered 2 h after the final clarithromycin dose. Serum and urine samples were assayed for midazolam, (15)N(3)-midazolam and metabolites by gas chromatography/mass spectometry.


RESULTS
Men and women exhibited similar i.v. (30.4 vs. 36.0 l h(-1)) and p.o. (119 vs. 124 l h(-1)) clearances of midazolam. Midazolam hepatic availability was significantly (P = 0.006) greater in men [0.79, 95% confidence interval (CI) 0.75, 0.84] than in women (0.66, 95% CI 0.59, 0.73), but midazolam intestinal availability (0.39 vs. 0.55) was not different. Following clarithromycin dosing, a significant decrease in systemic (33.2 l h(-1) to 11.5 l h(-1)) and oral (121 l h(-1) to 17.4 l h(-1)) midazolam clearance occurred. Oral, hepatic and intestinal availability was significantly increased after clarithromycin dosing from 0.34 to 0.72, 0.73 to 0.91 and 0.47 to 0.79, respectively. Clarithromycin administration led to an increase in the AUC of midazolam by 3.2-fold following i.v. dosing and 8.0-fold following p.o. dosing. Similar effects were observed for males and females.


CONCLUSIONS
Intestinal and hepatic CYP3A inhibition by clarithromycin significantly reduces the clearance of midazolam in the elderly.
Quinney
Sara K
SK
Division of Clinical Pharmacology, Indiana University School of Medicine, Wishard Memorial Hospital, W7123 Myers Building, Indianapolis, IN 46202-2879, USA.
Haehner
Barbara D
BD
Rhoades
Melissa B
MB
Lin
Zhen
Z
Gorski
J Christopher
JC
Hall
Stephen D
SD
D000284:Administration, Oral; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D014151:Anti-Anxiety Agents / Q000493:pharmacokinetics*; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics*; D017291:Clarithromycin / Q000493:pharmacokinetics; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004347:Drug Interactions; D005260:Female; D006801:Humans; D007275:Injections, Intravenous; D007422:Intestines / Q000201:enzymology*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008874:Midazolam / Q000493:pharmacokinetics; D012044:Regression Analysis
D014151:Anti-Anxiety Agents; D000900:Anti-Bacterial Agents; D003577:Cytochrome P-450 Enzyme System; D017291:Clarithromycin; D008874:Midazolam