Age-associated pharmacokinetic changes of metronidazole.

Serum concentration and urinary excretion of metronidazole were determined after p.o. administration of 500 mg to 15 young (20-25 years old) and 20 elderly (over 70) subjects. Serum levels were consistently higher and the AUCs were almost doubled in the aged group. One of the effects underlying the decrease in total clearance is the diminished renal excretion; however, the role of the reduction of distribution volume seems to be more important. Red cell binding of metronidazole significantly decreased in the aged group; this may also contribute to the reduction of distribution volume. Reduction of the standard dose of metronidazole by 30-40% is recommended in elderly patients.