Pharmacokinetics of moxalactam in elderly subjects

The pharmacokinetics of moxalactam were studied in 19 male volunteers 60 years of age or older with normal liver function tests and a creatinine clearance of greater than or equal to 60 ml/min. Moxalactam was administered in single or multiple intravenous or intramuscular doses. Rapid and complete intramuscular bioavailability was demonstrated in a subgroup of the study population. The mean plasma half-life was 2.9 +/- 0.8 h for intravenous doses and 3.5 +/- 0.9 h for intramuscular doses. Average renal clearances of 0.04 liters/kg per h accounted for 74.0 +/- 15.0% of total plasma clearance. Moxalactam plasma clearance showed a statistically significant (P less than 0.01) correlation with measured and calculated creatinine clearance. The major differences in moxalactam pharmacokinetics seen in the elderly appear to be related to diminishing renal function and highly variable nonrenal elimination. Creatinine clearance can be used in estimating moxalactam doses in the elderly without significant renal impairment, but recommendations for the use of serum creatinine as an estimation of renal function or drug half-life are not valid in this population group.