Intramuscular tobramycin pharmacokinetics in geriatric patients

Twelve elderly institutionalized patients (mean age of 81 years) received intramuscular injections of tobramycin for infections at regular dosage intervals. The subjects had stable renal function but had limited mobility. Periodic blood specimens were collected for eight hours and analyzed for tobramycin by an immunofluorescence technique. The procedure was repeated in each patient one day later to detect day-to-day variability in the absorption kinetics. The absorption of tobramycin occurred primarily within two hours, although peak concentrations in some patients were indicative of a sustained plateau and exhibited intrapatient variability from one dose to the next. The time to peak and slowly declining concentrations suggest that the absorption process is extended in this population as compared to younger adults. Our data suggest that peak tobramycin concentrations following intramuscular injections to geriatric patients may be slightly delayed, though the extent of absorption appears to be consistent.