Pharmacokinetic and pharmacodynamic approach for comparing two therapeutic regimens using amikacin

The efficiencies of two dosage schedules of amikacin (2 x 10 mg/kg of body weight per 24 h and 1 x 20 mg/kg/24 h intramuscularly for 5 days) against Pseudomonas aeruginosa sepsis in rabbits were compared. Blood samples were drawn at various times after the first application, and amikacin concentrations in serum were assayed microbiologically. The dynamics of the bactericidal effect of amikacin was simulated in vitro with the same strain of P. aeruginosa. No regrowth was found with the 20-mg/kg dose when the bacterial inoculum was in contact with experimental and theoretically predicted serum amikacin concentrations. The killing effect was present even when the drug levels decreased considerably below the MIC. The interrelationship between simulated amikacin concentrations in serum and the corresponding average killing rates was described appropriately by the standard Emax model. The higher amikacin dose performed its bacterial effect faster and the drug persisted longer in the blood. The two amikacin regimens were therapeutically equivalent, but the once-daily schedule had some advantages over the twice-daily drug administration which became evident when both the pharmacokinetic and the pharmacodynamic parameters of the drug were considered.