Previously reported clinical trials of imipenem-cilastatin 500 mg given intravenously every 6 hours (intravenous group) and imipenem-cilastatin 750 mg given intramuscularly every 12 hours (intramuscular group) were analyzed for relative cost savings. Acquisition costs were significantly higher for the intravenous group for intravenous supplies (30.6 +/- 7.9 dollars) when compared to the intramuscular group (0.98 +/- 0.03 dollars) (p less than 0.05). Also, significantly higher cost (p less than 0.05) was noted for salaries of pharmacists and technicians for manufacturing in the intravenous group (5.8 +/- 1.5 dollars) as compared to the intramuscular group (2.4 +/- 0.7 dollars). Nursing administration costs were greater for the intramuscular group (15.6 +/- 4.8 dollars) when compared to the intravenous group (11.7 +/- 3.0 dollars). Incorporating all appropriate costs, the mean total drug therapy costs (TRX$) were significantly greater (p less than 0.01) for the intravenous group (458.17 +/- 175.17 dollars) as compared to the intramuscular group (298.0 +/- 114.76 dollars). Thus, the dosing of imipenem-cilastatin 750 mg intramuscularly every 12 hours is a more cost effective method of drug delivery with equal efficacy and safety when compared to imipenem-cilastatin 500 mg given intravenously every 6 hours.