Steady-state pharmacokinetics of ertapenem were compared in patients after 1-g intravenous and subcutaneous (s.c.) infusions. Bioavailability was 99%+/-18% after s.c. administration, but peaks were reduced by about (43+/-29 versus 115+/-28 microg/ml) and times to peak were delayed. Simulations based on unbound concentrations show that time over the MIC should always be longer than 30% to 40% of the dosing interval, suggesting that s.c. infusion could be an alternative in patients with reduced vascular access.