Plasma concentrations Average plasma concentrations of ertapenem following a single 30 minute intravenous infusion of a 1 g dose in healthy young adults (25 to 45 years of age) were 155 micrograms/ ml (Cmax) at 0.5 hour postdose (end of infusion), 9 micrograms/ ml at 12 hour postdose, and 1 microgram/ ml at 24 hour postdose.