Are We Using the Correct Dose of Metronidazole in Colorectal Surgery?

In a series of 20 patients undergoing elective colorectal surgery, 10 received an infusion of metronidazole 500 mg and 10 an infusion of 1500 mg commencing at the induction of anaesthesia. The concentrations of metronidazole in the plasma, rectus muscle and colon of the two groups during the course of the operation were compared. In those patients who received 1500 mg, the plasma and tissue concentrations were all well above the minimum inhibitory concentration (MIC) of metronidazole against Bacteroides fragilis. In those patients who received 500 mg, serum and tissue concentrations were at or only just above the MIC. It may be that 1500 mg would be a more effective dose of metronidazole for prophylactic use in colorectal surgery.