Trimethoprim-sulphamethoxazole and metronidazole as prophylaxis in colorectal surgery: a study of bioavailability after an oral single dose.

OBJECTIVE: To evaluate oral single dose prophylaxis in colorectal surgery. DESIGN: Prospective study. SETTING: University hospital, Sweden. SUBJECTS: 24 patients (13 women; 11 men; mean age 57 years, range 27-81) listed for elective colorectal operations. INTERVENTION: At 0630 on the day of the operation all patients were given an oral dose of trimethoprim-sulphamethoxazole (TMP 160 mg and SMZ 800 mg) and metronidazole (2 g). The serum concentrations of TMP and SMZ were analysed in venous samples taken at the start and end of each operation. RESULTS: The earliest operation started at 0830 and the last finished at 1700. The median (range) serum concentrations of TMP were 1.4 (0.7-2.6) mg/L (start) and 1.3 (1.0-2.8) mg/L (end), and of SMZ 35 (15-65) mg/L (start) and 33 mg (13-70) mg/L (end). The individual values were above or equal to the minimal inhibitory concentration (TMP 0.8 mg/L; SMZ 15.2 mg/L) for relevant gram-negative species. CONCLUSION: Oral TMP/SMZ in the morning gives satisfactory serum concentrations independently of when the operation is done during the day. The regimen is simple and has the potential for being an effective alternative to intravenous prophylaxis.