Metronidazole single versus multiple daily dosing in serious intraabdominal/pelvic and diabetic foot infections.

The purpose of the study was to compare the clinical efficacy of once-daily versus multiple dose regimens of metronidazole in inpatients with serious/systemic Bacteroides fragilis infections, i.e., intraabdominal/pelvic and diabetic foot infections. A retrospective chart review was performed on 145 adult inpatients who received combination therapy with metronidazole for B. fragilis abdominal/pelvic infection or diabetic (deep) foot infections/osteomyelitis. Exclusion criteria included metronidazole given for indications other than those mentioned, patients who received only one dose of metronidazole, and patients who received oral metronidazole only. The 145 patients were in two groups: 66 patients in the metronidazole 1 g (i.v.) q24h (Group A) and 79 patients who received metronidazole 500 mg (i.v./p.o.) q6-8h dosing (Group B). Patient demographics included age, gender, indications of metronidazole, concomitant, antibiotics, and co-morbidities. Data collection also included length of stay (LOS), antibiotic days, and clinical outcomes. The 145 patients in our study had a mean age of 66 years, 61% were female and 39% male. Most patients were being treated for definitive intraabdominal/pelvic infections (82%), or probable intraabdominal/pelvic infections (22%). Only 6% had deep diabetic foot infections of osteomyelitis (percentages exceed 100% since a patient can have more than one indication) and were included since B. fragilis is also and important pathogen in diabetic osteomyelitis. Group A patients had more concomitant antibiotics and co-morbidities (p < 0.0001 and p < 0.05 respectively, chi-square test for trend) than Group B patients. There were no statistically significant differences between groups A and B for LOS and antibiotic days (p = 0.42 and p = 0.92 respectively, by rank-sum test), but after adjusting for concomitant antibiotics and co-morbidities Group A patients had clinically shorter LOS and fewer antibiotic days. Unadjusted mortality and failure rates were non-significantly higher in group A (relative ratios of 12.1%/6.3% = 6.3% = 1.91 and 18.2%/ 10.1% = 1.80 respectively), but after adjusting for concomitant antibiotics and co-morbidities with stratification analysis, groups A and B were virtually the same (risk differences of </= 1%). The authors conclude that for B. fragilis infections, as part of combination therapy, metronidazole 1 g (i.v.) q 24h appears to eb as efficacious and not inferior to multiply-dosed metronidazole regimens. Once daily metronidazole, i.e., 1 g (i.v.) q24h for the treatment of serious systemic infections where B. fragilis is an important co-pathogen (intraabdominal/pelvic and deep diabetic foot infections) has pharmacokinetic and pharmaco-economic advantages.