A Cochrane review [Abstract] 1 included 8 studies with a total of 674 subjects. The bites were caused either by dogs (6 studies, n=614), cats (1 study, n=12) or humans (1 study, n=48). The antibiotics used were phenoxymethyl penicillin (2 studies), oxacillin (2 studies), dicloxacillin (2 studies), co-trimoxazole (1 study) or a choice of antibiotic for the treatment group (cephalexin or erythromycin in 1 study, cefaclor, cefazolin or penicillin G in 1 study). For dog bites, there was no statistically significant reduction of infection rate after the use of prophylactic antibiotics (4% vs. 5.5% in the control group; OR 0.74, 95% CI 0.30 to 1.85), whereas after bites by humans, the reduction in the infection rate was statistically significant (0/33 vs. 7/15 in the control group, p<0.05; n=48). All aggressors combined, there was no statistically significant difference between the rates of infections depending on whether or not prophylactic antibiotics were used (OR 0.49, 95% CI 0.15 to 1.58; statistically significant heterogeneity), but a meta-analysis using a fixed effects model resulted in an apparent benefit for the use of prophylactic antibiotics (OR 0.39, 95% CI 0.19 to 0.77). The infection rates for hand bites were significantly reduced by antibiotics (2% vs. 28% in the control group; OR 0.10, 95% CI 0.01 to 0.86; 3 studies; NNT=4, 95% CI 2 to 50).
The authors underline that the results should be interpreted with caution because considering the current knowledge on the bacteriology in bite wounds, the antimicrobial spectra of the studied antibiotics in the available studies has been inadequate.
Comment: The quality of evidence is downgraded by imprecise results (limited study size for each comparison), by inconsistency (heterogeneity in interventions and variability in results across studies) and by indirectness (possibly inappropriate antibiotics used in the trials).
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