Controversies in antibiotic choices for bite wounds

In the last decade much progress has been made in our understanding of animal bites. Two major areas of remaining controversy are discussed. Recent study of human bites has shown that the early literature depicting all human bites as having an extraordinarily high infection and complication rate was biased by its emphasis on human bites of the hand that presented late with infection already present. These bites, the so-called closed-fist injuries (CFI), do indeed have a poor prognosis, but it may be as much due to their location and initial neglect as to the source of the injury. Human bites elsewhere do not seem to have any higher risk than animal bites, which have an infection rate of about 10%. Human bites of the face, lips, and ears are at very low risk for infection (less than 3%) if properly treated. The CFI should be identified early and aggressively irrigated and debrided (if possible). CFI wounds can be treated on an outpatient basis if uninfected and less than 24 hours old. The economical outpatient antibiotics of choice for CFI are penicillin plus dicloxacillin; the former is needed to cover Eikenella corrodens and the latter to cover Staphylococcus aureus , both common in these wounds. Diabetics with hand infection frequently have Gram-negative infection and may warrant parenteral aminoglycosides. Second- and third-generation cephalosporins are very effective but should be reserved for special situations due to their expense. Prophylactic antibiotics are not indicated for typical bite wounds, which are low risk. The choice of antibiotic (when needed) in other bite wounds is a matter of confusion, because the only scientific data available are in vitro sensitivities, which are a very poor and crude reflection of the clinical reality. Antibiotic effectiveness in vivo is dependent on a complex summation of absorption, tissue levels (not just serum levels), host immune defenses, and the interrelationships between bacterial species present. For dog bite wounds, dicloxacillin and cephalexin are both good choices because they cover most of the broad spectrum of infecting pathogens; dicloxacillin is significantly cheaper. If the patient is pencillin allergic, erythromycin is a good alternative. In cat bites, Pasteurella multocida is seen in up to 50% of infections. Some authors have claimed that dicloxacillin, oral cephalosporins, and erythromycin are not effective against this organism based solely on in vitro sensitivities, but in fact the clinical outcome is quite satisfactory with these antibiotics. Additionally, the clinician treating infection is almost never certain of the pathogen when starting treatment, and must therefore cover for the broad spectrum of organisms that may be seen. Tetracycline is effective against Pasteurella , but is otherwise a very poor choice in bite wound infection and should only be used in the case of proven Pasteurella infection or resistance to initial treatment. Amoxicillin/clavulanic acid, although touted for animal bites, has been examined only once in a very flawed study, which found it no more effective than dicloxacillin but possessing dramatically more complications. It costs three times as much as dicloxacillin, possesses no proven clinical advantage over this safer antibiotic, and cannot be recommended on the basis of current knowledge. Cefuroxime, a second-generation cephalosporin, can be given orally twice a day, and ceftriaxone (third-generation) can be given parenterally once a day, but both are unnecessary in most cases and cost up to 13 times as much as dicloxacillin.