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Bites - human and animal - Evidence
Evidence on antibiotic prophylaxis

  • Prophylactic antibiotics are effective for some bites. One systematic review found that that prophylactic antibiotics reduce the risk of infection after human bites. However a subsequent randomized controlled trial (RCT) found that antibiotic prophylaxis for low-risk human bites may not be necessary. There is no evidence that the use of prophylactic antibiotics is effective for cat or dog bites. There is evidence that the use of antibiotic prophylaxis after bites to the hand reduces infection, but confirmatory research is required.
  • A Cochrane review (search date: November 2000) identified eight RCTs (n = 522) that compared the use of an antibiotic with placebo or no treatment [Medeiros and Saconato, 2001]:
    • All studies assessed the use of antibiotics within 24 hours of the bite wound.
    • The populations were variable. Two studies included only children, two analyzed only adults, and three studies included both adults and children. One study did not specify an age group. All studies analyzed the incidence of infection. Four studies analysed the incidence of infection according to body part injured, three studies analyzed according to the type of wounds (lacerations, puncture, or avulsions).
    • In six studies the bites were caused by dogs, in one study bites were caused by cats, and in the other study the bites were caused by humans.
    • Several antibiotics were used as the intervention, including phenoxymethyl penicillin (two RCTs), oxacillin (two RCTs), dicloxacillin (two RCTs), co-trimoxazole (one RCT). In two studies a choice of antibiotic was given: cefalexin or erythromycin were used in one study; and ceclor, kefzol, or penicillin were used in another. Not all of these antibiotics may be appropriate for treating bites.
  • The results for the incidence of infection were as follows:
    • All bites. Pooled results from eight RCTs (n = 522) found that there was no difference between the rates of infections whether or not prophylactic antibiotics were used (OR 0.49, 95% CI 0.15 to 1.58).
    • Dog bites. Pooled results from six RCTs (n = 463) found that the infection rate was not reduced after the use of prophylactic antibiotics (4% [10/225]) compared with the control group (5.5% [13/238], OR 0.74, 95% CI 0.30 to 1.85).
    • Cat bites. One small study (n = 11) reported a lower infection rate in the treatment group who received prophylactic antibiotics (0% [0/5]) compared with the control group (67% [4/6]).
    • Human bites. Only one trial (n = 48) analyzed human bites, and the infection rate in the antibiotic group (0/33) was significantly lower than the infection rate in the control group (47% [7/15], OR 0.02, 95% CI 0.00 to 0.33).
  • The results for the site of the bite were:
    • Hand bites. Pooled results from three RCTs (n = 104) found that infection rates were significantly reduced by antibiotics (2% in the antibiotic group versus 28% in the control group) (OR 0.10, 95% CI 0.01 to 0.86; NNT = 4, 95% CI 2 to 50).
    • Head or neck bites. Pooled results from two RCTs (n = 82) found that infection occurred in only one patient in the control group, compared with no patients in the experimental group (OR 0.31, 95% CI 0.01 to 7.77).
    • Trunk bites. Pooled results from two RCTs found that infection was observed in only one patient in the experimental group and no patients in the control group (OR 1.80, 95% CI 0.04 to 79.4).
  • One subsequent small RCT (n = 127) compared a cefalexin/penicillin combination with placebo for preventing infection in low risk (penetrated only the epidermis and did not involve hands, feet, skin, overlying joints, or cartilaginous structures) human bites less than 24 hours old. Infection developed in 1 of 62 patients receiving placebo (1.6%, 95% CI 0.0 to 7.3%) and 0 of 63 patients receiving antibiotics (0%, 95% CI 0.0 to 4.6%). Antibiotic treatment of some low-risk human bite wounds could therefore be unnecessary since infection rates appear to be similar in low-risk human bite wounds whether treated with antibiotics or placebo [Broder et al, 2004].

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