Antibiotics for Prophylaxis of Animal Bites
Benefits in NNT
None were helped (infection prevented)
100% saw no benefit
0% were helped by avoiding infection
Harms in NNT
An unknown number were harmed (medication effects)
An unknown number were harmed by medication effects
Efficacy EndpointsProven bacterial infection plus positive microbiological cultures
Harm EndpointsNot reported
NarrativeMammals are known to harbor a variety of bacterial species in their oral cavities, and infections in mammalian bite wounds are both potentially aggressive and common. This raises an important question: can antibiotics, when given following a bite but before signs of infection, prevent skin and soft tissue infections?
This systematic review included eight randomized trials (total n = 522) six of which (n = 463) enrolled only subjects with dog bites. In the eight trials overall there appears to be no clear benefit to antibiotic use. Among the six trials examining only dog bites there was also no reduction in rates of infection (antibiotics - 4% [10/225] versus no antibiotics - 5.5% [13/238]).
Notably, the site of the bite was the most powerful predictor of infection: bites to the hand (3 studies) had a high rate of infection in the control group (28%), and in this small subgroup a beneficial effect of antibiotics was statistically significant [2% [1/61] vs 12/43], NNT = 4).
In addition, since the Cochrane review there has been a further reasonable quality trial addressing the question1. This study also found a low rate of infection (2%) and no significant benefit of prophylaxis.
CaveatsOverall, the event rate across studies was low (6.5%) and the number of subjects (522) is inadequate to determine whether antibiotic treatment significantly lowers infection rates. In addition, the enrolled sample is somewhat selected: superficial grazes and tendon and joint capsule injuries were excluded, and presumably all patients were treated with copious irrigation and wound cleansing. These factors may raise or lower infection rates when compared to wounds seen in community practice. In addition, multiple agents were used and it is not possible to draw conclusions about specific antibiotics.
The included studies of hand bites are of moderate to poor quality. While it is reasonable in practice to consider this the best available evidence (i.e. to treat with antibiotics prophylactically for hand wounds), this remains a ‘best guess’ with inadequate data.
These data do suggest the possibility of an as yet unproved preventive effect with prophylactic antibiotics for bite wounds in general. The enrollment numbers are too small to rule out a potentially important effect. Thus large, high quality, placebo-controlled randomized trials remain important and necessary to determine whether or not prophylactic antibiotics are appropriate. These studies are all the more important when considered in the context of the considerable side effect profile of antibiotics, which includes diarrhea, allergic reactions, and increasingly incident clostridium difficile infections. Therefore clinical equipoise between antibiotics and no treatment exists, and further studies are both ethical and necessary. This includes the subgroup of bite wounds that occur on the hand, where numbers are small and from studies of poor quality.