Why we do what we do: Antibiotics for dog bites

For a long time when encountering a patient who had suffered a dog bite I reflexively placed the patient on antibiotics. Generally, either amoxicillin/clavulanate or clindamycin. Along the way I began to question whether or not there is evidence to support this practice, since I also haven’t seen many infected dog bites. As you may already be aware, most dog bites are from an animal known to the victim. One study from Australia noted that >4/5 were known. In children under 5 the bites are more likely to be in the head/neck (60-70%). See Patronek at al. for more. In older children and adults the extremities – more commonly the dominant hand – are involved.

The exact rate of infections is hard to estimate since many patients with dog bites likely do not seek care. But, in those that do seek care >24 hours after the bite the rate of infections seems to be higher. Overall though, infections from dog bites are more infrequent than almost any other animal – see Capellan from Emerg Med Clin North Amer for more. If a wound needs to be closed copious irrigation is a must. Debriding dead/compromised tissue is key, as is avoiding deep sutures and any tissue adhesive. It is OK to allow the wound to drain. Ultimately, despite these practices I still wonder whether or not antibiotics truly make a difference. This is, unfortunately, where the literature is a bit thin.

Dog-bite lacerations: a controlled trial of primary wound closure
C Maimaris and D N Quinton
Arch Emerg Med. 1988 Sep; 5(3): 156–161

This was randomized trial of 96 patients of all ages (though most were <30 years). Together they had 169 dog bites. 92/169 were closed and 77/169 were not. No patient got antibiotics. Overall 13/169 wounds developed infection – with no difference between sutured or not (7.6 versus 7.8 percent).

Antibiotics to prevent infection in patients with dog bite wounds: a meta-analysis of randomized trials
Cummings, P
Ann Emerg Med. 1994 Mar;23(3):535-40.

Eight randomized trials were reviewed with the cumulative incidence of infection in controls 16%. The relative risk for infection in antibiotics vs not was RR=0.56 (95% CI, 0.38 to 0.82). The number needed to treat was approximately 14.

Relative risk estimates and 95% CI for individual studies and the summary relative risk estimate for all studies. A relative risk estimate less than 1.0 indicates that antibiotic treatment reduces the risk of infection. The reference number is given for individual studies. *Study has a relative risk estimate of infinity.

Relative risk estimates and 95% CI for individual studies and the summary relative risk estimate for all studies. A relative risk estimate less than 1.0 indicates that antibiotic treatment reduces the risk of infection. The reference number is given for individual studies. *Study has a relative risk estimate of infinity.

Primary closure of mammalian bites
Chen et al.
Acad Emerg Med. 2000 Feb;7(2):157-61.

This observational study evaluated 145 bites that underwent primary closure. Dogs made up more than half 88/145, but cat and human bites weer also included muddying the waters a bit with regard to the question at hand. majority of the wounds (57 percent) were on the head and neck. Only 8 patients (5.5%) developed infection despite having received antibiotics. The study was purely descriptive.

Antibiotic prophylaxis for mammalian bites
Medeiros et al.
Cochrane Database Syst Rev. 2001

This Cochrane review of 8 RCTs trials saw no statistically significant reduction of local wound infection in antibiotic prophylaxis (4%, 10 of 225 patients) versus controls (5.5%, 13 of 238 patients). The odd ratio was 0.74 (95% CI 0.30 to 1.85). Subanalysis did show that antiobiotic prophylaxis lowered the rate of infection in dog bites of the hand – 28% to 2%, with an OR = 0.10 (95% CI 0.01 to 0.86). The number needed to treat for hand infections was 4.

Primary repair of facial dog bite injuries in children
Wu et al.
Pediatr Emerg Care. 2011 Sep;27(9):801-3.

This descriptive report of 87 consecutive patients under age 18 with dog bite facial injuries, all of which received an antibiotic. None developed wound infection.

Why did I choose this topic for a Why We Do What We Do? Well, I do feel that this is an area where we practice reflexively. There really is limited evidence for what seems to be a routine practice. I do suspect that there is a bias towards patients who seek care in an ED/office. There are probably thousands of dog bites that happen at home and do not result in an ED visit. Do those get infected? Probably not in all honesty. Nevertheless, I am left in a bit of a quandry, as I feel that we should always be practicing evidence based medicine. So, based on the available literature it makes sense to put patients on prophylactic antibiotics for a dog bite wound if;

  • The wound has been primarily closed
  • Moderate to severe wounds (crush injury, devitalized or missing tissue, deep bites to tendons or bone)
  • Puncture wounds
  • Bites to the hands, feet, genitals or face
  • Asplenic or immunocompromised patients

If you are going to prescribe antibiotics (though not the exact focus of this post), I would use Amoxicillin/clavulanate, a broad spectrum cephalosporin if penicillin allergic, or clindamycin. If you aren’t going to prescribe prophylactic antibiotics have a good discussion with the patient and their family.

By |2016-12-14T12:56:38+00:00May 31st, 2016|Infectious Diseases, Procedures, Surgery|

About the Author:

Brad Sobolewski, MD, MEd is an Associate Professor of Pediatric Emergency Medicine and an Assistant Director for the Pediatric Residency Training Program at Cincinnati Children's Hospital Medical Center. He is on Twitter @PEMTweets and authors the Pediatric Emergency Medicine site PEMBlog. All views are strictly my own and not official medical advice.