Mammal Bites: “Answers”

1.  Which mammal bites get antibiotics?  Cat versus human versus dog?  Location of the bite?

From a Cochrane review of the topic, which looked at all known randomized controlled trials (RCTs) on the subject:

“The use of prophylactic antibiotics was associated with a statistically significant reduction in the rate of infection after bites by humans. Prophylactic antibiotics did not appear to reduce the rate of infection after bites by cats or dogs. Wound type, e.g. laceration or puncture, did not appear to influence the effectiveness of the prophylactic antibiotic. Prophylactic antibiotics were associated with a statistically significant reduction in the rate of infection in hand bites (OR 0.10, 95% CI 0.01 to 0.86; NNT = 4, 95% CI 2 to 50).”

2.  Which mammal bites do you close primarily and which do you leave open?  What’s your time window? Does it vary by mammal or location?

This is an area of controversy. A number of studies (including Chen, et al), have found that properly inspected, debrided, and irrigated wounds can be closed on most areas of the body with a 6-7% infection rate.  Hand wounds, cat bites, and human bites are associated with higher rates of infection, and therefore much more caution is warranted.  In terms of time window and type of closure, a rough consensus (open to much debate) is as follows:

Primary closure: head/face/neck/torso/proximal extremities (typically not hands and feet) lacerations, that occurred 12 hours or less from the time of presentation

Delayed primary closure: face and non-extremity wounds greater than 12 hours, or showing signs of infection. Typically, wound care is continued (debridement, antibiotics, etc.) for 72 hours, then the wound is re-evaluated for closure

No closure: Continuing infection, crush or puncture wounds, bites to the hands and feet, and clenched-fist injuries (fight bites)

3.  How do you irrigate bite wounds?  Do you use betadine?

Copiously.  You need about 7psi to irrigate most wounds. A 19-gauge or larger catheter with a 35-mL syringe is sufficient, as are most pedal sinks at full blast.  Most experts recommend 100-200mL of water per square inch for most wounds (i.e., not grossly contaminated).

According to Trott’s Wounds and Lacerations: Emergency Care and Closure, Betadine is one of the most potent bactericidal agents used in wound care. It is active against gram negatives, gram positives, fungi, and viruses. Betadine (povidone-iodine) comes as a 10% solution. It can be safely used to irrigate wounds only when diluted to a 1% concentration (i.e., a ten-fold dilution) or lower, as is evidenced by the ophthalmology literature.

4.  Which patients with bites do you admit?

Clearly, those going to the OR, or requiring IV antibiotics. We often admit the majority of our fight bites, in part because of patient reliability, and because of the high incidence of infection. The party line is:  consider admission in suspected tendon/joint/cartilage involvement; systemic infection; and in those unlikely to follow up.

References and Further Reading

Abrahamian FM, et al. Management of skin and soft tissue infections in the emergency department. Infect Dis Clin North Am. 2008; 22(1): 89-116.

Chen E, et al. Primary closure of mammalian bites. Acad Emerg Med. 2000; 7(2): 157-161.

Medeiros I and Saconato H. Antibiotic prophylaxis for mammalian bites. Cochrane Database Syst Rev. 2001; 2: CD001738.

Trott AT. Wounds and lacerations: emergency care and closure. Third edition. Mosby. 2005.

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2 Responses to Mammal Bites: “Answers”

  1. matt says:

    This site is very academic.

  2. marie says:

    Funny, when I think cat bites, tigers don’t come to mind.

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