CAT BITE Antibiotic Prophylaxis for the Hand/Forearm (CATBITE)

Cat bites have been reported as the second most common domestic animal bite in the United States, ranging from 5%-15% of all bites. The hand is the most common site of bite injuries. Cat bites are puncture wounds that have the potential to seed bacteria deep within the joint capsule, periosteum and bone. As a result, infection is a serious complication, reported in 30%-50% of cat bites. The median time to signs and symptoms of infection following a cat bite is typically short (approximately 12 hours). Direct healthcare costs associated with management of cat and dog bites in the United States estimate >$850,000,000 annually and do not consider the indirect costs associated with time off work, rehabilitation, and permanent impairment.

The average cat bite wound culture yields five types of bacterial isolates. Mixed aerobic and anaerobic bacteria are observed in 60% of cases. Pasteurella multocida is the is the most common organism isolated from the mouths of cats that can cause infections after a bite. Pasteurella species are isolated from 75% of cat bite wounds, and the incubation period for Pasteurella infection is one to three days. Capnocytophaga canimorsus can cause bacteremia and fatal sepsis after animal bites, especially in patients with asplenia, alcoholism, or underlying hepatic disease. The incubation period for Capnocytophaga infection is one to three days. Bartonella henselae may be transmitted via the bite of an infected cat and contact with cat saliva via broken skin or mucosal surfaces. The incubation period for Bartonella infection is 7 to 14 days. Anaerobes isolated from dog and cat bite wounds include Bacteroides species, fusobacteria, Porphyromonas species, Prevotella species, cutibacteria (formerly propionibacteria), and peptostreptococci.

Prophylactic antibiotics are often recommended to decrease the incidence of developing an infection. Broad antibiotic coverage is recommended to address the polymicrobial nature of common oral flora and bite infections. Pasteurella species are generally susceptible to penicillin and ampicillin, but staphylococci and anaerobic species often produce beta-lactamase, which provides resistance to these antibiotics. Adding a beta-lactamase inhibitor significantly increases the effectiveness of these antibiotics, and amoxicillin-clavulanate is the oral antibiotic of choice for human, dog, and cat bites. Infectious Diseases Society of America (IDSA) guidelines recommend antibiotic prophylaxis with amoxicillin-clavulanate 875-125mg twice daily (BID) for 3-5 days or ciprofloxacin 500-750mg BID + clindamycin 300-450mg three times daily (TID) if a participant has a penicillin allergy. However, only one randomized controlled clinical trial (RCT) has been performed to date to assess the efficacy of prophylactic antibiotics following cat bites. Adult participants with uninfected full-thickness wounds presenting within 24 hours of injury to the emergency department were considered. Participants were randomly assigned to receive oxacillin 500mg four times daily (QID) for five days (n=5) or identically appearing placebo (n=6). Four of six participants receiving placebo, but none of the five participants receiving oxacillin, developed a wound infection (P = 0.045).

Immunocompetent adult participants presenting within 24 hours of a cat bite without any signs or symptoms of infection may benefit from advances in wound care alone or only need a maximum of 24 hours of antibiotic prophylaxis. Furthermore, a Cochrane review aggregating data from clinical trials from the literature concluded, "There is no evidence that the use of prophylactic antibiotics is effective for cat or dog bites." The investigators' hypothesis is that administration of 5 days of prophylactic antibiotics will not reduce the incidence of infection in participants evaluated and treated within 24 hours of cat bite injury, who do not exhibit signs of an active infection.