Emergency Medicine Hub / Ambulatory & Fast Track • 3 min read • 4 sections

Animal & Human Bites & Tetanus Prophylaxis

Evidence-based emergency management of mammalian bite wounds, rabies post-exposure prophylaxis (PEP), and acute tetanus prevention. Covers the distinctive microbiology of dog, cat, and human bites (Pasteurella, Capnocytophaga, Eikenella), fight bite extensor tendon mechanics, rabies risk assessment and HRIG/vaccine administration, first-line antimicrobial dosing (Augmentin vs. penicillin-allergic regimens), and primary vs. delayed closure rules.

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

Wound Closure Rule

Cat bites, puncture wounds, human bites, bites to hands/feet, and wounds > 12-24 hours old must NEVER be closed primarily. High-pressure irrigation is the single most vital intervention.

Antibiotic of Choice

Amoxicillin-clavulanate (Augmentin) 875/125 mg PO BID for 3-5 days prophylaxis (7-10 days if infected).

Penicillin-Allergic Alternative

Doxycycline 100 mg PO BID OR Ciprofloxacin 500 mg PO BID PLUS Metronidazole 500 mg PO TID. (Cephalexin, Clindamycin, and Macrolides alone fail against Pasteurella).

Fight Bite Protocol

Closed-fist laceration over dorsal MCP joint; examine in flexion; obtain X-rays for tooth foreign bodies and joint air; admit for IV Ampicillin-sulbactam and emergent hand surgery consult.

Capnocytophaga Alert

Dog saliva exposure in asplenic or cirrhotic patients can precipitate catastrophic purpura fulminans, septic shock, and DIC within 24-48 hours; initiate immediate empiric Augmentin.

Rabies PEP

Unvaccinated patient = HRIG (20 IU/kg infiltrated around wound) + 4 vaccine doses (1.0 mL IM in deltoid on Days 0, 3, 7, 14). Observe domestic dog/cat for 10 days; if healthy, no PEP required.

Tetanus Booster

Dirty/contaminated wound gets Tdap if last dose > 5 years ago; add TIG 250 units IM if < 3 lifetime doses or unknown status.

Bottom-Line Clinical Pearl

Cat bites have a 50-80% infection rate due to needle-sharp teeth that inoculate Pasteurella multocida directly into tendon sheaths and periosteum; ALL cat bites require prophylactic oral Augmentin and must NEVER be closed primarily. In human 'fight bites' over the MCP joint, always examine the wound in full flexion and assume septic arthritis until ruled out.

1. Mammalian Bite Microbiology & Clinical Stratification

Bite wound pathophysiology is determined by the mechanical nature of the trauma (puncture vs. crush/avulsion) and the unique polymicrobial oral flora of the biting species:

Bite Exposure	Predominant Pathogens	Infection Risk & Mechanism	Emergency Management & Closure Rules
Cat Bites (Feline)	Pasteurella multocida (75-90%), Staphylococcus aureus, oral anaerobes	50% to 80% infection rate. Slender, needle-sharp teeth cause deep, inoculating puncture wounds with rapid clinical onset (< 12-24 hours) leading to tenosynovitis or osteomyelitis	DO NOT SUTURE. Copious high-pressure syringe irrigation; splint in position of function. MANDATORY prophylactic Augmentin 875/125 mg BID x 5 days for ALL cat bites.
Dog Bites (Canine)	Pasteurella canis, Capnocytophaga canimorsus, S. aureus, Streptococcus, anaerobes	15% to 20% infection rate. Large crushing and tearing forces causing devitalized tissue, jagged lacerations, and shearing pockets	Debride devitalized tissue; irrigate. Facial wounds may be closed loosely after copious irrigation (cosmetic priority + high vascularity). Hand/foot wounds left open. Prophylaxis for high-risk wounds.
Human 'Fight Bite' (Clenched Fist)	Eikenella corrodens, Viridans group streptococci, S. aureus, Fusobacterium, Peptostreptococcus	Very high infection rate (30-50%). Severe destructive necrotizing enzymes; tooth punctures dorsal MCP joint capsule	NEVER CLOSE. Examine MCP joint in full flexion. Plain X-rays to rule out fracture or embedded tooth fragment. Splint in safe position. IV Ampicillin-sulbactam and hand surgery consultation.
Capnocytophaga canimorsus Exposure	Capnocytophaga canimorsus (commensal in 74% of dogs and 57% of cats)	Overwhelming fulminant sepsis, purpura fulminans, symmetrical peripheral gangrene, and DIC in ASPLENIC or CIRRHOTIC hosts	Even minor dog licks or scratches on abraded skin in an asplenic patient mandate immediate prophylactic Augmentin or IV Ceftriaxone.

Critical Board Trap: The Human 'Fight Bite'

A human fight bite occurs when a clenched fist strikes an opponent's teeth, puncturing the skin and extensor tendon over the 3rd or 4th metacarpophalangeal (MCP) joint. When the hand is subsequently relaxed into extension, the lacerated extensor hood retracts proximally, carrying aggressive oral bacteria (Eikenella corrodens) deep into the subaponeurotic space and MCP joint cavity. A benign-looking 5 mm skin tear can progress to joint destruction and permanent digital stiffness within 48 hours. ALWAYS examine wounds in full fist flexion; obtain plain X-rays; splint in intrinsic-plus position; NEVER close.

2. Antimicrobial Regimens: First-Line & Penicillin-Allergic

Clinical Scenario	First-Line Regimen	Penicillin-Allergic Regimen	Major Ineffective Antibiotics (AVOID)
Outpatient Prophylaxis (Dog, Cat, or Human)	Amoxicillin-Clavulanate (Augmentin) 875/125 mg PO BID x 3-5 days (Pediatric: 45 mg/kg/day divided BID)	Doxycycline 100 mg PO BID OR (Ciprofloxacin 500 mg PO BID + Metronidazole 500 mg PO TID) OR (TMP-SMX DS 1 tab BID + Clindamycin 300 mg TID)	DO NOT USE: Cephalexin, Cefaclor, Clindamycin monotherapy, Erythromycin, or Vancomycin monotherapy (all have POOR or ZERO activity against Pasteurella multocida).
Inpatient/Severe Established Infection	Ampicillin-Sulbactam (Unasyn) 1.5 to 3.0 g IV every 6 hours OR Piperacillin-Tazobactam 3.375 g IV q6h	Ceftriaxone 1-2 g IV daily + Metronidazole 500 mg IV q8h OR Levofloxacin 500 mg IV + Metronidazole 500 mg IV	Avoid aminoglycosides (ineffective against anaerobes and Pasteurella).

3. Rabies Post-Exposure Prophylaxis (PEP) Algorithm

Rabies has the highest case-fatality rate of any infectious disease (> 99.9% once neurological symptoms appear). Post-exposure prophylaxis must be evaluated based on the animal species, geographic risk, and vaccination status:

Animal Category	Exposure Circumstance	Mandatory Rabies Action
High-Risk Wild Mammals (Bats, Raccoons, Skunks, Foxes, Coyotes)	Any bite, scratch, direct contact, or waking up in a room with a bat without a witness confirming no contact	IMMEDIATE PEP REQUIRED. If animal is captured, euthanize immediately and submit intact brain for direct fluorescent antibody (DFA) testing; discontinue PEP if test is negative.
Domestic Dogs, Cats, and Ferrets	Healthy, available for 10-day quarantine by animal control	DO NOT START PEP IMMEDIATELY. Quarantine and observe animal for 10 days. If animal remains healthy and normal throughout 10 days, rabies transmission was impossible; no PEP needed. If animal becomes sick or displays rabies signs, begin immediate PEP and test animal.
Stray or Escaped Domestic Dogs/Cats	Unprovoked bite; animal escaped and cannot be quarantined	INITIATE FULL PEP REGIMEN IMMEDIATELY in consultation with local public health department.
Low-Risk Mammals (Squirrels, Hamsters, Guinea Pigs, Gerbils, Chipmunks, Rats, Mice, Rabbits)	Standard bites or scratches	Rabies PEP is ALMOST NEVER INDICATED. Small rodents are virtually never infected with rabies and their bites do not transmit the virus.

Patient History	Human Rabies Immune Globulin (HRIG)	Rabies Vaccine (HDCV or PCECV)
Previously UNVACCINATED Patient	20 IU/kg body weight ONCE on Day 0. Infiltrate as much of the full dose as anatomically feasible directly in and around all wound margins. Inject any remaining volume IM at an anatomical site DISTANT from the vaccine (e.g., contralateral thigh). Never inject HRIG in the same syringe or same limb as the vaccine.	4-Dose Series: 1.0 mL IM administered on Day 0, Day 3, Day 7, and Day 14. Administer in the DELTOID muscle in adults/older children (anterolateral thigh in infants). NEVER administer rabies vaccine in the GLUTEAL muscle (causes lower antibody titers and failure). Immunocompromised patients receive a 5th dose on Day 28 with serologic testing.
PREVIOUSLY VACCINATED Patient (Documented prior complete PEP or pre-exposure series)	DO NOT ADMINISTER HRIG (anaphylaxis and antibody blunting risk).	2-Dose Series: 1.0 mL IM in deltoid on Day 0 and Day 3 only.

4. CDC Tetanus Prophylaxis Decision Matrix

Patient Tetanus Vaccination History	Clean, Minor Wounds: Tetanus Toxoid (Tdap/Td)	Clean, Minor Wounds: TIG (Tetanus Immune Globulin)	Contaminated/Dirty Wounds (Punctures, Bites, Soil): Vaccine	Contaminated/Dirty Wounds: TIG
Unvaccinated, < 3 Lifetime Doses, or Unknown	YES (Tdap preferred)	NO	YES (Tdap preferred)	YES: Administer Tetanus Immune Globulin (TIG 250 units IM) at separate anatomical site
>= 3 Lifetime Doses: Last dose < 5 years ago	NO	NO	NO	NO
>= 3 Lifetime Doses: Last dose 5 to 10 years ago	NO	NO	YES (Give Tdap or Td booster)	NO
>= 3 Lifetime Doses: Last dose > 10 years ago	YES (Give Tdap or Td booster)	NO	YES (Give Tdap or Td booster)	NO

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