Antitetanus Serum (ATS) Dosing as Alternative to Tetanus Immunoglobulin (TIG)
When human Tetanus Immunoglobulin (TIG) is unavailable, equine Antitetanus Serum (ATS) can be administered at a dose of 1,500-3,000 IU intramuscularly for prophylaxis, or 10,000-20,000 IU for treatment of established tetanus, though this is significantly less preferred than TIG due to higher rates of allergic reactions and shorter duration of protection.
Critical Dose Equivalency Considerations
There is no direct dose equivalency between ATS and TIG - these are fundamentally different products with different potencies, pharmacokinetics, and safety profiles 1
The standard prophylactic dose of human TIG is 250 units IM for both adults and children, administered at a separate site from tetanus toxoid 1
When equine ATS must be used instead, the typical prophylactic dose ranges from 1,500-3,000 IU intramuscularly, which represents approximately 6-12 times the TIG dose numerically, though the biological activity differs 2, 3
Treatment vs Prophylaxis Dosing
For Prophylaxis (Wound Management)
Equine ATS prophylactic dosing: 1,500 IU intramuscularly or subcutaneously for standard tetanus-prone wounds 2
Higher doses of 10,000-20,000 IU may be considered for severe, heavily contaminated wounds or delayed presentation 4
Research from Ethiopia demonstrated that 1,500 IU of equine ATS had acceptable safety for prophylactic use, with only 1 severe local reaction among 1,213 patients (0.08% adverse event rate) 2
For Established Tetanus Treatment
For treatment of active tetanus disease, much higher doses are required: 10,000-20,000 IU of equine ATS administered intramuscularly 4
A Pakistani study found no significant mortality difference between 100,000 units and 20,000 units of ATS, suggesting 20,000 units is sufficient for most tetanus cases, with 100,000 units reserved for postpartum/abortion-related tetanus where infection is more generalized 4
Intrathecal administration of 1,500 IU of equine ATS combined with IV metronidazole showed superior outcomes compared to standard IM dosing in one study, with mortality of 11.7% vs 52% 3
Critical Safety Differences Between ATS and TIG
Human TIG is strongly preferred over equine ATS when available due to significantly lower risk of allergic reactions (anaphylaxis, serum sickness) and longer duration of protection 5
Equine ATS carries substantial risk of hypersensitivity reactions - always perform skin testing before administration and have epinephrine immediately available 2
The half-life and duration of protection differ substantially: human TIG provides protection for approximately 4 weeks, while equine ATS has a shorter duration of action 5
When ATS Might Be Considered
ATS should only be used when human TIG is unavailable, particularly in resource-limited settings where TIG supply is inadequate 1
In mass-casualty situations with TIG shortages, prioritize available TIG for persons aged >60 years and immigrants from regions other than North America or Europe, as these populations are less likely to have protective antibody levels 1
Essential Clinical Pearls
Always administer tetanus toxoid vaccine concurrently with either TIG or ATS, but at a separate anatomic site using a separate syringe to prevent interference with immune response 1
Neither TIG nor ATS can reverse damage from toxin already bound to neural tissue - they only neutralize circulating toxin 5
Patients receiving ATS or TIG still require completion of the primary tetanus vaccination series, as passive immunization does not confer long-term immunity 6, 5
Natural tetanus infection does not confer immunity, so even patients recovering from tetanus must receive active immunization with tetanus toxoid 5