What is the validity of antitetanus (antitetanus) serum?

Validity of Antitetanus Serum

Antitetanus serum (tetanus immunoglobulin) provides short-term protection against tetanus for approximately 4 weeks, while animal-derived antitetanus serum is valid for only 7-10 days. 1

Duration of Protection

Tetanus immunoglobulin provides passive immunity with the following characteristics:

• Human tetanus immunoglobulin (TIG):

  • Provides protection for approximately 4 weeks 1
  • Standard dose is 250 units intramuscularly at a site different from toxoid injection 2
  • Causes fewer adverse reactions compared to animal-derived products 1

• Animal-derived antitetanus serum:

  • Provides protection for only 7-10 days 1
  • Associated with more undesirable reactions 1
  • Historical products (such as those from WWI) have been shown to lose their neutralization capacity over time 3

Efficacy and Limitations

The efficacy of tetanus immunoglobulin depends on several factors:

• Tetanus immunoglobulin works by neutralizing circulating tetanus toxin that has not yet bound to nerve tissue 2
• It cannot reverse toxin already bound to nerve endings 2
• A study examining a century-old vial of tetanus antiserum from World War I found that while IgG proteins were still present, they had lost their functional neutralizing capacity 3
• Even with seemingly protective antibody levels, rare cases of severe tetanus can occur, as documented in a case series of three immunized patients who developed grade III tetanus despite having high anti-tetanus antibody titers 4

Clinical Applications

For optimal tetanus prophylaxis in wound management:

1. For clean, minor wounds:

   • TIG is not indicated if the patient has received ≥3 doses of tetanus toxoid 5, 2
   • Tetanus toxoid booster is indicated if >10 years since last dose 5, 2

2. For tetanus-prone wounds (contaminated, puncture, or with devitalized tissue):

   • TIG is indicated for patients with unknown or <3 doses of tetanus toxoid 2
   • Tetanus toxoid booster is indicated if >5 years since last dose 5, 2

3. When both TIG and tetanus toxoid are indicated:

   • Administer simultaneously at different sites 6
   • This approach provides faster protection than either giving the first vaccination one month after the serum injection or mixing them together 6

Active vs. Passive Immunization

While antitetanus serum provides immediate but temporary protection, active immunization with tetanus toxoid is superior for long-term protection:

• After a primary immunization series with 3 doses of tetanus toxoid, virtually all infants and adults develop protective tetanus antitoxin titers >0.1 IU/mL 5
• A primary series provides protection for approximately 3-5 years 5
• Additional booster doses heighten the immune response and prolong protection, with booster doses at age 4-8 years and during adolescence providing protection for 20-30 years 5
• For adults, Tdap is preferred over Td for those who have not previously received Tdap 5

Common Pitfalls

• Relying solely on antitetanus serum without initiating active immunization in unvaccinated individuals 1, 6
• Assuming complete protection based on antibody titers alone, as rare cases of tetanus can occur despite seemingly protective levels 4
• Neglecting proper wound cleaning and debridement, which are as important as immunization in preventing tetanus 2
• Using outdated or improperly stored antitetanus serum products, which may have lost their neutralizing capacity 3

Remember that the minimum level of circulating antitetanus antibodies associated with protection is 0.01 IU/mL by in vivo toxin neutralization assay, while levels ≥0.1 IU/mL as measured by ELISA are generally considered protective 5, 7.