Diphtheria Antitoxin

Indications and Role:

Used for suspected cases of diphtheria. It should be given prior to bacteriological confirmation after testing for hypersensitivity to horse serum.

Testing for hypersensitivity:

  • Scratch, prick or puncture skin test: – clean skin and then scratch, prick or puncture the patients skin with a sterile needle and apply 1:100 dilution of the serum in normal saline in those without a history of animal allergy or prior exposure to animal serum (1:1000 is a positive history). Positive (histamine) and negative (saline) ID control should also be given. A positive result is one where the wheal with surrounding erythema is 3 mm larger than the control test (done with just saline) read at 15-20 mins and the patient has a positive read on the histamine patch.
  • Intra-dermal test: Give 0.02ml of 1:100 saline-diluted serum ID to creat a small wheal in those without a history of animal allergy or prior exposure to animal serum (1:1000 is a positive history). Positive (histamine) and negative (saline) ID control should also be given. A positive result is one where the wheal with surrounding erythema is 3 mm larger than the control test (done with just saline) read at 15-20 mins.
  • If positive for sensitisation then a desensitisation to DAT is required. IV regimen is below, each dose is given at 15 minute intervals:

Administration and dosing:

  • Dosing and manufacture instructions may vary so read the label.
  • Each 10ml Ampoule contains 10,000 IU
  • Dose according to clinical severity (20,000 – 120,000 units).
    • 20-40,000 for pharyngeal/laryngeal disease <48 hours
    • 40-60,000 for nasopharyngeal disease
    • 80-120,000 for >3 days of illness or diffuse neck swelling.
    • 20-40,000 skin lesions only after discussion with a specialist.
  • If skin testing is negative give the antitoxin dose in 250 – 500mL of 0.9% saline over 2 – 4 hours with monitoring for anaphylaxis. It can also be given intramuscular in mild to moderate cases.
  • If giving antitoxin all patients should also be receiving appropriate antibiotics – see diphtheria post.

Contraindications or complications and special populations:

  • Diphtheria antitoxin is based on horse serum and therefore severe and immediate anaphylaxis is a risk. Treat as per anaphylaxis with 0.5 ml of 1:1000 adrenaline intramuscularly every 5 minutes or with an intravenous infusion (follow local guidelines).
  • There is debate whether for cutaneous infection the risk of giving antitoxin outweighs the benefit therefore discuss with a specialist.
  • Fever – often mild and can be treated with antipyretics.
  • Serum sickness – 7 – 10 days post administration presenting with a flu-like illness, rarely angioedema, glomerulonephritis or Guillain-Barre syndrome. For serum sickness 50mg/day of prednisolone for adults and 1mg/kg in children for 7 days can ameliorate symptoms.

References

Dr Neil Long BMBS FACEM FRCEM FRCPC. Emergency Physician at Burnaby Hospital in Vancouver. Loves the misery of alpine climbing and working in austere environments. Supporter of FOAMed, toxicology, tropical medicine, sim and ultrasound

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