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.