Diphtheria Treatment
Immediate administration of diphtheria antitoxin combined with a 14-day course of erythromycin (40 mg/kg/day in children; 1g/day in adults) is the definitive treatment for active diphtheria infection, with antitoxin being critical to prevent mortality from toxin-mediated complications. 1, 2
Critical First Actions
Antitoxin must be given immediately upon clinical suspicion—do not wait for culture confirmation. 1, 2, 3 The antitoxin neutralizes circulating toxin but cannot reverse damage already done, making early administration the single most important determinant of survival. 1 Delayed antitoxin administration is associated with high mortality even with appropriate antibiotic therapy. 3
Antitoxin Administration Protocol
- Perform sensitivity testing before administering equine diphtheria antitoxin due to 7% risk of immediate hypersensitivity reactions and 5% risk of serum sickness. 4, 1
- Dosing: 5,000-10,000 units IM at a site different from toxoid injection. 4, 2
- Antitoxin can be obtained from manufacturers (Connaught Labs, Inc., or Sclavo, Inc.) or the CDC Division of Immunization (telephone: 404-639-2888). 4
Antimicrobial Therapy
Erythromycin is the preferred antibiotic for eliminating the organism and preventing toxin production. 1, 2
Antibiotic Options
First-line: Oral erythromycin for 14 days
Alternative: Benzathine penicillin G as single IM injection
Follow-Up Culture Verification
- Obtain follow-up cultures after completing antimicrobial therapy. 2
- If cultures remain positive: Administer an additional 10-day course of oral erythromycin and repeat cultures. 4, 2
- This is critical as 21% of carriers relapse after initial 6-day erythromycin courses. 5
Management of Close Contacts
All close contacts require immediate antimicrobial prophylaxis regardless of vaccination status—do not wait for culture results. 4, 2, 6
Contact Identification
- All household members
- Persons with habitual close contact with the patient
- Anyone directly exposed to oral secretions
Prophylaxis Protocol
Antimicrobial prophylaxis: 4, 6
- Benzathine penicillin G IM (preferred for compliance): 600,000 units (<6 years) or 1,200,000 units (≥6 years) 4, 6
- OR oral erythromycin for 7-10 days: 40 mg/kg/day (children) or 1g/day (adults) 4, 6
- Contacts with <3 doses or unknown vaccination status: Immediate dose of age-appropriate diphtheria toxoid-containing vaccine and complete primary 3-dose series 4, 6
- Contacts with ≥3 documented doses: Booster dose if last dose was >5 years ago 4, 6
- Obtain cultures from all close contacts 4
- Daily clinical examination for 7 days watching for pharyngeal symptoms, fever, and membrane formation 4, 6
Common Pitfalls to Avoid
- Never delay antitoxin while awaiting culture results—clinical suspicion alone warrants immediate treatment. 1, 2, 3 Mortality remains very high without immediate antitoxin administration. 3
- Do not use antibiotics alone—they eliminate the organism but do not neutralize circulating toxin. 1, 7 Antibiotics must be paired with antitoxin to limit morbidity. 7
- Do not assume vaccinated contacts are protected from transmission—vaccination reduces transmission by only 60% and vaccinated individuals can become colonized and transmit. 7 All contacts require antimicrobial prophylaxis. 6
- Do not use shorter antibiotic courses—14 days is required for active infection, as shorter courses (6 days) result in 21% relapse rates. 5
- Do not skip follow-up cultures—reculture at minimum 2 weeks after therapy completion to ensure organism eradication. 4, 5
Special Considerations
Cutaneous Diphtheria
- If toxigenic strain confirmed: Same antimicrobial regimen and contact investigation as respiratory diphtheria 4, 1
- If nontoxigenic strain: Routine contact investigation not necessary 4
Immunocompromised Contacts
- Warrant more aggressive surveillance, completion of full antimicrobial prophylaxis course, and vaccination according to immunocompromised schedules 6