What is the treatment for Corynebacterium (diphtheria) infections?

Treatment for Corynebacterium diphtheriae Infections

The treatment for Corynebacterium diphtheriae infections requires prompt administration of diphtheria antitoxin (DAT) and antimicrobial therapy with either erythromycin (40 mg/kg/day for children; 1 g/day for adults) for 7-10 days or a single intramuscular injection of benzathine penicillin (600,000 units for persons <6 years old and 1,200,000 units for those ≥6 years old). 1

Core Treatment Components

1. Diphtheria Antitoxin (DAT)

• Must be administered as soon as diphtheria is suspected, without waiting for laboratory confirmation
• Neutralizes circulating toxin that has not yet entered cells
• Available through CDC's Emergency Operations Center (770-488-7100)
• Requires sensitivity testing before administration due to risk of allergic reactions
• Dosage depends on severity and duration of illness

2. Antimicrobial Therapy

Two primary options:

• Erythromycin:

  • Oral administration for 7-10 days
  • Children: 40 mg/kg/day
  • Adults: 1 g/day
  • May be slightly more effective than penicillin 1

• Benzathine Penicillin:

  • Single IM injection
  • Children <6 years: 600,000 units
  • Persons ≥6 years: 1,200,000 units
  • May be preferred due to guaranteed compliance (no risk of incomplete oral regimen) 1

Management of Contacts

For close contacts of diphtheria patients:

1. Obtain throat cultures regardless of vaccination status
2. Provide antimicrobial prophylaxis with the same regimens used for treatment
3. Monitor daily for 7 days for signs of disease
4. Update vaccination status:
   • For those with <3 doses or unknown status: immediate dose plus completion of primary series
   • For those with ≥3 doses but no booster in past 5 years: administer booster dose 1

Special Considerations

Antimicrobial Susceptibility

Recent studies show that while most C. diphtheriae remain susceptible to first-line antibiotics, approximately 4% of isolates show elevated MICs to erythromycin 2. Therefore, antimicrobial susceptibility testing may be warranted in cases that don't respond to initial therapy.

Invasive Infections

For bloodstream infections or other invasive forms of C. diphtheriae, the same antimicrobial regimens apply, but the role of antitoxin may be less clear when typical respiratory symptoms are absent 3. Clinical judgment is required in these cases.

Follow-up

• Repeat cultures after completion of antimicrobial therapy
• If cultures remain positive, administer an additional 10-day course of oral erythromycin 1

Pitfalls to Avoid

1. Delaying antitoxin administration: DAT should be given immediately upon clinical suspicion of diphtheria, as it only neutralizes circulating toxin and cannot reverse damage from toxin already bound to tissues.

2. Waiting for culture results: Treatment should begin empirically when diphtheria is suspected.

3. Inadequate contact tracing: All close contacts require evaluation and prophylaxis regardless of their vaccination status.

4. Neglecting vaccination: Ensure patients complete full vaccination series after recovery, as infection does not always confer immunity.

5. Overlooking non-respiratory presentations: C. diphtheriae can cause cutaneous infections and invasive disease including bacteremia and pneumonia without classic respiratory symptoms 4, 5.

By following this treatment approach, the mortality and morbidity associated with diphtheria infections can be significantly reduced.