A 6-year-old unvaccinated boy from rural India presents with a thick, adherent greyish-white pseudomembrane over the tonsils and pharynx, fever, and bull-neck appearance. Gram stain shows gram-positive bacilli. Which is the drug of choice for this patient?

Explanation

## Diphtheria Management: Antibiotic Choice **Key Point:** Benzylpenicillin G (Penicillin G) is the drug of choice for diphtheria. It has excellent tissue penetration and bactericidal activity against *Corynebacterium diphtheriae*. ### Treatment Regimen **High-Yield:** The standard regimen is: - **Benzylpenicillin G IV:** 50,000–100,000 units/kg/day in divided doses (4–6 hourly) for 7–10 days - **OR Erythromycin:** 40–50 mg/kg/day in divided doses for 7–10 days (alternative, especially if penicillin allergy) ### Critical Adjunct: Antitoxin **Clinical Pearl:** Diphtheria antitoxin (equine serum) must be given **immediately** on clinical suspicion — do NOT wait for culture confirmation. Antitoxin neutralizes circulating toxin but cannot reverse tissue damage already done. Timing is critical: antitoxin given within 48 hours of symptom onset dramatically reduces mortality and complications. **Mnemonic: ATTIC** — **A**ntitoxin **T**hen **T**reatment **I**s **C**ritical (give antitoxin first, then antibiotics) ### Why Penicillin G Over Alternatives | Feature | Benzylpenicillin G | Erythromycin | Cephalexin | | --- | --- | --- | --- | | **Tissue penetration** | Excellent | Moderate | Poor | | **Bactericidal activity** | Strong | Moderate | Moderate | | **First-line status** | Yes | Alternative | Not recommended | | **Carrier eradication** | Yes | Yes | No | | **Route** | IV (preferred) | Oral/IV | Oral only | **Key Point:** Erythromycin is an acceptable alternative in penicillin-allergic patients but is NOT first-line. Cephalexin (oral cephalosporin) has poor CNS penetration and is not suitable for systemic diphtheria. ### Supportive Management 1. **Airway protection:** Intubation if respiratory/laryngeal involvement 2. **Cardiac monitoring:** Watch for myocarditis (arrhythmias, heart block) 3. **Isolation:** Until two consecutive negative cultures post-treatment 4. **Immunization:** Vaccinate after recovery (infection does not always confer immunity) [cite:Park 26e Ch Communicable Diseases]