A 6-year-old unvaccinated child from rural India presents with a thick, adherent, greyish-white pseudomembrane over the tonsils and pharynx, fever, and difficulty swallowing. Culture confirms Corynebacterium diphtheriae. Which is the drug of choice for treatment?

## Management of Diphtheria: Drug of Choice **Key Point:** In diphtheria, **Diphtheria Antitoxin (DAT)** is the single most critical intervention, but among antibiotics, **Erythromycin** (orally or parenterally) is the drug of choice per standard references (IAP, Nelson's, Park's Textbook of Preventive & Social Medicine). Penicillin G is an acceptable alternative, but erythromycin is preferred. ### Why Erythromycin is the Antibiotic of Choice **High-Yield:** According to Nelson's Textbook of Pediatrics and IAP guidelines: - **Erythromycin** (40–50 mg/kg/day orally in 4 divided doses, max 2 g/day for 14 days) is the **first-line antibiotic** for diphtheria. - It achieves excellent tissue penetration in the pharynx and respiratory tract. - It is superior to penicillin in eradicating the carrier state. - Penicillin G (benzylpenicillin) is listed as an **alternative**, not the drug of choice. ### Role of Diphtheria Antitoxin (DAT) **Clinical Pearl:** DAT (equine-derived) is the **most important** and **life-saving** treatment — it neutralizes circulating exotoxin before it binds to tissues. However, DAT is a biological product (antitoxin), not a "drug" in the antibiotic sense. When the question asks for "drug of choice for treatment," in the context of antibiotic therapy, erythromycin is the answer. DAT must always be given concurrently. | Agent | Role | |---|---| | Diphtheria Antitoxin | Neutralizes toxin — mandatory, given ASAP | | Erythromycin | **Drug of choice antibiotic** — eradicates organism, prevents spread | | Penicillin G | Alternative antibiotic | | Cephalexin | Not recommended | ### Complete Treatment Regimen 1. **Antitoxin:** 20,000–100,000 units IM/IV (based on severity) 2. **Antibiotic:** Erythromycin 40–50 mg/kg/day × 14 days (first-line); Penicillin G as alternative 3. **Supportive care:** Airway management, cardiac monitoring for myocarditis 4. **Isolation:** Until two consecutive negative cultures post-treatment **Mnemonic: "E for Erythromycin = E for Eradication"** — Erythromycin is preferred over penicillin for diphtheria because it better eliminates the carrier state. [cite: Nelson's Textbook of Pediatrics 21e; Park's Textbook of Preventive & Social Medicine 26e Ch 8; IAP Guidelines]