A 32-year-old man from rural Maharashtra presents with a 3-month history of cough, fever, and night sweats. Chest X-ray shows cavitary lesions in the right upper lobe. Sputum smear microscopy is positive for acid-fast bacilli. He has no prior TB treatment history and normal renal and hepatic function. What is the drug of choice as the backbone of his initial intensive phase regimen?

Explanation

## First-Line Anti-TB Drugs: Intensive Phase Backbone **Key Point:** Rifampicin is the most potent bactericidal anti-TB agent and forms the backbone of all standard TB regimens, both in the intensive and continuation phases. ### Role of Rifampicin in TB Treatment Rifampicin is the single most important drug in TB therapy because it: - Has the **highest bactericidal activity** against *Mycobacterium tuberculosis* - Kills both intracellular and extracellular organisms - Reduces bacterial load most rapidly in the first 2 weeks - Is present in **all standard TB regimens** (2HRZE/4HR, 2HRZ/4HR) - Achieves excellent lung penetration ### Standard Intensive Phase Regimen (2 months) | Drug | Role | Dosing | |------|------|--------| | **Isoniazid (H)** | Bactericidal; sterilizes lesions | 5 mg/kg daily | | **Rifampicin (R)** | Most potent; backbone drug | 10 mg/kg daily | | **Pyrazinamide (Z)** | Bactericidal; shortens duration | 25 mg/kg daily | | **Ethambutol (E)** | Bacteriostatic; prevents resistance | 15 mg/kg daily | **High-Yield:** The 4-drug combination (HRZE) for 2 months followed by 2-drug continuation (HR) for 4 months is the standard regimen for drug-susceptible TB. Rifampicin is **never omitted** from any TB regimen. ### Why Rifampicin Is the Backbone 1. **Fastest bacterial kill rate** — reduces viable organisms by 99% in first 2 weeks 2. **Prevents drug resistance** — when used with other agents 3. **Sterilizes cavitary lesions** — kills organisms in acidic, hypoxic environments 4. **Mandatory in all regimens** — WHO and Indian TB guidelines mandate rifampicin in every TB patient **Clinical Pearl:** Rifampicin's orange-red discoloration of body secretions (urine, tears, sweat) is a useful compliance marker and reassures patients of drug absorption. **Mnemonic:** **HRZE** = **H**eavy hitter (Isoniazid) + **R**apid killer (Rifampicin) + **Z**ero resistance (Pyrazinamide) + **E**arly addition (Ethambutol).