A 28-year-old woman with tuberculoid leprosy (single lesion, <5 lesions, low bacterial index) is being initiated on multidrug therapy. Which drug is the preferred first-line agent for paucibacillary leprosy?

Explanation

## Classification: Paucibacillary vs Lepromatous Leprosy **Key Point:** Tuberculoid leprosy (TT) is a **paucibacillary form** — characterized by <5 lesions, high cell-mediated immunity, low or absent acid-fast bacilli (AFB) on slit-skin smear, and good prognosis. ## WHO-MDT for Paucibacillary Leprosy (6-Month Regimen) Paucibacillary leprosy requires a **shorter, 6-month MDT** compared to the 12-month regimen for lepromatous disease. ### MDT-PB Composition | Component | Drug | Dose | Frequency | Role | |-----------|------|------|-----------|------| | **Backbone** | **Rifampicin** | 600 mg | Monthly supervised | Bactericidal; first-line | | **Second agent** | **Dapsone** | 100 mg | Daily unsupervised | Bacteriostatic | | **Duration** | — | — | 6 months | Shorter than MDT-LL | **High-Yield:** Rifampicin is the **first-line drug in ALL leprosy regimens** — both paucibacillary (TB, BT) and lepromatous (BL, LL). The difference is in the **duration and number of additional drugs**, not in the backbone. ## Why Rifampicin is the Drug of Choice in Paucibacillary Leprosy 1. **Bactericidal** — directly kills *M. leprae* 2. **Rapid efficacy** — renders patient non-infectious within 2 weeks 3. **Essential in all MDT** — no alternative backbone exists 4. **Prevents relapse** — combination therapy prevents resistance **Clinical Pearl:** In paucibacillary leprosy, the bacterial load is already low, so a 6-month regimen with two drugs (rifampicin + dapsone) is sufficient, whereas lepromatous disease requires 12 months with three drugs (rifampicin + dapsone + clofazimine). **Mnemonic: MDT Backbone = RIF** (Rifampicin is the **I**nvariant, **F**irst-line drug in all forms)