Antileprotic Drugs (Leprosy)

Antileprotic Drugs (Leprosy)

1. Definition, disease background & historical evolution

• Leprosy (Hansen disease) is a chronic granulomatous infection caused by Mycobacterium leprae, primarily affecting skin, mucous membranes and peripheral nerves; it carries a heavy social stigma but is now entirely curable with effective antileprotic drugs — though deformities/defects already incurred may not reverse (KDT 8e Ch.57, pp.831, 834).
• M. leprae was discovered by Armauer Hansen in 1873 — hence "Hansen disease" (G&G 14e Ch.65, p.1281).
• Key biological features of M. leprae that shape therapy (G&G 14e Ch.65, p.1281):
  • Obligate intracellular pathogen with a very long doubling time (~14 days) → mandates prolonged, months-to-years therapy.
  • Has undergone reductive (genome-decay) evolution — radically downsized genome (Cole et al., 2001).
  • Cannot be cultured in vitro / on synthetic media — an impediment to research and clinical identification; drug evaluation historically relied on the mouse footpad model of injected bacilli (G&G 14e Ch.65, p.1281; Katzung 16e Ch.47, p.895).
• Mycobacterial therapeutic barriers (apply across the genus, relevant to penetration): lipid-rich (>60% mycolic-acid) waxy cell wall, abundant efflux pumps, and intracellular + avascular tissue localisation of bacilli (G&G 14e Ch.65, p.1267).
• Historical drug evolution (KDT 8e Ch.57, p.831):
  • Chaulmoogra oil — weak antileprotic, used in Indian medicine for centuries.
  • Dapsone (the parent sulfone) — identified shortly after sulfonamide antibacterial activity was demonstrated; sheet-anchor of leprosy treatment since the 1940s. No other sulfone could excel dapsone; all others are now obsolete.
  • Clofazimine — inducted in the early 1960s as a useful adjunct (first licensed for leprosy 1969 — G&G 14e Ch.65, p.1271).
  • Rifampin — developed for TB, soon found to be a rapidly acting cidal drug for M. leprae.
  • Newer agents — good antileprotic activity later detected in some fluoroquinolones, macrolides (clarithromycin) and minocycline.