Antileprotic Drugs

Classification

Dapsone, rifampicin(mechanism/SE = Antitubercular Drugs, shared across both diseases), clofazimine — 3 drugs of standard MDT, combined for IDENTICAL resistance-prevention rationale as TB(large bacterial burden, real spontaneous resistance risk to any single agent).

Mechanism

Dapsone: sulfone, PABA analogue, competitive dihydropteroate synthase inhibition — IDENTICAL target/logic as sulfonamides(Sulfonamides topic), applied to M. leprae. Bacteriostatic.

Clofazimine: mechanism not fully elucidated — thought to bind mycobacterial DNA + generate ROS(redox-cycling) → bactericidal. + genuine independent ANTI-INFLAMMATORY property(helps manage reactional states below).

Rifampicin: most rapidly/potently bactericidal of the 3(identical RNA polymerase mechanism as TB) → allows short-duration MDT to render patient non-infectious quickly(same role as TB intensive phase).

MDT Regimen

Paucibacillary(tuberculoid, low bacterial load): rifampicin+dapsone, 6 months. Multibacillary(lepromatous, high bacterial load): rifampicin+dapsone+clofazimine, 12 months. Extra drug+longer duration = DIRECTLY reflects larger burden→higher absolute resistant-mutant risk — same population-size logic as TB regimen intensity.

Adverse Effects

Dapsone: haemolysis in G6PD deficiency(oxidant stressor — IDENTICAL underlying vulnerability as sulfonamide-class, not a separate fact) → screen G6PD before starting. Methaemoglobinaemia(related oxidant property). Dapsone hypersensitivity syndrome — SPECIFIC severe/potentially fatal(fever, rash, hepatitis, lymphadenopathy), typically 2-6wk after starting — named syndrome, not generic “drug allergy.”

Clofazimine: reddish-brown to blue-black skin discolouration — most distinctive, near-universal with prolonged use(skin/fat deposition), REVERSIBLE over months after stopping but major ADHERENCE issue(visible, stigmatizing — genuine public-health consideration given leprosy’s own social stigma). GI effects(abdominal pain, crystal deposition in gut wall/mesenteric nodes at high cumulative dose).

Rifampicin: as Antitubercular Drugs(hepatotoxicity, CYP450 induction, harmless red-orange fluid discolouration).

Leprosy Reactional States (specific complication, NOT paralleled in TB)

Immunologically-mediated inflammatory episodes, before/during/after treatment — antileprotic drugs typically CONTINUED unchanged through a reaction(reaction = immune response to existing bacterial antigen, NOT treatment failure).

Type 1(reversal reaction): delayed-type hypersensitivity → acute inflammation of existing lesions + NERVE involvement, risk of RAPID PERMANENT nerve damage if not promptly treated → corticosteroids, priority = urgent nerve function preservation.

Type 2(ENL — erythema nodosum leprosum): immune COMPLEX-mediated, specifically in MULTIBACILLARY disease → painful subcutaneous nodules+fever+systemic symptoms. THALIDOMIDE = specifically/distinctively effective(immunomodulatory/anti-TNF-α — famous non-teratogenicity use of this otherwise-teratogenic drug). Corticosteroids = alternative if thalidomide unavailable/CI(esp women of childbearing potential — thalidomide’s own severe teratogenic risk = genuine clinical tension in same patient population).

Clinical Relevance

Dapsone = direct extension of sulfonamide antifolate principle; reactional-state management = genuinely SEPARATE concern from antimicrobial regimen. This topic ISN’T just “leprosy’s TB” — recognize where TB parallel genuinely holds(multidrug rationale, rifampicin’s shared role) vs where leprosy specifically DIVERGES(reactional states, dapsone’s distinct target vs isoniazid/pyrazinamide) — that’s the actual exam distinction.

Classification

Dapsone, rifampicin (mechanism/adverse effects covered fully under Antitubercular Drugs, shared drug across both diseases), clofazimine — the three drugs of standard multidrug therapy (MDT) for leprosy, combined for the identical resistance-prevention rationale already established for tuberculosis under Antitubercular Drugs, given a comparably large bacterial burden and comparably real risk of spontaneous resistance to any single agent.

Mechanism of Action

Dapsone: a sulfone, mechanistically analogous to sulfonamides — a structural PABA analogue competitively inhibiting dihydropteroate synthase in the bacterial folate synthesis pathway, the identical target and logic already described for sulfonamides under Sulfonamides and Cotrimoxazole, here applied to Mycobacterium leprae rather than a typical bacterium. Bacteriostatic against M. leprae.

Clofazimine: mechanism is not fully elucidated, but is thought to bind mycobacterial DNA and generate reactive oxygen species (via a redox-cycling mechanism), producing bactericidal activity against M. leprae, alongside a genuinely useful independent anti-inflammatory property that specifically helps manage the leprosy reactional states described below.

Rifampicin: the most rapidly and potently bactericidal of the three against M. leprae (identical RNA polymerase-inhibiting mechanism as in tuberculosis) — its inclusion is what allows relatively short-duration MDT regimens to render a patient non-infectious quickly, analogous to its role in the intensive phase of TB therapy.

MDT Regimen Structure

Paucibacillary leprosy (tuberculoid form, low bacterial load, fewer skin lesions): rifampicin + dapsone, for 6 months. Multibacillary leprosy (lepromatous form, high bacterial load, more extensive skin/nerve involvement): rifampicin + dapsone + clofazimine, for 12 months — the added third drug and longer duration directly reflect the larger bacterial burden and correspondingly higher absolute risk of spontaneous resistant mutants requiring more thorough coverage, the same population-size-driven logic already established for TB regimen intensity.

Adverse Effects

Dapsone: haemolysis in G6PD deficiency (dapsone is an oxidant stressor, mechanistically identical to the sulfonamide-class oxidant-haemolysis risk already covered — worth recognizing as the same underlying vulnerability rather than a separate fact specific to dapsone) — screening for G6PD deficiency before starting dapsone is standard practice given this risk. Methaemoglobinaemia (a further consequence of its oxidant properties, distinct from but related to the haemolysis risk). Dapsone hypersensitivity syndrome — a specific, severe, potentially fatal reaction (fever, rash, hepatitis, lymphadenopathy) typically occurring 2–6 weeks after starting therapy, a genuinely important, specifically-named syndrome rather than generic “drug allergy,” worth learning as its own entity.

Clofazimine: reddish-brown to blue-black skin discolouration — the drug’s most distinctive, near-universal adverse effect with prolonged use, related to drug deposition in skin and fat, generally reversible over months after stopping therapy but a significant cause of poor treatment adherence given its visible, stigmatizing nature (a genuinely important public-health/adherence consideration in leprosy treatment specifically, given the disease’s own historical social stigma). GI effects (abdominal pain, occasionally severe, related to clofazimine crystal deposition in the intestinal wall/mesenteric lymph nodes at high cumulative doses).

Rifampicin: as covered under Antitubercular Drugs (hepatotoxicity, CYP450 induction, harmless red-orange fluid discolouration).

Leprosy Reactional States — A Specific, Frequently-Tested Complication

Leprosy treatment carries a distinctive complication not paralleled in tuberculosis therapy: reactional states, immunologically-mediated inflammatory episodes that can occur before, during, or after antileprotic treatment, requiring separate management from the antimicrobial regimen itself (the antileprotic drugs are typically continued unchanged through a reaction, since the reaction reflects immune response to already-present bacterial antigen, not treatment failure):

Type 1 reaction (reversal reaction): a delayed-type hypersensitivity response, causing acute inflammation of existing skin lesions and, critically, nerve involvement with risk of rapid, permanent nerve damage if not promptly treated — managed with corticosteroids, the priority being urgent nerve function preservation.
Type 2 reaction (erythema nodosum leprosum, ENL): an immune complex-mediated reaction, occurring specifically in multibacillary/lepromatous disease, presenting with painful subcutaneous nodules, fever, and systemic symptoms — thalidomide is specifically and distinctively effective for ENL (a well-known, frequently-examined use of a drug otherwise defined by its teratogenicity, given thalidomide’s immunomodulatory/anti-TNF-α property), with corticosteroids as an alternative where thalidomide is unavailable or contraindicated (notably, in women of childbearing potential, given thalidomide’s own severe teratogenic risk — a genuine clinical tension between two significant considerations in the same patient population).

Clinical Relevance

Dapsone’s mechanism as a direct extension of the sulfonamide antifolate principle, and the reactional-state management existing as a genuinely separate concern from the antimicrobial regimen itself, are the two organizing ideas that make this topic more than “leprosy’s version of TB therapy” — recognizing where the parallel with tuberculosis genuinely holds (multidrug rationale, rifampicin’s shared role) and where leprosy specifically diverges (reactional states, dapsone’s distinct target relative to isoniazid/pyrazinamide) is what the exam is actually testing.

Paucibacillary vs multibacillary MDT regimen comparison (drugs and duration) linked to bacterial burden.
Type 1 vs Type 2 (ENL) leprosy reactional states compared by mechanism, presentation, and specific treatment.