1. Clinical Overview
Dapsone is a synthetic sulfone antibacterial and anti-inflammatory agent, primarily used for the treatment of leprosy (Hansen's disease) and dermatitis herpetiformis. It acts as a competitive antagonist of para-aminobenzoic acid (PABA) and inhibits bacterial folate synthesis. In the Indian context, it is a cornerstone of the National Leprosy Eradication Programme (NLEP) as part of Multi-Drug Therapy (MDT).
| Onset | Duration | Bioavailability |
|---|---|---|
| Clinical improvement in dermatitis herpetiformis is typically seen within 24-48 hours. For leprosy, bactericidal effects begin within hours, but clinical response may take several weeks. | Approximately 24-30 hours, supporting once-daily dosing. | 70-80% following oral administration. |
2. Mechanism of Action
Dapsone's primary mechanism is bacteriostatic against Mycobacterium leprae. It is a structural analogue of PABA and competitively inhibits dihydropteroate synthase (DHPS), an enzyme in the bacterial folate synthesis pathway. This depletes tetrahydrofolate, essential for DNA synthesis. Its anti-inflammatory effect in dermatological conditions is mediated by inhibition of neutrophil myeloperoxidase and chemotaxis, and scavenging of reactive oxygen species.
3. Indications & Uses
- Leprosy (all forms, as part of Multi-Drug Therapy - MDT)
- Dermatitis Herpetiformis (maintenance therapy)
4. Dosage & Administration
Adult Dosage: Leprosy (MDT): 100 mg once daily. Dermatitis Herpetiformis: Start 50 mg daily, titrate to response (usual range 50-300 mg daily). PCP Prophylaxis: 100 mg daily.
Administration: Administer orally with or without food. Taking with food may reduce GI upset. Tablet should be swallowed whole with a full glass of water. For leprosy MDT, dapsone is taken concurrently with rifampicin and clofazimine as per NLEP guidelines.
5. Side Effects
Common side effects may include:
- Dose-related hemolytic anemia (mild to moderate)
- Methemoglobinemia (cyanosis, headache, fatigue)
- Nausea, vomiting, anorexia
- Headache, dizziness
- Mild skin rash
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Rifampicin | Increases metabolism of dapsone, reducing its plasma levels and half-life. Critical in MDT; doses are adjusted accordingly. | Major |
| Probenecid | Decreases renal excretion of dapsone, increasing its plasma levels and risk of toxicity. | Major |
| Trimethoprim | Synergistic antifolate effect; dramatically increases risk of hematological toxicity (agranulocytosis, megaloblastic anemia). | Contraindicated |
| Primaquine, Chloroquine | Increased risk of hemolytic anemia and methemoglobinemia. | Major |
| Didanosine | Reduced absorption of dapsone if taken concurrently. Separate administration by at least 2 hours. | Moderate |
| Methotrexate | Increased risk of pancytopenia due to combined antifolate effect. | Major |
| Folic acid antagonists (e.g., Pyrimethamine) | Increased hematological toxicity. | Major |
| Amitriptyline, Clozapine | Increased risk of agranulocytosis. | Moderate |
7. Patient Counselling
- DO take the medication exactly as prescribed, even if you feel well.
- DO report for regular blood tests (CBC, LFT) as advised by your doctor.
- DO inform all your doctors and your dentist that you are taking dapsone.
- DO use sun protection (sunscreen, protective clothing) as dapsone may increase sun sensitivity.
- DONT stop taking the medication suddenly without consulting your doctor, especially for leprosy.
- DONT take any other medicines, including over-the-counter drugs or herbal supplements, without checking with your doctor or pharmacist.
8. Toxicology & Storage
Overdose: Severe nausea, vomiting, hyperexcitability, seizures, metabolic acidosis. The hallmark is severe methemoglobinemia (cyanosis, chocolate-brown blood, dyspnea, tachycardia, headache, fatigue, coma) and acute hemolytic anemia.
Storage: Store below 30°C, in a cool, dry place, protected from light. Keep the container tightly closed. Keep out of reach of children.