Dapsone

Dapsone is a synthetic sulfone antibiotic medication with a well-established history in dermatology and infectious disease. Its primary mechanism of action involves inhibition of bacterial folate synthesis and potent anti-inflammatory effects, particularly through the suppression of neutrophil-mediated responses. This dual-action profile makes it a cornerstone therapy for a range of difficult-to-treat inflammatory and infectious skin disorders, offering a critical option for patients where conventional treatments have failed or are unsuitable.

Features

• Active Ingredient: Dapsone
• Drug Class: Sulfone antibiotic
• Available Forms: Oral tablets (25 mg, 100 mg), topical gel (7.5%)
• Mechanism of Action: Competitive antagonist of para-aminobenzoic acid (PABA), inhibiting dihydrofolic acid synthesis in susceptible bacteria; also inhibits neutrophil migration and myeloperoxidase-H2O2-halide-mediated cytotoxic system
• Bioavailability: Approximately 70-80% after oral administration
• Protein Binding: 70-90%
• Metabolism: Hepatic via N-acetylation (polymorphic) and N-hydroxylation
• Half-life: 20-30 hours (range 10-50 hours)
• Excretion: Primarily renal (unchanged drug and metabolites)

Benefits

• Provides targeted anti-inflammatory and antibacterial action for complex dermatoses
• Offers a well-tolerated systemic option for patients unresponsive to topical therapies
• Demonstrates rapid clinical response in many inflammatory conditions, often within 4-8 weeks
• Serves as a steroid-sparing agent, reducing long-term corticosteroid exposure
• Effective for both infectious and immune-mediated conditions through dual mechanisms
• Available in multiple formulations allowing for tailored treatment approaches

Common use

Dapsone is FDA-approved for the treatment of dermatitis herpetiformis and leprosy (Hansen’s disease). Its off-label uses are extensive in dermatology, particularly for various neutrophilic dermatoses. It is commonly prescribed for acne vulgaris, especially inflammatory forms resistant to conventional antibiotics. Other frequent applications include subcorneal pustular dermatosis, linear IgA bullous dermatosis, pemphigus vulgaris and foliaceus, and bullous lupus erythematosus. In infectious disease contexts beyond leprosy, it finds use in Pneumocystis jirovecii pneumonia prophylaxis in immunocompromised patients, particularly those with HIV/AIDS who cannot tolerate trimethoprim-sulfamethoxazole.

Dosage and direction

For dermatitis herpetiformis: Adults typically start at 50 mg daily, increasing to 300 mg daily or higher until symptom control is achieved, then tapering to the lowest effective maintenance dose (often 25-100 mg daily). For leprosy: 100 mg daily in combination with other antimycobacterial agents. For acne vulgaris: 50-100 mg daily, often starting lower to assess tolerance. Topical dapsone gel is applied twice daily to affected areas. Administration with food may minimize gastrointestinal upset. Regular monitoring of complete blood count and liver function is mandatory during therapy. Dosage adjustments are necessary in renal impairment.

Precautions

Hemolytic anemia is a significant concern, particularly in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency, which must be ruled out before initiation. Methemoglobinemia occurs frequently at higher doses and requires monitoring for cyanosis, dyspnea, fatigue, and tachycardia. Peripheral neuropathy, usually motor, may occur with long-term use. Regular laboratory monitoring including CBC, liver function tests, and methemoglobin levels is essential. Use with caution in patients with cardiovascular or pulmonary disease due to reduced oxygen-carrying capacity. Pregnancy Category C: use only if potential benefit justifies potential risk to fetus.

Contraindications

Absolute contraindications include known hypersensitivity to dapsone or other sulfone drugs, and demonstrated G6PD deficiency (due to risk of severe hemolysis). Relative contraindications include severe anemia, methemoglobin reductase deficiency, hepatic impairment, and concomitant use with drugs that cause hemolysis or suppress bone marrow function. The topical formulation is contraindicated in patients with known hypersensitivity to any component of the formulation.

Possible side effect

Common adverse effects include hemolytic anemia (dose-related), methemoglobinemia (dose-related), nausea, vomiting, abdominal pain, headache, dizziness, and blurred vision. Less frequent effects include rash, photosensitivity, fever, insomnia, and peripheral neuropathy. Serious but rare adverse effects include agranulocytosis, drug reaction with eosinophilia and systemic symptoms (DRESS), hepatitis, and exfoliative dermatitis. The topical formulation may cause local dryness, erythema, and oiliness.

Drug interaction

Dapsone interacts significantly with probenecid (increases dapsone levels), trimethoprim (increases both drugs’ levels and toxicity risk), rifampin (decreases dapsone levels), and didanosine (reduces dapsone absorption). Concurrent use with other hemolytic agents increases hematologic toxicity. Drugs that induce cytochrome P450 enzymes may decrease dapsone efficacy, while inhibitors may increase toxicity. Antacids may reduce absorption. Dapsone may decrease the efficacy of oral contraceptives.

Missed dose

If a dose is missed, it should be taken as soon as remembered unless it is nearly time for the next dose. Do not double the dose to make up for a missed one. Consistent daily administration is important for maintaining therapeutic levels. If multiple doses are missed, contact the prescribing physician for guidance on resumption, as re-titration may be necessary.

Overdose

Symptoms of overdose include nausea, vomiting, hyperexcitability, seizures, and severe methemoglobinemia (evidenced by cyanosis, chocolate-brown colored blood, respiratory depression, and coma). Management is supportive with gastric lavage if presented early, methylene blue for methemoglobinemia (1-2 mg/kg IV slowly over 5 minutes, repeat as needed), and seizure control. Hemodialysis is not effective due to high protein binding. Activated charcoal may be administered.

Storage

Store at controlled room temperature (20-25°C or 68-77°F), protected from light and moisture. Keep in original container tightly closed. Do not freeze. Keep out of reach of children and pets. Properly discard any expired medication. Do not transfer to other containers as this may affect stability.

Disclaimer

This information is for educational purposes only and does not constitute medical advice. Dapsone is a prescription medication that should only be used under the supervision of a qualified healthcare professional. The prescribing physician will determine the appropriate dosage and monitor for potential adverse effects. Patients should not initiate, discontinue, or change their dosage without medical consultation. Individual responses to medication may vary.

Reviews

Clinical studies demonstrate dapsone’s efficacy across multiple indications. In dermatitis herpetiformis, it produces complete symptom control in approximately 90% of patients within 1-2 days of initiation. For inflammatory acne, studies show 40-50% reduction in inflammatory lesions at 12 weeks. The topical formulation shows significant efficacy with favorable tolerability. Long-term experience supports its safety profile with appropriate monitoring. Many dermatologists consider it an invaluable tool for treatment-resistant cases, though note the importance of pretreatment screening and ongoing monitoring.