Generic Dapsone ( Diaminodiphenyl sulfone )

Buy Generic Dapsone (Diaminodiphenyl sulfone) without prescription in Canada

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Dapsone is an antibacterial and anti‑inflammatory sulfone drug used primarily for the treatment of leprosy (Hansen’s disease) in combination with other agents, for dermatitis herpetiformis (a chronic blistering skin condition linked to gluten sensitivity), and for the prevention and treatment of Pneumocystis jirovecii pneumonia (PCP) in immunocompromised patients. It works by inhibiting the synthesis of dihydrofolic acid in susceptible organisms through competition with para‑aminobenzoic acid (PABA), thereby disrupting folate metabolism and nucleic acid synthesis; its anti‑inflammatory effects in dermatitis herpetiformis are less well understood but involve suppression of neutrophil migration and myeloperoxidase activity.

Usual adult dose: For leprosy, the recommended dose is 100 mg taken orally once daily in combination with rifampicin and clofazimine for 12 months; for dermatitis herpetiformis, the starting dose is usually 50 mg daily, titrated upward to a maintenance range of 50‑300 mg daily (often 100 mg daily) as tolerated. For PCP prophylaxis, 100 mg once daily or 50 mg twice daily is used, either alone or with pyrimethamine and leucovorin. The tablet is available in 100 mg strength, supplied in institutional bulk packs of 1000 capsules or tablets for public health programs and long‑term therapy, although smaller pharmacy bottles are also available. Doses should be taken with food to reduce gastrointestinal irritation.

Dosage form: Oral tablets or capsules, 100 mg. Also available in 25 mg and 50 mg strengths in some markets. The 1000‑capsule bulk presentation is typical for leprosy control programs and long‑term dermatitis herpetiformis management.

Onset of action: In leprosy, clinical improvement is gradual; cutaneous lesions begin to resolve within 3‑6 months of starting multidrug therapy. In dermatitis herpetiformis, pruritus and new blister formation may be controlled within days to weeks of achieving the effective dose. For PCP prophylaxis, the protective effect begins after the first week of daily intake.

Duration of action: The elimination half‑life of dapsone is approximately 20‑30 hours, supporting once‑daily dosing. The clinical effect persists as long as the drug is taken regularly; relapse of symptoms in dermatitis herpetiformis occurs within days of discontinuation.

Alcohol recommendation: Alcohol consumption should be limited or avoided during treatment with Dapsone. Alcohol may increase the risk of liver toxicity and can exacerbate gastrointestinal side effects. Heavy alcohol intake may also reduce the efficacy of dapsone and increase the likelihood of adverse haematological reactions.

Most common side effects: Haemolytic anaemia (dose‑related, especially in patients with glucose‑6‑phosphate dehydrogenase [G6PD] deficiency), methaemoglobinaemia (which can cause cyanosis and fatigue), nausea, vomiting, headache, and peripheral neuropathy. More serious adverse reactions include agranulocytosis, aplastic anaemia, peripheral motor neuropathy, and dapsone hypersensitivity syndrome (DRESS), which can be life‑threatening and typically develops 3‑6 weeks after starting therapy. All patients should be screened for G6PD deficiency before starting dapsone, and regular monitoring of complete blood counts is mandatory.

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General Information about Dapsone (Diaminodiphenyl sulfone)

• INN (International Nonproprietary Name): Dapsone (4,4′‑diaminodiphenyl sulfone)
• Brand names available in Canada: Dapsone is available under its generic name; brand‑name products are not marketed, but it is supplied by Jacobus Pharmaceutical Company (USA) and various generic manufacturers. It is available in 100 mg tablets and as a topical gel (Aczone® 5% for acne, which is not the indication here). For leprosy and dermatitis herpetiformis, the oral tablet is the standard form.
• ATC code: J04BA02 (dapsone; drugs for treatment of lepra).
• Dosage forms and strengths: Oral tablets: 25 mg, 50 mg, and 100 mg. The 100 mg tablet is the most commonly prescribed strength. Institutional bulk packs of 1000 tablets/capsules are available for public health programs.
• Manufacturers in Canada: Jacobus Pharmaceutical Company is a primary supplier of dapsone tablets to the Canadian market. Various generic manufacturers also produce dapsone. The product is distributed through pharmacies and institutional channels.
• Registration status in Canada: Approved by Health Canada for the indications of leprosy, dermatitis herpetiformis, and PCP prophylaxis. DINs for dapsone 100 mg tablets exist (e.g., 02180635).
• OTC / Rx classification: Prescription only (Rx). Schedule I drug under the Controlled Drugs and Substances Act. A valid prescription from a licensed Canadian healthcare professional is required.

Mechanism of Action and Pharmacology

Dapsone is a structural analogue of para‑aminobenzoic acid (PABA) and acts as a competitive inhibitor of dihydropteroate synthetase in the folate biosynthetic pathway of bacteria and protozoa, thereby blocking the synthesis of dihydrofolic acid and ultimately DNA and RNA production. This action is bacteriostatic against Mycobacterium leprae and is the basis for its use in leprosy. For Pneumocystis jirovecii, the same mechanism inhibits folate synthesis of the organism. In dermatitis herpetiformis, the exact mechanism is unknown; dapsone does not affect the gluten‑sensitive enteropathy itself but suppresses the cutaneous inflammatory response, possibly by inhibiting neutrophil adherence, migration, and release of lysosomal enzymes (myeloperoxidase) and reactive oxygen species.

After oral administration, dapsone is rapidly and almost completely absorbed, with peak plasma concentrations occurring within 2‑8 hours. The drug is extensively metabolised in the liver by acetylation (N‑acetylation) and N‑hydroxylation, the latter producing the toxic metabolite dapsone hydroxylamine, which is responsible for haemolysis and methaemoglobinaemia. Dapsone exhibits significant enterohepatic recycling. The elimination half‑life of dapsone ranges from 20‑30 hours, and it is highly protein‑bound (70‑90%). The metabolites are excreted in the urine. In patients with G6PD deficiency, the reduced ability to detoxify oxidant stress leads to severe haemolysis and anaemia. Therefore, G6PD screening is essential before starting therapy, and patients should be monitored for signs of haemolysis. The drug is also a weak inhibitor of CYP2C9 and CYP3A4, though clinically significant interactions are limited.

Indications

• Leprosy (Hansen’s disease): As part of a multidrug regimen (with rifampicin and clofazimine) for the treatment of multibacillary and paucibacillary leprosy. Dapsone alone is not recommended due to the risk of resistance.
• Dermatitis herpetiformis: For the treatment of the cutaneous manifestations of dermatitis herpetiformis, a chronic, intensely pruritic blistering skin disease associated with gluten sensitivity. Dapsone controls the skin lesions but does not treat the underlying enteropathy; a gluten‑free diet is the definitive treatment.
• Pneumocystis jirovecii pneumonia (PCP) prophylaxis: As an alternative to trimethoprim‑sulfamethoxazole in immunocompromised patients (e.g., HIV/AIDS, transplant recipients) who are intolerant of first‑line agents.
• Off‑label uses: Prophylaxis of toxoplasmosis, treatment of linear IgA bullous dermatosis, and other neutrophilic dermatoses.

Important Warnings and Precautions

At‑risk groups

• Pregnancy: Dapsone crosses the placenta. It should be used during pregnancy only if the potential benefit clearly justifies the potential risk to the foetus. It is considered acceptable for use during pregnancy when needed for leprosy or dermatitis herpetiformis unresponsive to other measures, but near‑term use may cause neonatal haemolysis and methaemoglobinaemia. Pregnant women should receive folic acid supplementation, and the newborn should be monitored.
• Breastfeeding: Dapsone is excreted in human breast milk in amounts that are probably safe for the nursing infant; haemolytic anaemia has been reported in some breastfed infants, particularly those with G6PD deficiency. Breastfeeding is not recommended unless the mother’s clinical need is compelling, and the infant should be observed for signs of haemolysis or jaundice. An alternative feeding method may be considered.
• Paediatrics: Safety and efficacy have been established for leprosy and dermatitis herpetiformis in children; doses are weight‑based (1‑2 mg/kg/day). Monitoring for haematological effects is especially important in paediatric patients.
• Elderly: No specific dose adjustment is required, but elderly patients may be more susceptible to haemolysis, methaemoglobinaemia, and peripheral neuropathy. Lower starting doses (e.g., 50 mg daily) and careful monitoring are recommended.
• G6PD deficiency: Patients with glucose‑6‑phosphate dehydrogenase deficiency are at high risk of severe haemolytic anaemia when taking dapsone. All patients should be screened for G6PD deficiency before starting therapy. If the test is positive, dapsone should be used only if absolutely necessary and with extreme caution, at the lowest effective dose, with frequent monitoring of haemoglobin and reticulocyte count.
• Haemolytic anaemia and methaemoglobinaemia: Dose‑related haemolysis and methaemoglobinaemia occur to some degree in all patients. Significant anaemia may develop within weeks, especially at doses above 200 mg/day. Patients should have a complete blood count, reticulocyte count, and methaemoglobin level measured at baseline and regularly during therapy (weekly for the first month, then every 2‑4 weeks). If haemoglobin falls below 8‑10 g/dL or significant symptoms develop, the dose must be reduced or the drug discontinued. Methaemoglobinaemia typically presents with cyanosis, headache, and fatigue; levels above 15‑20% require treatment with methylene blue.
• Dapsone hypersensitivity syndrome (DRESS): A potentially fatal syndrome characterised by fever, rash, eosinophilia, lymphadenopathy, and multi‑organ involvement (hepatitis, nephritis, pneumonitis, myocarditis) typically occurs 3‑6 weeks after starting treatment. The drug must be discontinued immediately at the first sign of hypersensitivity, and supportive care should be provided. Rechallenge is contraindicated.
• Peripheral neuropathy: Motor and sensory neuropathy, predominantly axonal, has been reported with dapsone, often after prolonged use. Early symptoms include muscle weakness and wasting in the hands and feet. If neuropathy develops, dapsone should be discontinued, as the nerve damage may be irreversible.
• Agranulocytosis and aplastic anaemia: Rare but life‑threatening bone marrow suppression can occur. Any significant drop in white blood cell or platelet count requires immediate discontinuation and haematological evaluation.
• Allergy: Do not take Dapsone if you have a known hypersensitivity to dapsone, other sulfones, or any excipient in the formulation. Cross‑sensitivity with sulfonamide antibiotics may occur.

Driving and alcohol

Dapsone may cause dizziness, headache, and fatigue, especially at the start of therapy or with high doses, which could impair the ability to drive or operate machinery. Patients should be cautious until they know how the medication affects them. Alcohol should be limited or avoided because it can increase the risk of liver toxicity, worsen gastrointestinal side effects, and may contribute to methaemoglobinaemia. Heavy alcohol consumption can also interfere with medication adherence.

Dosage Instructions

• Leprosy (adults): 100 mg once daily, in combination with rifampicin 600 mg once monthly (supervised) and clofazimine 50 mg daily plus 300 mg once monthly. Treatment is continued for 12 months (multibacillary) or 6 months (paucibacillary) according to WHO guidelines. The 100 mg tablet is standard.
• Dermatitis herpetiformis (adults): Start with 50 mg daily; increase gradually to a maintenance dose of 50‑300 mg daily, usually 100 mg daily, according to clinical response and tolerability. The lowest effective dose should be used. A gluten‑free diet reduces the need for dapsone over time.
• PCP prophylaxis (adults): 100 mg once daily or 50 mg twice daily, alone or in combination with pyrimethamine 50 mg plus leucovorin 25 mg once weekly (for toxoplasmosis prophylaxis).
• Administration: The tablet should be swallowed whole with a glass of water and should be taken with food or a meal to reduce stomach upset. For patients with difficulty swallowing, the tablet may be crushed and mixed with food; however, bitter taste may be an issue. Adherence to the daily schedule is essential for efficacy. For leprosy, supervised monthly rifampicin is required; the patient must attend clinic appointments.
• Missed dose: If a dose is missed, take it as soon as remembered on the same day. If it is close to the time of the next dose, skip the missed dose and continue with the regular schedule. Do not double the dose.

Side Effects and Contraindications

• Very common (≥ 10%): Haemolytic anaemia (dose‑dependent), methaemoglobinaemia, and nausea. Headache and fatigue are also common.
• Common (1‑10%): Vomiting, abdominal pain, anorexia, and rash. Peripheral neuropathy occurs less frequently but is a serious concern.
• Serious adverse reactions: Dapsone hypersensitivity syndrome (DRESS; mortality up to 10%), agranulocytosis, aplastic anaemia, severe haemolysis leading to anemia and hypoxia, and irreversible peripheral motor neuropathy.
• Contraindications: Known hypersensitivity to dapsone or other sulfones. Severe anaemia (Hb < 10 g/dL) unless due to the disease being treated. G6PD deficiency is a relative contraindication; if dapsone is essential, it must be used with extreme caution and close haematological monitoring. Concomitant use of didanosine and hydroxyurea is not recommended due to additive haemolytic risk.

Drug Interactions

• Rifampicin: Rifampicin increases the metabolism of dapsone, reducing its plasma levels by 7‑10 fold. Dapsone dose adjustment is not typically required when used in standard leprosy multidrug therapy because the clinical response is adequate. For other indications, if rifampicin is co‑administered, the dapsone dose may need to be increased, and monitoring of clinical response is advised.
• Trimethoprim and/or sulfamethoxazole: Additive haematological toxicity (bone marrow suppression, haemolysis) may occur; concomitant use is not recommended unless necessary, and enhanced monitoring is required.
• Didanosine and hydroxyurea: Additive haemolytic risk; concomitant use is contraindicated.
• Probenecid: Probenecid may reduce the renal excretion of dapsone metabolites, increasing the risk of toxicity. Use with caution and monitor for side effects.
• Pyrimethamine: Additive folate antagonism; leucovorin (folinic acid) supplementation is recommended to protect the bone marrow.
• CYP2C9 and CYP3A4 substrates: Dapsone is a weak inhibitor; clinical significance is limited but caution is advised when co‑administered with drugs that have a narrow therapeutic index (e.g., warfarin, phenytoin). Monitor INR for warfarin.

Practical Advice

• Administration: Take dapsone with food or after a meal to reduce stomach upset. Swallow the tablet whole with water. For dermatitis herpetiformis, a strict gluten‑free diet is essential for long‑term control and will reduce the need for dapsone over time; do not rely on medication alone. For leprosy, take all prescribed drugs exactly as directed and attend all scheduled clinic visits for supervised rifampicin doses and skin smears. Large institutional packs (1000 tablets) may be dispensed for long‑term therapy; store the excess tablets safely at home in a cool, dry place.
• Monitoring: Complete blood count (CBC), reticulocyte count, and methaemoglobin level should be checked at baseline and weekly for the first month, then every 2‑4 weeks for the first 6 months, and every 3‑6 months thereafter. Liver function tests (ALT, AST) should be monitored periodically. G6PD screening must be performed before starting therapy. Patients should be educated to report symptoms of haemolysis (dark urine, jaundice, shortness of breath, fatigue), methaemoglobinaemia (blue/grey discolouration of lips, nail beds, or skin), peripheral neuropathy (tingling, numbness, muscle weakness), and hypersensitivity (fever, rash, swollen glands).
• Storage: Store at room temperature (15‑30 °C) in a dry place, protected from light and moisture. Keep the container tightly closed. Keep out of the reach and sight of children. For the 1000‑tablet bulk pack, transfer a smaller supply to a labelled, child‑resistant container for daily use, and store the main supply in a secure, cool, dry location as directed by your pharmacist.
• Lifestyle: For dermatitis herpetiformis, adherence to a gluten‑free diet is critical; it may eventually allow a reduction or discontinuation of dapsone. Avoid alcohol to reduce the risk of liver toxicity and gastrointestinal upset. Do not stop dapsone abruptly without consulting your doctor, as a relapse of skin lesions or worsening of leprosy may occur. Inform all healthcare providers that you are taking dapsone, including dentists, surgeons, and pharmacists, especially if you require any medication that may affect blood counts or interact with dapsone.
• Missed dose: If you miss a dose, take it as soon as you remember on the same day with food. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not take a double dose.
• When to seek medical review: Contact your doctor immediately if you experience: signs of haemolysis (dark urine, yellowing of the skin or eyes, pale skin, severe fatigue or shortness of breath); signs of methaemoglobinaemia (bluish lips, tongue, or nail beds; headache; confusion); signs of infection (fever, sore throat, mouth ulcers, unusual bruising or bleeding — may indicate agranulocytosis); signs of peripheral neuropathy (weakness or numbness in hands or feet, difficulty walking); or signs of hypersensitivity (fever, rash, swollen lymph nodes, facial swelling). Seek emergency care for difficulty breathing, severe dizziness, or loss of consciousness.
• Disposal: Return unused or expired medication to a pharmacy for safe disposal. Do not flush down the toilet or discard in household waste.

Alternative Medications

• For leprosy (alternatives to dapsone): Clofazimine and rifampicin remain the cornerstone of therapy. In patients intolerant of dapsone, the WHO multibacillary regimen can be modified: rifampicin, clofazimine, and ofloxacin or minocycline may be used. For paucibacillary disease, rifampicin and clofazimine alone may be considered. Any change must be managed by a leprosy specialist.
• For dermatitis herpetiformis: Sulfapyridine is an alternative if dapsone is not tolerated, though it is less effective and has similar haematological risks. Topical corticosteroids and a strict gluten‑free diet are the mainstays; many patients can eventually discontinue dapsone with adequate dietary control.
• For PCP prophylaxis: Trimethoprim‑sulfamethoxazole (TMP‑SMX) is the first‑line agent, but alternatives for those intolerant include atovaquone, aerosolised pentamidine, or dapsone (the latter is second‑line). The choice depends on tolerance, allergy profile, and efficacy.
• For other neutrophilic dermatoses (linear IgA disease, etc.): Dapsone is first‑line, but alternatives such as sulfapyridine or colchicine may be tried under specialist supervision.

Clinical Efficacy

Dapsone has been a component of leprosy treatment since the 1940s and remains an essential drug in the WHO multidrug therapy regimen. When used in combination with rifampicin and clofazimine, it achieves high cure rates and prevents the development of dapsone resistance. In dermatitis herpetiformis, dapsone is dramatically effective: pruritus and blistering often resolve within 48‑72 hours of starting therapy, and the drug remains the standard of care for immediate symptom control. For PCP prophylaxis, dapsone has been shown to be as effective as TMP‑SMX in preventing Pneumocystis pneumonia, with a similar rate of breakthrough infections, though it may be less effective against toxoplasmosis unless combined with pyrimethamine. The major limitation of dapsone therapy is its haematological toxicity, particularly haemolytic anaemia and methaemoglobinaemia, which require careful monitoring. The development of the dapsone hypersensitivity syndrome (DRESS) is a life‑threatening complication that necessitates immediate discontinuation. Despite these risks, when used with appropriate screening and monitoring, dapsone remains a highly effective and cost‑efficient therapy for its approved indications, particularly in resource‑limited settings, and the 1000‑tablet institutional pack reflects its use in long‑term, large‑scale public health programs.

Important:

Dapsone is a prescription medication that must be used under the supervision of a qualified healthcare professional. It can cause life‑threatening adverse effects, including severe haemolytic anaemia, methaemoglobinaemia, agranulocytosis, and a potentially fatal hypersensitivity syndrome (DRESS). All patients must have a glucose‑6‑phosphate dehydrogenase (G6PD) deficiency test before starting treatment. Regular blood counts and methaemoglobin monitoring are mandatory throughout therapy. Do not take dapsone if you have severe anaemia or known G6PD deficiency unless specifically directed by your physician. If you experience symptoms such as dark urine, jaundice, severe fatigue, bluish discolouration of the lips or fingertips, fever, rash, swollen glands, or muscle weakness, stop the medication immediately and seek urgent medical attention. Dapsone must be taken with food and exactly as prescribed. This product is intended for the treatment of leprosy, dermatitis herpetiformis, or PCP prophylaxis and is not a cure for the underlying conditions without appropriate adjunctive therapy (gluten‑free diet for dermatitis herpetiformis, multidrug regimen for leprosy). Do not discontinue the drug abruptly without medical advice. This information is not a substitute for professional medical advice, diagnosis, or treatment.

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