Indications
- Leprosy (FDA-approved).
- Dermatitis herpetiformis (FDA-approved ).
- Bullous eruption of SLE : 50 mg daily.
- Linear IgA bullous dermatosis.
- Erythema elevatum diutinum.
- Behçet disease.
- Cutaneous small vessel vasculitis.
- Mucous membrane (cicatricial) pemphigoid.
- IgA pemphigus.
- Sweet syndrome.
- Pyoderma gangrenosum.
- Subacute cutaneous lupus erythematosus.
- Relapsing polychondritis.
- Granuloma annulare.
- Granuloma faciale.
- Rosacea (granulomatous).
- Pustular psoriasis.
- Panniculitis.
- Nodulocystic acne.
Dosage
- Most conditions require 50–200 mg/day.
Mechanism of action
- Dapsone is most useful in the treatment of dermatologic diseases involving neutrophilic infltrates.
- It inhibits neutrophil myeloperoxidase, thus reducing damage from the neutrophil respiratory burst mediated by this enzyme.
- Dapsone inhibits neutrophil chemotaxis to N-formyl-methionyl-leucyl-phenylalanine (fMLP) and to interfere with the CD11b/CD18-mediated neutrophil binding that induces chemoattractant signal transduction.
- It also inhibits eosinophil myeloperoxidase activity.
Baseline Monitoring
- Any cardiopulmonary or neurologic symptoms should be assessed prior to therapy.
- Complete blood count.
- Liver function tests.
- G6PD level.
- Renal function tests
Follow Up Monitoring
- CBC with differential every week for four weeks, then every two weeks until week 12, then every 3 to 4 months.
- Reticulocyte count if anemia develops.
- Liver function tests every 3–4 months.
- Renal function tests every 3–4 months.
Each visit :
- Assessment of peripheral motor function.
- Evaluation for the signs and symptoms of methemoglobinemia.
- Assessment for peripheral neuropathy (e.g. motor strength,reflexes).
- Methemoglobin level if clinically indicated.
- Increase monitoring frequency when dose is increased.
Side effects
- Blood (common)
- Hemolysis, methemoglobinemia (symptoms include headache, lethargy).
- GIT(uncommon)
- dyspepsia, anorexia.
- Rare
- Agranulocytosis (idiosyncratic reaction).
- Peripheral neuropathy, Dapsone hypersensitivity syndrome.
Contraindications
- Absolute
- Prior hypersensitivity to dapsone.
- Relative
- Low (G6PD) level.
- Significant cardiopulmonary disease.
- Allergy to sulfonamide antibiotics.
- Signifcant liver or renal function impairment.
- Pre-existing peripheral neuropathy.
Interactions
- Drugs that may increase dapsone levels (and side effects) are probenecid (via decreased renal clearance), trimethoprim, and other folate antagonists such as methotrexate.
- Sulfonamides and hydroxychloroquine increase the oxidative stress on RBCs and may worsen hemolysis.
- Dapsone levels may be reduced by activated charcoal, paraaminobenzoic acid (PABA), and rifampin.
Pregnancy &Lactation
- Pregnancy category C.
- Dapsone is able to cross the placenta and is excreted into breast milk.
- However, it is approved by the American Academy of Pediatrics for use during lactation when required.
- Hemolysis has been demonstrated to occur in nursing infants of mothers taking dapsone.
Precautions
- Patients must be warned against self-medication and self adjustment of the dosage of dapsone in response to small changes in disease activity.
- They should be instructed to discontinue the medication if they develop persistent fevers or flu-like symptoms.
- Patients should be educated about DHS and instructed to discontinue therapy and notify their medical provider if any signs or symptoms of the dapsone hypersensitivity syndrome develop.
Drug Info
- Dapsone has along elimination half-life >> remaining in the circulation for as long as 30 days after a single oral dose.
- The major hemotoxicity of dapsone is related to the N-hydroxy metabolites of dapsone.
- Dapsone-induced hemolysis is that it may result in falsely low levels of HgbA1c in patients with poorly controlled diabetes mellitus.
- There is not a clear relationship between the hemolytic anemia associated with dapsone and the formation of methemoglobin
- Vitamin E (800 IU daily) may provide a small amount of protection against the formation of methemoglobin and hemolysis.
- Cimetidine (400 mg 3 times daily) has been demonstrated to reduce methemoglobin formation in humans.
- In an emergency, oral methylene blue (100–300 mg daily) can also be used acutely to reduce methemoglobin levels, although this drug is contraindicated and ineffective if the patient is G6PD defcient.
- Granulocyte colony-stimulating factor (G-CSF) has been used successfully to speed granulocyte recovery in case of agranulocytosis.
- Most patients recover completely from peripheral neuropathy with discontinuation of the dapsone, which can take from several weeks to up to 2 years.