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Trade Names:
Dapsone
- Tablets 25 mg
- Tablets 100 mg

Mechanism of Action

Pharmacology

Mechanism of action is unknown; however, dapsone is bactericidal and bacteriostatic against Mycobacterium leprae .

Pharmacokinetics

Absorption

Rapidly and nearly completely absorbed from the GI tract, reaching peak plasma concentrations in 4 to 8 h. Administration of 200 mg/day for 8 days achieves plateau levels of 0.1 to 7 mcg/mL.

Distribution

Approximately 70% to 90% bound to plasma protein. The main metabolite, monoacetyl dapsone, is nearly 100% protein bound.

Metabolism

Dapsone is acetylated in the liver, the degree of which is genetically determined.

Elimination

The plasma t _½ ranges from 10 to 50 h. Approximately 70% to 85% is excreted in the urine as conjugates and unidentified metabolites. Enterohepatic circulation accounts for appreciable tissue levels 3 wk after discontinuation of therapy.

Indications and Usage

Treatment of dermatitis herpetiformis; leprosy.

Contraindications

Standard considerations.

Dosage and Administration

PO Start with 50 mg/day in adults and correspondingly smaller doses in children. If full control is not achieved with 50 to 300 mg/day, higher doses may be tried. Reduce dose to minimum maintenance level as soon as possible. The time for dosage reduction is 8 mo (range, 4 mo to 2½ yr of age) and for dosage elimination 29 mo (range, 6 mo to 9 yr of age).

PO 100 mg/day in adults and correspondingly smaller doses in children without interruption in therapy with at least 1 antileprosy drug.

Storage/Stability

Store tablets at controlled room temperature (59° to 86°F).

Drug Interactions

Absorption of dapsone may be decreased, resulting in a loss of efficacy.

Plasma concentrations of both dapsone and trimethoprim may be elevated, increasing the pharmacologic and toxic effects.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Tachycardia.

CNS

Peripheral neuropathy; motor loss; muscle weakness; insomnia; headache; psychosis.

EENT

Blurred vision; tinnitus.

GI

Nausea; vomiting; abdominal pains; pancreatitis; vertigo.

Genitourinary

Albuminuria; nephrotic syndrome; renal papillary necrosis; male infertility.

Hematologic

Hemolysis; increased reticulocyte count; shortened red cell life span; rise in methemoglobin.

Respiratory

Pulmonary eosinophilia.

Miscellaneous

Fever; phototoxicity; hypoalbuminemia; lupus erythematosus; infectious mononucleosis-like syndrome.

Precautions

Pregnancy

Category C .

Lactation

Excreted in breast milk.

Children

Children are treated on the same schedule as adults but with correspondingly smaller doses. Dapsone is generally not considered to have an effect on the later growth and functional development of the child.

Hypersensitivity

Serious cutaneous reactions (eg, erythema multiforme, toxic epidermal necrolysis) resulting from hypersensitivity may occur. In addition, sulfone syndrome, a potentially fatal hypersensitivity with symptoms of fever, malaise, jaundice with hepatic necrosis, exfoliative dermatitis, lymphadenopathy, methemoglobinemia, and hemolytic anemia may occur.

Hepatic Function

Toxic hepatitis or cholestatic jaundice reported and hyperbilirubinemia may occur more frequently in patients with G-6-PD deficiency.

Hematologic

Deaths caused by agranulocytosis, aplastic anemia, and other blood dyscrasias occurred. Treat severe anemia prior to initiation of dapsone therapy.

Hemolysis

Because hemolysis and Heinz body formation may be exaggerated in individuals with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, methemoglobin reductase deficiency or hemoglobin M, give dapsone with caution to patients with these conditions or patients exposed to other agents or conditions (eg, diabetic ketosis) capable of producing hemolysis.

Overdosage

Symptoms

Nausea, vomiting, hyperexcitability, methemoglobin-induced depression, convulsions or severe cyanosis, severe anoxia (with retinal and optic nerve damage).

Patient Information

• Review dosing schedule and prescribed length of therapy with patient.
• Advise patient that medication may be started at a low dose and then gradually increased to provide maximum benefit.
• Instruct patient to continue to take other prescribed medications while taking dapsone.
• Emphasize to patient that treatment will be lengthy and that the entire course of treatment must be completed to avoid relapse or development of resistance.
• Advise patient to take each dose with food if GI upset occurs.
• Instruct patient to stop using and notify health care provider immediately if any of the following symptoms occur: skin rash, sore throat, fever, paleness, purple discoloration of skin, yellowing of skin or eyes, muscle weakness.
• Advise patient that drug may cause blurred vision or dizziness and to use caution while driving or performing other tasks requiring mental alertness until tolerance is determined.