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Dapsone (Aczone)

Dapsone, a synthetic sulfone, is an antimycobacterial and antiprotozoal agent.



Hematologic Effects

The most frequent adverse effects of dapsone are dose-related hemolytic anemia and methemoglobinemia. Hemolysis occurs in most patients receiving 200 mg or more of dapsone daily; however, symptomatic anemia occurs only occasionally. The manufacturer states that the hemoglobin level is generally decreased by 1-2 g/dL, the reticulocyte count is increased 2-12%, erythrocyte life span is shortened, and methemoglobinemia occurs in most patients receiving dapsone. Heinz body formation also occurs frequently. Unless severe, hemolysis or methemoglobinemia does not generally require discontinuance of dapsone therapy.

These adverse hematologic effects occur in patients with or without glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, but are most severe in patients with G-6-PD deficiency. Hemolysis and Heinz body formation may be exaggerated in patients with G-6-PD deficiency, methemoglobin reductase deficiency, or hemoglobin M. Hemolysis and methemoglobinemia may be poorly tolerated by patients with severe cardiopulmonary disease. In addition, dapsone-induced adverse hematologic effects may be poorly tolerated by some patients with acquired immunodeficiency syndrome (AIDS) receiving the drug for the treatment of Pneumocystis jiroveci (formerly Pneumocystis carinii) pneumonia, since such patients may have preexisting anemia and/or hypoxemia.

Generally, however, dapsone is well tolerated in AIDS patients, although asymptomatic methemoglobinemia has been reported in two-thirds of such patients receiving 100 mg of dapsone daily concomitantly with trimethoprim 20 mg/kg daily.

Methemoglobinemia has been reported substantially less frequently in AIDS patients receiving dapsone alone. A substantial proportion of AIDS patients who do not tolerate co-trimoxazole are able to tolerate dapsone. Cyanosis, which is usually associated with mild methemoglobinemia, may occur during dapsone therapy. Acute methemoglobinemia occurs rarely, but may result in anemia, vascular collapse, and death. Unless the patient has G-6-PD deficiency, acute methemoglobinemia should be treated with IV methylene blue. (See Acute Toxicity: Treatment.)

Prophylactic administration of ascorbic acid, folate, and iron reportedly may prevent some of the adverse hematologic effects of dapsone. Leukopenia has been reported occasionally during therapy with dapsone, and potentially fatal agranulocytosis and aplastic anemia have been reported rarely.

Leprosy Reactional States

Effective therapy of leprosy with dapsone or other antileprosy agents generally results in abrupt changes in the clinical state of the patient. These changes have been termed leprosy reactional states and can be classified into 2 types: reversal reactions (type 1) and erythema nodosum leprosum (ENL) reactions (type 2). Reversal reactions (type 1) occur mainly in borderline or tuberculoid leprosy patients.

Reversal reactions presumably occur because the patient is able to mount an enhanced delayed hypersensitivity response to the residual infection and this leads to swelling of existing skin and nerve lesions. Existing lesions become erythematous and edematous and may ulcerate; fever and an increased leukocyte count frequently occur, and acute neuritis and loss of nerve function may develop. ENL is a recurrent immunologically mediated syndrome that occurs principally in patients with multibacillary leprosy.

While ENL reactions have been reported to occur in 10-50% of lepromatous leprosy patients and 25-30% of borderline lepromatous patients, these reactions are being reported less frequently in patients receiving the currently recommended multidrug antileprosy regimens that include clofazimine than in patients who received dapsone monotherapy. These reactions are considered to be a manifestation of the disease rather than an adverse reaction to antileprosy regimens. T

reatment of leprosy reactional states depends on the severity of manifestations; severe reactions generally require hospitalization. In general, the usual antileprosy regimen is continued despite the occurrence of a leprosy reactional state and, if nerve injury or skin ulceration is threatened, corticosteroids are administered. Analgesics, corticosteroids, or surgical decompression of swollen nerve trunks are generally used to suppress reversal reactions.

ENL reactions generally are treated using analgesics, corticosteroids, and/or thalidomide; clofazimine also has anti-inflammatory effects and is beneficial in the treatment of ENL reactions. Early diagnosis and treatment of leprosy reactional states are important since these reactions are associated with considerable morbidity, especially if chronic, recurrent ENL occurs. Therapy for leprosy and leprosy reactional states should be undertaken in consultation with an expert in the treatment of leprosy.

Dermatologic Reactions

Adverse cutaneous effects, which usually result from sensitization to dapsone, occur rarely during therapy with the drug. Cutaneous reactions include exfoliative dermatitis, toxic erythema, erythema multiforme, toxic epidermal necrolysis, morbilliform and scarlatiniform eruptions, urticaria, and erythema nodosum. If a new or toxic dermatologic reaction occurs during therapy with dapsone, the drug should be discontinued and appropriate therapy initiated. Rash reportedly occurs in about 30-40% of AIDS patients receiving dapsone concomitantly with trimethoprim, but less frequently in those receiving dapsone alone; despite such rash, a substantial proportion of patients who do not tolerate co-trimoxazole are able to tolerate dapsone.

Nervous System Effects

Peripheral neuropathy with motor loss has been reported rarely in patients receiving high dosage of dapsone (200-500 mg daily). If muscle weakness occurs during therapy with dapsone, the drug should be discontinued; complete recovery may occur if the drug is withdrawn, but may take many months to several years. The mechanism of recovery is reportedly by axonal regeneration, and some recovered patients have tolerated retreatment with dapsone using a lower dosage of the drug.

Although peripheral neuropathy has not been reported to date in patients with leprosy receiving dapsone, presumably because lower dosage is used, this adverse effect may be difficult to distinguish from a leprosy reactional state. Insomnia, headache, nervousness, vertigo, and psychosis have also been reported with dapsone.

GI Effects

Adverse GI effects including anorexia, abdominal pain, nausea, and vomiting have occurred in patients receiving dapsone.

Hepatic Effects

Toxic hepatitis and cholestatic jaundice have been reported with dapsone. Cholestatic jaundice may be a hypersensitivity reaction, and generally appears to be reversible following discontinuance of the drug. Adverse hepatic effects have occurred shortly after initiation of dapsone therapy and may be manifested by increased serum concentrations of alkaline phosphatase, AST (SGOT), bilirubin, and LDH. Liver function test abnormalities reportedly occur more frequently during combined dapsone and trimethoprim therapy than during dapsone alone. Hyperbilirubinemia has also occurred during dapsone therapy and may occur more often in patients with G-6-PD deficiency.

Renal and Electrolyte Effects

Albuminuria, nephrotic syndrome, and renal papillary necrosis have occurred rarely during dapsone therapy. Mild, generally asymptomatic hyperkalemia has been reported frequently in patients receiving combined dapsone and trimethoprim therapy, but serum potassium concentrations generally returned to normal during continued therapy.

Other Adverse Effects

Blurred vision, tinnitus, fever, phototoxicity, hyperpigmented macules, hypoalbuminemia without proteinuria, drug-induced lupus erythematosus, and an infectious mononucleosis-like syndrome have been reported with dapsone. Tachycardia has also occurred with dapsone, particularly with excessive dosage of the drug.

Precautions and Contraindications

Dapsone is contraindicated in patients who are hypersensitive to the drug or dapsone derivatives such as sulfoxone sodium. Dapsone should not be administered to patients with severe anemia; the anemia should be treated prior to initiation of dapsone therapy.

Dapsone should be used with caution in patients with G-6-PD deficiency, methemoglobin reductase deficiency, or hemoglobin M.

Dapsone should also be used with caution in patients who are exposed to other drugs or agents that are capable of inducing hemolysis and in patients with conditions associated with hemolysis (e.g., certain infections, diabetic ketosis).

Some clinicians recommend that screening for G-6-PD deficiency be performed prior to initiating dapsone therapy in human immunodeficiency virus (HIV)-infected patients, and that hemoglobin and methemoglobin concentrations and hematocrit be monitored periodically in such patients, particularly those receiving the drug concomitantly with trimethoprim. Complete blood cell counts (CBCs) should be performed frequently during dapsone therapy.

Some clinicians recommend that CBCs be performed weekly during the first month of therapy, monthly for the next 6 months, and every 6 months thereafter. If a substantial reduction in leukocytes, platelets, or hematopoiesis is evident, dapsone should be discontinued and the patient closely monitored. Because toxic hepatitis and cholestatic jaundice have been reported with dapsone, liver function should be monitored, when feasible, before and during therapy with the drug. If any abnormality in liver function is evident, the drug should be discontinued until the source of the abnormality is established.

Patients should be instructed to report to their clinician the presence of sore throat, fever, pallor, purpura, or jaundice during dapsone therapy.

Mutagenicity and Carcinogenicity

Dapsone was not mutagenic in microbial tests using Salmonella typhimurium, with or without microsomal activation. Dapsone has been found to be carcinogenic in animal studies. The drug has caused mesenchymal tumors in the spleen and peritoneum of male rats and female mice and thyroid carcinoma in female rats.

Pregnancy, Fertitlity and Lactation

Animal reproduction studies have not been performed with dapsone. Although dapsone has been used in pregnant women without evidence of fetal abnormalities, the drug should be used during pregnancy only when clearly needed. In patients with leprosy, some clinicians consider that the benefits of maintaining dapsone therapy during pregnancy outweigh the potential risks to the fetus. Infertility has been reported in males receiving dapsone; in 2 patients, fertility was restored following discontinuance of the drug.

Because dapsone is distributed into milk and because of the tumorigenic potential demonstrated in animal studies, dapsone should not be used in nursing women. A decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.

Drug Interactions


Failure of dapsone to prevent Pneumocystis jiroveci (formerly Pneumocystis carinii) pneumonia was reported in about 40% of human immunodeficiency virus (HIV)-infected patients who were enrolled in treatment IND or open-label studies with didanosine (ddI, dideoxyinosine) and received the drugs concomitantly.

This failure rate was substantially higher than that reported in other studies in which dapsone was not administered with didanosine and than that observed in didanosine-treated patients receiving co-trimoxazole or aerosolized pentamidine for the prevention of PCP. While the mechanism(s) of this potential interaction requires further elucidation, and dapsone pharmacokinetic determinations were not performed in the treatment IND or open-label studies, it was suggested that the buffer system present in the didanosine preparation, which provides a pH of 7-8 to facilitate GI absorption of the antiviral agent, interferes with GI absorption of dapsone.

Dapsone is insoluble at neutral pH, while solubility is facilitated at acidic pH. Similar interference with ketoconazole GI absorption, which like dapsone’s is facilitated at acidic pH, has been reported during concomitant therapy with the buffered didanosine preparation; administering ketoconazole at least 2 hours before didanosine can minimize this potential interaction.

Therefore, pending further accumulation of information on the potential interaction between dapsone and didanosine, it has been suggested that dapsone administration be separated from that of buffered didanosine by at least 2 hours.

Pharmacokinetic studies currently are under way in an attempt to elucidate the underlying mechanism(s) of this interaction.


Results of several studies indicate that concomitant clofazimine does not affect the pharmacokinetics of dapsone, although a transient increase in urinary excretion of dapsone reportedly occurred in a few patients receiving concomitant therapy with the drugs. In a study in lepromatous leprosy patients receiving dapsone (100 mg daily) and rifampin (600 mg daily), concomitant administration of clofazimine (100 mg daily) did not affect plasma dapsone concentrations or the plasma half-life or urinary elimination of dapsone.

There is some evidence that dapsone may decrease or nullify some of the anti-inflammatory effects of clofazimine. In vitro, clofazimine and dapsone have opposing effects on neutrophil motility and lymphocyte transformation. Some clinicians suggest that this theoretically could adversely affect the efficacy of clofazimine in patients with erythema nodosum leprosum (ENL) reactions. Several borderline leprosy and lepromatous leprosy patients with severe, recurrent ENL reactions reportedly required higher clofazimine dosage to control these reactions when dapsone therapy was given concomitantly than when clofazimine was given alone.

The manufacturer of clofazimine, however, suggests that further study is needed to confirm this interaction and states that it is advisable to continue treatment with both clofazimine and dapsone in patients who develop leprosy-associated inflammatory reactions, including ENL, during concomitant therapy with the drugs. There is no evidence to date that dapsone and clofazimine interfere with the antimycobacterial activity of each other.

Drugs Associated with Adverse Hematologic Effects

Because the drugs have similar adverse hematologic effects, concurrent use of a folic acid antagonist (e.g., pyrimethamine) and dapsone may result in an increased risk of these adverse effects. Agranulocytosis has developed during the second and third months of therapy in patients receiving concomitant treatment with weekly pyrimethamine and dapsone. If pyrimethamine is used concomitantly with dapsone, the patient should be monitored more frequently than usual for adverse hematologic effects. Because effects may be additive, dapsone should be used with caution in patients with G-6-PD deficiency receiving or exposed to other drugs or agents which are capable of inducing hemolysis in these individuals (e.g., nitrite, aniline, phenylhydrazine, naphthalene, niridazole, nitrofurantoin, primaquine).


The clinical importance has not been determined to date, but rifampin reportedly decreases serum dapsone concentrations by inducing liver enzymes responsible for inactivation of the sulfone and increases urinary excretion of the sulfone. Although serum dapsone concentrations may be 7-10 times lower when rifampin is administered concurrently, the manufacturer of dapsone and some clinicians state that a change in dapsone dosage generally is not required during concomitant therapy in patients with leprosy.


Trimethoprim may increase plasma dapsone concentrations during concomitant therapy and potentially may increase the risk of adverse effects. However, such combined therapy also appears to be associated with improved efficacy for the treatment of PCP compared with dapsone alone. In a non-crossover study in patients with AIDS receiving oral dapsone alone (100 mg daily) or combined with oral trimethoprim (20 mg/kg daily) for 21 days in the treatment of PCP, plasma dapsone concentrations were 40% higher in those receiving combined therapy than in those receiving dapsone alone.

In addition, methemoglobinemia occurred more frequently (67 versus 11%, respectively) as did discontinuance of therapy secondary to adverse effects (30 versus 0%, respectively) in patients receiving combined therapy versus dapsone alone.

The risk of other dapsone-associated adverse effects also may be increased by combined dapsone and trimethoprim therapy. Generally, however, such therapy is well tolerated, although periodic monitoring for potential toxicity (e.g., methemoglobinemia) is recommended. Dapsone also may increase plasma trimethoprim concentrations, but an increased risk of adverse effects attributable to the latter drug was not identified in this study. Further pharmacokinetic studies are needed to determine dosages of combined therapy that can optimize efficacy while minimizing potential toxicity.

Other Drugs

While there was limited preliminary evidence that probenecid might interfere with urinary excretion of acid-labile metabolites of dapsone, any such potential interaction subsequently has not been adequately documented and therefore is considered unlikely and/or clinically irrelevant.

Acute Toxcicity


Overdosage of dapsone generally results in nausea, vomiting, and hyperexcitability within a few minutes to up to 24 hours later. Methemoglobin-induced depression, seizures, and severe cyanosis may occur and require prompt treatment. Hemolysis may occur 7-14 days after an acute ingestion.


In patients who do not have G-6-PD deficiency, dapsone-induced methemoglobinemia should be treated with methylene blue (1-2 mg/kg given by slow IV injection). The effect is generally complete within 30 minutes, but methylene blue may need to be readministered if methemoglobin reaccumulates.

Alternatively, in nonemergency situations, methylene blue may be given orally in a dosage of 3-5 mg/kg every 4-6 hours. Methylene blue should not be administered to patients with G-6-PD deficiency, since methylene blue reduction depends on G-6-PD. Orally administered activated charcoal (20 g 4 times daily) has been shown to substantially enhance the elimination of dapsone and its monoacetyl derivative in several cases of acute dapsone overdosage, and some clinicians recommend it as a treatment of choice in the management of acute dapsone intoxication. Hemodialysis also enhances the elimination of dapsone and its monoacetyl derivative.

Mechanism of Action

Dapsone is usually bacteriostatic in action. The mechanism of action of dapsone has not been fully elucidated. Because the antibacterial activity of dapsone is inhibited by p-aminobenzoic acid (PABA), the drug probably has a mechanism of action similar to that of sulfonamides which involves inhibition of folic acid synthesis in susceptible organisms. Some studies indicate that dapsone may inhibit the alternate pathway of complement activation and interfere with the myeloperoxidase-H2O2-halide-mediated cytotoxic system within neutrophils. In vitro studies indicate that dapsone stimulates neutrophil motility.

The drug also appears to inhibit spontaneous and induced synthesis of prostaglandin E2 by polymorphonuclear leukocytes obtained from healthy individuals or patients with leprosy. The mechanism of action of dapsone in the treatment of dermatitis herpetiformis is unknown; however, dapsone only suppresses the disease, and cutaneous IgA and complement deposition are not affected by the drug. It has been suggested that dapsone may act as an immunomodulator when used in the treatment of dermatitis herpetiformis and other dermatologic diseases.


Dapsone is active in vivo against Mycobacterium leprae. M. leprae cannot be cultured in vitro, but in vivo mouse footpad studies using M. leprae recovered from untreated patients with leprosy indicate that dapsone concentrations of 1-10 ng/mL generally inhibit susceptible strains of the organism.

Dapsone is also active against M. tuberculosis and several other species of mycobacteria. In vitro, most susceptible strains of M. tuberculosis are inhibited by dapsone concentrations of 10 mcg/mL.

Dapsone also has some activity against Pneumocystis jiroveci (formerly Pneumocystis carinii) and Plasmodium.


Resistant strains of initially susceptible M. leprae may develop during therapy with dapsone; resistance to the drug appears to develop in a slow, stepwise manner. It has been estimated that resistance to dapsone develops in 2-10% of patients with lepromatous leprosy who have received dapsone alone for many years. Resistance has been reported to occur as long as 5-24 years after initiation of dapsone therapy; resistance has been reported most frequently when the drug was given in low dosage or intermittently.

Although primary resistance to dapsone used to be reported only rarely, resistance to the drug has been reported with increasing frequency in M. leprae recovered from newly diagnosed cases of leprosy in patients who have not previously received therapy with a sulfone. Cross-resistance between dapsone and clofazimine has not been reported to date. However, M. leprae resistant to both dapsone and clofazimine, but susceptible to rifampin, has been reported rarely.



Following oral administration, dapsone is almost completely absorbed from the GI tract and peak serum concentrations of the drug are generally attained within 2-8 hours. Steady-state serum concentrations of dapsone range from 0.1-7 mcg/mL and average 2.3 mcg/mL after 8 days of therapy with a dosage of 200 mg daily.

Following oral administration of a single 100-mg oral dose of dapsone, serum concentrations of the drug range from 0.4-1.2 mcg/mL 24 hours after the dose. Trace amounts of dapsone may be found in serum for 8-12 days after oral administration of a single 200-mg dose of the drug or for as long as 35 days after discontinuance of repeated doses of the drug.

Dapsone and its monoacetyl metabolite (MADDS) appear to undergo enterohepatic circulation.


The volume of distribution of dapsone is reportedly 1.5-2.5 L/kg in adults.

Dapsone is distributed into most body tissues.

Dapsone is reportedly retained in skin, muscle, kidneys, and liver; trace concentrations of the drug may be present in these tissues up to 3 weeks after discontinuance of dapsone therapy.

Dapsone is also distributed into sweat, saliva, sputum, and tears.

The drug is also distributed into bile. Although in one study using radiolabeled dapsone in patients with leprosy, higher concentrations of radioactivity were attained in diseased than in presumably healthy skin, other studies indicate little or no difference in sulfone content of healthy and diseased skin in patients with leprosy. Dapsone may not penetrate ocular tissue well, since eye lesions may develop or progress during therapy of leprosy even though the disease may be controlled or eliminated in other tissues. Dapsone crosses the placenta.

Dapsone is distributed into milk, and 1.1 mcg/mL of the drug has been reported in the milk of a woman receiving 50 mg of dapsone daily; concurrent maternal serum concentrations of the drug were 1.6 mcg/mL. Dapsone is 50-90% bound to plasma proteins. The major metabolite of dapsone, monoacetyldapsone, is almost completely bound to plasma proteins.


There are large interindividual variations in the plasma half-life of dapsone. The plasma half-life of dapsone may range from 10-83 hours and averages 20-30 hours. Dapsone is acetylated in the liver to monoacetyl and diacetyl derivatives. The major metabolite of dapsone is monoacetyldapsone (MADDS). The rate of acetylation of dapsone is genetically determined and is subject to interindividual variation, although the rate is usually constant for each individual. The drug also is hydroxylated in the liver to hydroxylamine dapsone (NOH-DDS). NOH-DDS appears to be responsible for methemoglobinemia and hemolysis induced by the drug.

Approximately 20% of each dose of dapsone is excreted in urine as unchanged drug, 70-85% is excreted in urine as water-soluble metabolites, and a small amount is excreted in feces.

Dapsone is excreted in urine as acid-labile mono-N-glucuronide and mono-N-sulfamate derivatives in addition to some unidentified metabolites. Orally administered activated charcoal has been shown to substantially enhance the elimination of dapsone and its monoacetyl derivative in healthy adults and in several cases of acute dapsone overdosage. Hemodialysis also reportedly enhances the elimination of dapsone and its monoacetyl derivative.

Chemistry and Stability


Dapsone is a synthetic sulfone anti-infective. Dapsone occurs as a white or creamy white, crystalline powder that has a slightly bitter taste. The drug is very slightly soluble in water and freely soluble in alcohol.


Dapsone may discolor following exposure to light. Although no chemical change is detectable following discoloration, the drug should be protected from light. Dapsone tablets should be stored in well-closed, light-resistant containers at a temperature less than 40°C, preferably between 15-30°C.


Dapsone Oral Tablets 25 mg Dapsone Tablets, (scored)  Jacobus 100 mg Dapsone Tablets, (scored) Jacobus

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