By Gary M. White, MD
Note: This is a summary only. Please consult the latest information when prescribing.
Dapsone is a drug commonly used in dermatology to treat dermatitis herpetiformis.
25 mg, 100 mg
2-4 days Once daily dosing
One usually starts 50-100 mg/day. Alternatively, one may start low, even only 25 mg/day go up 25 per week.
Metabolized in the liver and excreted in the kidney. It may be prolonged by the enterohepatic circulation.
G6PD, CBC, SGPT, SGOT
Heart condition, e.g. CHF, angina, G6PD deficient
Onset is usually 3-12 weeks after initiation of therapy with a typical dose being 100 mg/day. Patients usually presented with signs of acute infection. Fatalities have occurred.
The constellation of findings in the dapsone syndrome often begin 5-6 weeks after initiation of the drug and include fever, lymphadenopathy, hepatosplenomegaly, hepatitis, and a rash. The rash may take the form of urticaria, erythroderma, maculopapular rash, EM or TEN. If this occurs, dapsone should be stopped and systemic steroids are indicated.
Always occurs to some degree in every patient. Severe anemia may occur in patients with G6PD deficiency. It has been shown that vitamin E 800 Units/day can partially reduce the hemolysis associated with dapsone [AD 1992;128;210].
One usually tries to keep the H/H above 10/30.
Rare above 12-15%. It may be decreased by the addition of cimetidine 400 mg TID (BJD 1993;129;507). Symptoms of methemoglobinemia may occur at or above 3% and can include cyanosis, a grayish color, weakness, headache, tachycardia, nausea and abdominal pain.
Cyanosis of tongue: Dapsone-induced methemoglobinemia in a patient of leprosy. Indian J Dermatol 2015;60:108: At presentation and 2 weeks later after treatment.
Neuropathy may occur distally and is both sensory and motor. It usually occurs within 5 years and at a dose of 300 mg/day. Sulfapyridine does not cause neuropathy and can be used in patients affected with this side effect.
Apprehension, insomnia, irrational speech and a general sense of ill being are signs. The patient may have similar symptoms to sulfapyridine.
Rare, but can be fatal.
Elevated LFTs may occur with dapsone therapy either in conjunction or separate [BJD 1999;141;172] from the dapsone syndrome. Sulphapyridine is an alternative in this situation.
Dapsone has been used in pregnancy for e.g malaria, dermatitis herpetiformis, linear IgA bullous dermatosis and leprosy and appears relatively safe but caution must be taken and dapsone used only if clearly needed.