Dapsone

What is dapsone?

Dapsone is a sulphone antibiotic available for many years to treat leprosy. In New Zealand, 100 mg and 25 mg tablets are available.

What is dapsone used for in dermatology?

Dapsone is used to treat various skin conditions including:

• Dermatitis herpetiformis
• Linear IgA bullous dermatosis
• Vasculitis
• Pyoderma gangrenosum
• Sweet disease
• Aphthous ulceration
• Granuloma annulare.

Contraindications to dapsone

Dapsone should not be taken by anyone that is allergic to dapsone. Some patients with sensitivity to other sulphone antibiotics can tolerate dapsone. 

The dose of dapsone may need to be lower than normal in people with significant heart or lung disease. This is due to the drug's effect on the oxygen-carrying capacity of blood cells.

Dapsone should be avoided during pregnancy and breast feeding.

Laboratory monitoring while on dapsone

Dapsone treatment requires careful laboratory monitoring.

Pretreatment

• Glucose-6-phosphate dehydrogenase status
• Full blood count  
• Liver function tests

After one week, then monthly for the first 3 months:

• Full blood count (a small drop in haemoglobin is usual)
• Liver function tests.

Note that the use of glycosylated haemoglobin (HbA1c) to monitor diabetes mellitus is unreliable on dapsone.

Side effects of dapsone

Minor, relatively frequent side effects

• Gastrointestinal upset including nausea or vomiting
• A headache
• Blue discolouration of lips and fingertips

Side effects of greater importance

• Anaemia (low haemoglobin or blood count) is common in patients receiving dapsone; it is usually mild. Possible symptoms of anaemia include tiredness and shortness of breath. More severe anaemia is likely in patients with glucose-6-phosphate dehydrogenase deficiency.
• Allergy may cause a widespread skin rash. It is rarely associated with potentially fatal severe drug hypersensitivity syndrome, in which there is prolonged rash, fever, swollen lymph glands and internal organ failure (liver, lungs, heart, kidneys).
• Uncommonly, weakness of the foot and hand muscles can occur, particularly with long term dapsone therapy with doses greater than 100 mg per day. Once per week it is advisable to test your ability to walk on your tip-toes and to test your hand grip strength.
• It has been reported to cause renal papillary necrosis (kidney disease).
• Psychosis (hallucinations or delusions) has been reported.

Rare, but potentially serious side effects

• A significant decrease in the white blood count typically presents with fever, sore throat, skin infections, or other local signs of infection. Commonly a widespread red skin rash is also present.
• Rarely, an illness resembling glandular fever develops, causing severe fatigue, fever, sore throat, rash and prominent lymph glands.

Dapsone gel

Dapsone gel 7.5% once daily (trade name Aczone®) is available in the US and Australia for the topical treatment of acne. It is usually well tolerated but rarely causes the skin at the site of application to become dry and red. There is a low risk of haemolysis and the other side effects of oral treatment described above.