Dapsone is a sulphone antibiotic medication available for many years to treat leprosy. In New Zealand, 100mg and 25mg tablets are available.
Dapsone is also used for treating various skin conditions including:
- Dermatitis herpetiformis
- Linear IgA bullous dermatosis
- Pyoderma gangrenosum
- Sweet disease
- Aphthous ulceration
- Granuloma annulare
Dapsone treatment requires careful laboratory monitoring.
It has some important side effects, which are more likely with higher doses. If you are on dapsone, follow your doctor's instructions carefully, and let him or her know if you start any new medications.
You should not take dapsone if you are allergic to it. Let your doctor know if you are allergic to sulphur antibiotics - dapsone is usually well tolerated, but it should be started cautiously.
If you have significant heart or lung disease, the dose of dapsone may have to be lower because of the drug's effect on oxygen carrying capacity of your blood cells.
Dapsone should be avoided during pregnancy and breast feeding.
Side effects: minor, relatively infrequent
- Gastrointestinal upset including nausea or vomiting.
- 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. It is possibly less likely if you are taking antioxidants such as ascorbic acid (vitamin C) or cimetidine tablets. Possible symptoms of anaemia include tiredness and shortness of breath. More severe anaemia is likely if you have a rare condition known as glucose-6-phosphate dehydrogenase (G6PD) 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.
- Rarely, 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.
- Tell your doctor promptly if these symptoms occur.
Usually, a blood test is performed as a base-line before starting dapsone. It is then checked after about a week on therapy, and then about once a month, depending on the dose and state of the blood count.
Follow instructions precisely regarding the timing of these tests.
Dapsone gel 5% (trade name Aczone®) is available in the US for topical treatment of acne. It is usually well tolerated, but sometimes 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.