|Systematic (IUPAC) name|
|Bioavailability||70 to 80%|
|Protein binding||70 to 90%|
|Metabolism||Hepatic (mostly CYP2E1-mediated)|
|Half-life||20 to 30 hours|
|(what is this?)|
Dapsone, also known as diaminodiphenyl sulfone (DDS), is an antibiotic commonly used in combination with rifampicin and clofazimine for the treatment of leprosy. It is a second-line medication for the treatment and prevention of Pneumocystis pneumonia and for the prevention of toxoplasmosis in those who have poor immune function. Additionally it has been used for acne as well as other skin conditions. Dapsone is available both topically and by mouth.
Severe side effects may include: a decrease in blood cells, red blood cell breakdown especially in those with glucose-6-phosphate dehydrogenase deficiency (G-6-PD), or hypersensitivity. Common side effects include nausea and loss of appetite. Other side effects include liver inflammation and a number of types of skin rashes. While it is not entirely clear the safety of use during pregnancy some physicians recommend that it be continued in those with leprosy. It is of the sulfone class.
Dapsone was first studied as an antibiotic in 1937. Its use for leprosy began in 1945. It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system. The oral form is available as a generic drug and not very expensive.
Oral dapsone was one of the first medications used to treat moderate to severe acne vulgaris, and is still occasionally prescribed for the treatment of severe cases. A topical form of dapsone is also effective with potentially less side effects.
The dapsone hypersensitivity syndrome develops in 0.5–3.6% of persons treated with the drug, and is associated with a mortality of 9.9%.
The most prominent side-effects of this drug are dose-related hemolysis (which may lead to hemolytic anemia) and methemoglobinemia. About 20% of patients treated with dapsone suffer hemolysis  and the side-effect is more common and severe in those with glucose-6-phosphate dehydrogenase deficiency, leading to the dapsone-containing antimalarial combination Lapdap being withdrawn from clinical use. A case of hemolysis in a neonate from dapsone in breast milk has been reported. Agranulocytosis occurs rarely when dapsone is used alone but more frequently in combination regimens for malaria prophylaxis. Abnormalities in white blood cell formation, including aplastic anemia, are rare, yet are the cause of the majority of deaths attributable to dapsone therapy.
Toxic hepatitis and cholestatic jaundice have been reported by the manufacturer. Jaundice may also occur as part of the dapsone reaction or dapsone syndrome (see below). Dapsone is metabolized by the Cytochrome P450 system, specifically isozymes CYP2D6, CYP2B6, CYP3A4, and CYP2C19. Dapsone metabolites produced by the cytochrome P450 2C19 isozyme are associated with the methemoglobinemia side effect of the drug.
When used topically, dapsone can cause mild skin irritation, redness, dry skin, burning and itching. When used together with benzoyl peroxide products, temporary yellow or orange skin discolorations can occur.
Other adverse effects
Other adverse effects include nausea, headache, and rash (which are common), and insomnia, psychosis, and peripheral neuropathy. Effects on the lung occur rarely and may be serious, though are generally reversible.
The reaction always involves a rash and may also include fever, jaundice, and eosinophilia. In general, these symptoms will occur within the first six weeks of therapy or not at all, and may be ameliorated by corticosteroid therapy.
Mechanism of action
As an antibacterial, dapsone inhibits bacterial synthesis of dihydrofolic acid, via competition with para-aminobenzoate for the active site of dihydropteroate synthetase. Though structurally distinct from dapsone, the sulfonamide group of antibacterial drugs also work in this way.
When used for the treatment of skin conditions in which bacteria do not have a role, the mechanism or action of dapsone is not well understood. Dapsone has anti-inflammatory and immunomodulatory effects, which are thought to come from the drug's blockade of myeloperoxidase. This is thought to be its mechanism of action in treating dermatitis herpetiformis.
As part of the respiratory burst that neutrophils use to kill bacteria, myeloperoxidase converts hydrogen peroxide (H
2) into hypochlorous acid (HOCl). HOCl is the most potent oxidant generated by neutrophils, and can cause significant tissue damage during inflammation. Dapsone arrests myeloperoxidase in an inactive intermediate form, reversibly inhibiting the enzyme. This prevents accumulation of hypochlorous acid, and reduces tissue damage during inflammation.
Though dapsone is an anti-inflammatory agent and not a steroid, it does not fit the usual definition of an NSAID. By definition, NSAIDs block cyclo-oxygenase as their primary mechanism of action, which dapsone does not do.
Dapsone is an odorless white to creamy-white crystalline powder with a slightly bitter taste.
Certain patients are at higher risks of adverse effects when using dapsone. Some specific issues that should be considered are:
- Related to the blood (a full blood count should be obtained prior to initiating therapy):
- Related to the liver (obtain liver function tests before starting therapy):
- Liver impairment
- Related to allergy:
- Sulfonamide allergy is associated with dapsone allergy
People with diabetes mellitus have been seen to exhibit unexpectedly low HbA1c results when taking Dapsone, and HbA1c i an unreliable test in states of increased red cell turnover, e.g. a drug induced haemolytic anaemia.
In the early 20th century, the German chemist Paul Ehrlich was developing theories of selective toxicity based largely on the ability of certain dyes to kill microbes. Gerhard Domagk, who would later win a Nobel Prize for his efforts, made a major breakthrough in 1932 with the discovery of the antibacterial prontosil red (sulfonamidochrysoidine). Further investigation into the involved chemicals opened the way to sulfa drug and sulfone therapy, first with the discovery of sulfanilamide, the active agent of prontosil, by Daniel Bovet and his team at Pasteur Institute (1935), then with of dapsone independently by Ernest Fourneau in France and Gladwin Buttle in United-Kingdom.
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