Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2019 Publisher: Accord-UK Ltd (Trading style: Accord), Whiddon Valley, Barnstaple, Devon, EX32 8NS
Dapsone is a sulfone active against a wide range of bacteria.
Dapsones mechanism of action is probably similar to that of the sulfonamides which involves inhibition of folic acid synthesis in susceptible organisms. It is usually considered to be bacteriostatic against M leprae although it may also possess weak bactericidal activity. It is also active against Plasmodium and Pneumocystis carinii. As with sulfonamides, antibacterial activity is inhibited by p-aminobenzoic acid.
Dapsone is almost completely absorbed from the GI tract with peak plasma concentrations occurring about 2-8 hours after a dose. Steady-state concentrations are not obtained until after at least 8 days of daily administration; doses of 100mg daily provide trough concentrations of 0.5 micrograms/ml. About 50-80% of dapsone in the circulation is bound to plasma proteins and nearly 100% of its monoacetylated metabolite is bound. Dapsone undergoes enterohepatic recycling. It is widely distributed; is present in saliva, breast milk and crosses the placenta. The half-life ranges from 10-80 hours. Dapsone is acetylated to monoacetyldapsone, the major metabolite, and other mono and diacetyl derivatives. Acetylation exhibits genetic polymorphism. Hydroxylation is the other major metabolite pathway resulting in hydroxylamine dapsone which may be responsible for dapsone-associated methaemoglobinaemia and haemolysis. Dapsone is mainly excreted in the urine, only 20% of a dose as unchanged drug.
There are no pre-clinical data of relevance to the prescriber which are additional to that already included in other sections of the SPC.
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