Intramuscular injection of dapsone in therapy for leprosy: a new approach.

Dapsone is the drug of first choice in the treatment of leprosy. Although the oral route of administration has been mostly used, recent studies of patient compliance revealed that only about 50% of the tables received by the patients are actually taken. It is generally assumed that irregular self-medication favors the development of dapsone resistance. The need for a more reliable route of administration led us to investigate the possibility of an i.m. dapsone depot injection. To achieve effective blood levels for 3-4 weeks, suspensions of large dapsone particles in an aqueous vehicle were made. In a trial with 20 leprosy patients in Nigeria, injection of 900 mg dapsone i.m. as a mixture of particle sizes less than 90 micrometer (20%) and 90-125 micrometer (80%) resulted in a serum level above 0.5 microgram/ml for 18 +/- 5 days with a mean peak concentration of 3.1 +/- 0.9 microgram/ml (n = 10). Injection of 1200 mg of the same particle-size mixture led to peak concentrations of 2.7 +/- 1.0 microgram/ml and maintenance of the level above 0.5 microgram/ml for 25 +/- 3 days (n = 5). After injection of 1200 mg (particle size less than 90 micrometer), serum levels were kept above 0.5 microgram/ml for 21 +/- 5 days with a maximum concentration of 3.9 +/- 1.2 microgram/ml (n = 5). Serum levels were measured using a rapid non-extractive HPLC method. The injections were very well tolerated. Due to these encouraging results, the dosage and formulation will be further optimized.