Dapsone monitoring

Trimethoprim has been reported to decrease the therapeutic effect of cyclosporine with a concomitant increased risk of nephrotoxicity. Increased levels of dapsone, warfarin, methotrexate, zidovudine, and sul-fonylureas may occur when given together with trimethoprim dosages of these drugs should be modified and the patient monitored accordingly. 

PROBENECID DAPSONE t dapsone levels, with risk of bone marrow suppression Uncertain Monitor FBC closely... 

DAPSONE ANTIVIRALS-ZIDOVUDINE Possible t adverse effects when co administered with zidovudine Uncertain possible T bioavailability of zidovudine Use with caution monitor for peripheral neuropathy... 

Dapsone/warfarin/quinidine Decreased metabolism of the other agent Monitor warfarin/avoid others... 

The documentation is very limited. It is likely that the probenecid will raise the serum levels of dapsone given long-term. The importance of this is uncertain, but the extent of the rise and the evidence that the haematological toxicity of dapsone may be related to dapsone levels suggests that it may well have some clinical importance. It would therefore seem prudent to monitor for dapsone adverse effects if probenecid is also given. 

The interaction between dapsone and rifampicin is established but of uncertain clinical importance. Concurrent use should be well monitored to confirm that treatment is effective. It may be necessary to raise the dosage of dapsone. It has been pointed out that there is the risk of treatment failures for Pneumocystis pneumonia as well as for leprosy. Also be alert for any evidence of methaemoglobinaemia. 

A pharmacokinetic study in 12 TUV-positive patients who were given zalcitabine 1.5 mg three times daily and dapsone 100 mg daily, alone or together, found that dapsone did not significantly affect the kinetics of the zalcitabine. However, zaleitabine deeieased the clearance of dapsone by 21%, increased its maximum serum levels by 19% and increased its half-life by 34%. These changes are relatively small and seem unlikely to have much clinical relevance, but until this is confirmed it would seem prudent to monitor the concurrent use of these two drugs. The UK manufacturer recommended caution with the combination because of the possibility of an increased risk of peripheral neuropathy the US manufacturer advised avoiding the combination where possible. ... 

Dapsone 100 mg daily had no effect on the pharmacokinetics of a single 200-mg dose of zidovudine in 8 TUV-positive subjects. In a further study, which considered the safety of dapsone in combination with zidovudine, dapsone was shown to increase the risk of zidovudine-related blood dys-crasias. Therefore it would seem that dapsone and zidovudine can be given concurrently, but monitoring for an increase in adverse events would seem advisable. 

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