Dear Dr. Feinberg, How does a physician determine what the first line of pharmacological treatment for PCP (pneumocystis carinii pneumonia) infection is? Is Dapsone usually the first choice, or does it depend on other interpatient variable factors? I'm just curious as to how many physicians actually prescribe Dapsone as the first line of treatment for PCP. Thanks.

I'm not clear whether you are talking about prevention (prophylaxis) or treatment of established PCP. However, in both situations, dapsone is second choice after trimethoprim/sulfamethoxazole (Bactrim, Septra). For prevention, dapsone is used alone, but for treatment of active PCP, dapsone is used together with trimethoprim. This hierarchy of choices is based on the outcome of several clinical trials that were done for prevention and treatment in the late 80's-early 90's. TMP/SMX was consistently more effective for prevention and treatment in a number of primary and secondary analyses of the data. For patients who can't take TMP/SMX for whatever reason, dapsone or dapsone+trimethoprim is a reasonable alternative.