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Trimethoprim-sulfamethoxazole continues to be the best choice for preventing PCP in AIDS patients

Pneumocystis carinii pneumonia (PCP) remains one of the most common life-threatening complications of AIDS. Of the three regimens most often used for PCP prophylaxis, trimethoprim-sulfamethoxazole (TMP-SMX) is superior to prevent initial and second-time PCP (primary and secondary prophylaxis) and most cost-effective for secondary prophylaxis, according to two studies supported in part by the Agency for Health Care Policy and Research (HS07782 and HS06694).

A meta-analysis of 35 randomized trials (conducted between 1991 and 1995 and involving 6,583 patients) led by Joseph Lau, M.D., of New England Medical Center Hospitals, compared three different treatment regimens: TMP-SMX, dapsone, (both are oral medications), and aerosolized pentamidine (AP) with each other or placebo. AP was well tolerated regardless of the dose used (usual recommended dose is 300 mg per month via nebulizer), but prophylaxis failure might be halved if the dose were doubled. Oral medications were five times more likely than AP to be discontinued because of toxic reactions.

Regardless of dose, TMP-SMX was almost universally effective for patients who tolerated it. The risk of discontinuation because of side effects decreased 43 percent if one double-strength tablet (160 mg TMP, 800 mg SMX) was given three times per week instead of daily (usual recommended dose). For dapsone, in 100 patients given 100 mg per day instead of twice per week for 1 year (primary prophylaxis), 7 fewer patients would develop PCP, but 17 more would have significant toxic reactions.

The second study shows that TMP-SMX also is more cost-effective than AP for preventing recurring PCP. Investigators at Dartmouth Medical School developed a model of secondary PCP prophylaxis based on the medical literature and then used efficacy and toxicity data from a controlled clinical trial to validate the model. They compared three clinical strategies in a hypothetical group of patients who had completed 21 days of therapy for PCP: no prophylaxis (control group), prophylaxis with TMP-SMX (one double-strength tablet per day), and prophylaxis with AP (300 mg per month).

In the literature-based model, yearly prophylaxis costs for TMP-SMX and AP were $468 and $1,577, respectively. Assuming equal efficacy for the two agents, the incremental cost-effectiveness ratio for TMP-SMX was $350 compared with no prophylaxis; for AP it was $110,880 compared with TMP-SMX, since AP was associated with only a minimal increase in life expectancy and a substantial increase in cost. Data from the randomized trial indicated annual costs of $656 per person for TMP-SMX and $1,573 per person for AP. This translates into annual savings of over $17.4 million for the 19,039 patients newly diagnosed as having PCP in 1993, if they were started on TMP-SMX rather than AP to prevent reinfection with PCP.

More details of the first study are in "Meta-analysis of the relative efficacy and toxicity of Pneumocystis carinii prophylactic regimens," by John P. Ioannidis, M.D., Joseph C. Cappeleri, Ph.D., M.P.H., Paul R. Skolnik, M.D., and others, in the January 22, 1996 Archives of Internal Medicine 156, pp. 177-188.

For the second study, see "Validating literature-based models with direct clinical trial results," by Kenneth A Freedberg, M.D., M.Sc., W. David Hardy, M.D., Robert S. Holzman, M.D., and others, in the January 1996 issue of Medical Decision Making 16(1), pp. 29-35.

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