Pneumocystis carinii Pneumonia: Using Simulation Modeling to Inform Clinical Guidelines.

Background: Human immunodeficiency virus (HIV)infected patients receiving highly active antiretroviral therapy (HAART) have experienced a dramatic decrease in Pneumocystis carinii pneumonia (PCP), necessitating reassessment of clinical guidelines for prophylaxis. Methods: A simulation model of HIV infection was used to estimate the lifetime costs and quality-adjusted life expectancy (QALE) for alternative CD4 cell count criteria for stopping primary PCP prophylaxis in patients with CD4 cell count increases receiving HAART and alternative agents for second-line PCP prophylaxis in those intolerant of trimethoprim-sulfamethoxazole (TMP/SMX). The target population was a cohort of HIV-infected patients in the United States with initial CD4 cell counts of 350/µL who began PCP prophylaxis after their first measured CD4 lymphocyte count less than 200/µL. Data were from randomized controlled trials and other published literature. Results: For patients with CD4 cell count increases during HAART, waiting to stop prophylaxis until the first observed CD4 cell count was greater than 300/µL prevented 9 additional cases per 1000 patients and cost $9400 per quality-adjusted life year (QALY) gained compared with stopping prophylaxis at 200/µL. For patients intolerant of TMP/SMX, using dapsone increased QALE by 2.7 months and cost $4500 per QALY compared with no prophylaxis. Using atovaquone rather than dapsone provided only 3 days of additional QALE and cost more than $1.5 million per QALY. Conclusions: Delaying discontinuation of PCP prophylaxis until the first observed CD4 cell count greater than 300/µL is cost-effective and provides an explicit "PCP prophylaxis stopping criterion." In TMP/SMX-intolerant patients, dapsone is more cost-effective than atovaquone. [ABSTRACT FROM AUTHOR]