To the Editor.
—Castellano and Nettleman1 suggest guidelines for conclusions about the prophylaxis of Pneumocystis carinii pneumonia (PCP) on the basis of a hypothetical situation analyzed by an extremely simple mathematical model.The simplicity of the Markov model, in fact, demanded that the authors ignore several documented clinical facts. As an example, the authors assumed that recurrence of PCP and risk of death remain constant during the study period and that the risks are equal among all patients in a defined "state." They also assumed that the risk of death is equal among those who have the acquired immunodeficiency syndrome (AIDS) for 2 months or 10 years. This does not reflect clinical reality.Because patients in such a state are considered equal in terms of risk, the model combines not only patients who have had AIDS for disparate lengths of time but also patients who have been receiving zidovudine
Gabin SJ. Prophylaxis Against Pneumocystis carinii Pneumonia. JAMA. 1992;267(13):1779. doi:10.1001/jama.1992.03480130091026