In their recent article, Podzamczer and colleagues [1] analyzed the efficacy and safety of intermittent trimethoprim-sulfamethoxazole compared with those of dapsone-pyrimethamine for the simultaneous prophylaxis of Pneumocystis carinii pneumonia and toxoplasmic encephalitis in 230 patients infected with the human immunodeficiency virus (HIV). Of these patients, 131 were seropositive for Toxoplasma gondii. The main conclusion of this study was that thrice-weekly trimethoprim-sulfamethoxazole therapy (160 mg of trimethoprim plus 800 mg of sulfamethoxazole given twice daily) or dapsone (100 mg) plus pyrimethamine (50 mg) given twice weekly are effective and well-tolerated regimens for the simultaneous prophylaxis of these infections.

In 1991, we reported our results with low-dose, thrice-weekly trimethoprim-sulfamethoxazole, monthly aerosolized pentamidine, or weekly dapsone plus pyrimethamine for the prevention of P. carinii pneumonia and toxoplasmosis in 331 patients [2]. The rates of P. carinii pneumonia per year of observation were 5.6%, 3%, and 8.3% in the groups receiving pentamidine, trimethoprim-sulfamethoxazole, and dapsone plus pyrimethamine, respectively. All nine episodes of toxoplasmic encephalitis diagnosed during the trial developed among the 154 patients in whom IgG antibodies to T. gondii had been detected at study entry. None of the patients treated with trimethoprim-sulfamethoxazole developed a CT during the study (observation period, 21 patient-years). The rates in the remaining three groups of patients (receiving trimethoprim-sulfamethoxazole alone, pentamidine, and dapsone plus pyrimethamine) were greater than the rate of 4.3 per 100 patient-years seen with patients receiving aerosolized pentamidine alone.

Between December 1991 and October 1994, we recruited 294 patients who had CD4 counts less than 200 cells/mm³ and who were seropositive (IgG) for T. gondii. Patients were randomly assigned to receive trimethoprim (160 mg) plus sulfamethoxazole (800 mg) 3 days per week (157 patients, group 1) or dapsone (100 mg) plus pyrimethamine (25 mg) 2 days per week (137 patients, group 2). Patients were followed until July 1995 (mean follow-up, 20 ± 10 months). Forty-two patients (14.2%) were lost to follow-up. Eleven of 157 patients (7%) from group 1 and 12 of 137 patients (8.5%) from group 2 had side effects requiring a switch to pentamidine. Six patients (3.8%) from group 1 and 2 patients (1.5%) from group 2 developed toxoplasmic encephalitis. Four patients (2.6%) from group 1 and 8 patients (5.8%) from group 2 developed P. carinii pneumonia. The probability of developing encephalitis was 1.5 per 100 patients per year in group 2 and 2.3 per 100 patients per year in group 1. Forty-nine patients (16.7%) died during follow-up. The cumulative probability of survival was 82.5% at 3 years, with no differences between the two groups.

We agree with Podzamczer and colleagues [1] that intermittent trimethoprim-sulfamethoxazole or dapsone plus pyrimethamine regimens are useful in preventing toxoplasmosis and P. carinii pneumonia. Nevertheless, we can obtain the same efficacy and tolerance with lower doses of trimethoprim-sulfamethoxazole or dapsone plus pyrimethamine.