Pneumocystis Prophylaxis: Study Suggests Lower Bactrim Dose

A study of hospital records, published February 23, 1991, in The Lancet, has suggested that low-dose co-trimoxazole (also called Bactrim, Septra, sulfamethoxazole-trimethoprim, etc. -- there are many different names for this drug) was more effective than aerosol pentamidine for preventing pneumocystis, may also help prevent toxoplasmosis, and had fewer side effects than the larger Bactrim doses used in other studies to prevent pneumocystis. And the cost of this form of pneumocystis prophylaxis, when generic versions of the drug are used, is about a hundred times less than the cost of aerosol pentamidine; the drug can cost about $10 per year, making this therapy potentially available to everyone.

The patients studied were members of Kaiser Permanente Medical Care Program in Los Angeles. Since Kaiser patients usually get all their care from Kaiser clinics and hospitals, and obtain their prescriptions from Kaiser pharmacies, uniform records of visits and prescriptions were available. 116 patients met all the criteria for this study: consecutive prescriptions for co-trimoxazole between December 1986 and June 1988, symptoms of immune deficiency, a diagnosis of AIDS or ARC, and either previous pneumocystis and/or T-helper count under 200. All records were reviewed until June 1990, or until the patients died; no one was lost to followup. The co-trimoxazole dose used by these 116 patients was one DS (double strength) tablet every Monday, Wednesday, and Friday.

No patient had pneumocystis while on this treatment. Of the 116 patients in the study, 71 had previously had pneumocystis, and they were followed on the prophylaxis for an average of 18.5 months. Those who had not had pneumocystis previously were followed for an average of 24.2 months. By contrast, without prophylaxis, half of the patients who have had pneumocystis would be expected to relapse within eight months, according to published data from other studies; and more than half of symptomatic patients with T-helper counts less than 200, but who have never had pneumocystis, would probably develop the disease within 24 months.

These results were better than those with aerosol pentamidine. The same Kaiser center found that 10 percent of patients who had previously had pneumocystis relapsed within one year, despite 300 mg of aerosolized pentamidine once per month.

Also, there were no cases of toxoplasmosis among the 116 patients treated with the low-dose co-trimoxazole. There were cases of the disease among those treated with aerosol pentamidine (which could have no effect on toxoplasmosis, because very little of the drug leaves the lungs). However, there were not enough cases to show for sure that co-trimoxazole was preventing the disease; the fact that no one developed toxoplasmosis might have been a result of the therapy, or it might have been coincidence.

Side effects believed due to co-trimoxazole -- especially rash, fever, and nausea -- occurred in 28 percent of the 116 patients. But only in nine percent (of the 116) were they severe enough to require permanently stopping the drug. (In some other cases, the co-trimoxazole was stopped for seven to ten days, and then could be restarted.) Side effects almost always began within the first month if they occurred at all. In no case were they life-threatening or otherwise very severe.