Resources for Health Professionals


Trimethoprim-sulfamethoxazole (TMP-SMX), sold under the trade names Bactrim*, Septra*, and Cotrim*, is the medication of choice for Cystoisospora infection. The typical treatment regimen for adults is TMP 160 mg plus SMX 800 mg (one double-strength tablet), orally, twice a day, for 7 to 10 days.

Expert consultation is recommended if the patient is immunosuppressed, for example, has AIDS. Such patients may need to be treated longer and/or with higher daily doses. This is an example of an alternative regimen of TMP-SMX for adults: one double-strength tablet of TMP-SMX, orally, four times a day, for up to 3 or 4 weeks. Patients with AIDS also may need maintenance therapy (secondary prophylaxis) with TMP-SMX to prevent recurrence of symptomatic infection.

Only limited data are available regarding potential alternatives to TMP-SMX. Patients who are allergic to (or are intolerant of) TMP-SMX usually are treated with pyrimethamine. For adults, the typical daily dose of pyrimethamine is in the range of 50 to 75 mg. This daily dose is given orally, either once a day or divided into 2 separate doses. For example, 50 mg can be given in one dose, or 25 mg can be given twice a day. Pyrimethamine can suppress the bone marrow. To help prevent this, patients treated with pyrimethamine also take leucovorin, orally, in a daily dose in the range of 10 to 25 mg. Folinic acid is another name for leucovorin.

Ciprofloxacin is a second-line alternative. It is less effective than TMP-SMX but might have some activity against Cystoisospora. For adults, the treatment regimen is 500 mg, orally, twice a day, for 7 days.* Trimethoprim–sulfamethoxazole (TMP–SMX) is available for human use in the United States.

* Ciprofloxacin is available for human use in the United States.

* Use of trade names is for identification only and does not imply endorsement by the Public Health Service or by the U.S. Department of Health and Human Services.


This information is provided as an informational resource for licensed health care providers as guidance only. It is not intended as a substitute for professional judgment.



Page last reviewed: May 21, 2020