Cystoisosporiasis Medication

Updated: Apr 17, 2018
  • Author: Venkat R Minnaganti, MD, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
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Medication Summary

Cystoisosporiasis does not respond well to most antibiotics used to treat diarrhea. Oral trimethoprim-sulfamethoxazole (TMP-SMZ) is the drug of choice. In patients who are intolerant to sulfonamides, pyrimethamine with folinic acid may be given for 2-4 weeks. Patients with AIDS may require long-term maintenance therapy with TMP-SMZ for suppression of C belli. Alternatively, pyrimethamine with sulfadoxine may be given.

Anecdotal case reports document improvement with albendazole, bismuth subsalicylate, diclazuril, furazolidone, metronidazole, and quinacrine; however, clinical trials are lacking.



Class Summary

Therapy must be comprehensive and cover all likely pathogens in the context of this clinical setting.

TMP-SMZ is the drug of choice because it is the best-studied and most readily available agent. An alternative for long-term prophylaxis is pyrimethamine with sulfadiazine or sulfadoxine (either of which should be accompanied by folinic acid). Studies have proposed the veterinary agent diclazuril as a possible drug of choice if further studies confirm its use and safety.

Trimethoprim-sulfamethoxazole (Bactrim DS, Septra DS)

TMP-SMZ inhibits bacterial growth by inhibiting synthesis of dihydrofolic acid. It is the drug of choice and is curative in the immunocompetent host. It can be used for treatment and then ongoing prophylaxis in the immunocompromised host.

Pyrimethamine (Daraprim)

Pyrimethamine is a folic acid antagonist that selectively inhibits plasmodial dihydrofolate reductase. It is the second drug of choice and is particularly useful for those who cannot tolerate sulfonamides. It can also be used for prophylaxis when combined with sulfadiazine or sulfadoxine. Administer it with folinic acid to prevent hematologic toxicities.


Diclazuril is investigational in the United States. This benzene acetonitrile derivative is a veterinary antiparasitic that has shown good safety and efficacy in a small number of studies involving a small number of humans. Clinical trials have been completed for use in patients with AIDS and cryptosporidial-related diarrhea. 



Class Summary

Vitamins are used to correct folic acid deficiency resulting from use of folic acid antagonists.


A derivative of folic acid, which is used with folic acid antagonists such as sulfonamides and pyrimethamine.