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Cystoisosporiasis Medication

  • Author: Venkat R Minnaganti, MD, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
Updated: Dec 02, 2015

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.

Contributor Information and Disclosures

Venkat R Minnaganti, MD, FACP Consulting Staff, Department of Medicine, Winthrop University Hospital; Clinical Instructor, Department of Internal Medicine, Division of Infectious Disease, SUNY Stony Brook University School of Medicine

Venkat R Minnaganti, MD, FACP is a member of the following medical societies: All India Ophthalmological Society, American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

John W King, MD Professor of Medicine, Chief, Section of Infectious Diseases, Director, Viral Therapeutics Clinics for Hepatitis, Louisiana State University Health Sciences Center; Consultant in Infectious Diseases, Overton Brooks Veterans Affairs Medical Center

John W King, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Federation for Medical Research, Association of Subspecialty Professors, American Society for Microbiology, Infectious Diseases Society of America, Sigma Xi

Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

Klaus-Dieter Lessnau, MD, FCCP Clinical Associate Professor of Medicine, New York University School of Medicine; Medical Director, Pulmonary Physiology Laboratory; Director of Research in Pulmonary Medicine, Department of Medicine, Section of Pulmonary Medicine, Lenox Hill Hospital

Klaus-Dieter Lessnau, MD, FCCP is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Medical Association, American Thoracic Society, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Glenn Fennelly, MD, MPH Director, Division of Infectious Diseases, Lewis M Fraad Department of Pediatrics, Jacobi Medical Center; Clinical Associate Professor of Pediatrics, Albert Einstein College of Medicine

Glenn Fennelly, MD, MPH is a member of the following medical societies: Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

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Oocyst of Cystoisospora belli with 2 sporoblasts. From the Image Library, Division of Parasitic Diseases at the National Center for Infectious Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia.
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