Patients take nitazoxanide daily for 8 weeks with a dose escalation after the first 4 weeks. Patients return to the hospital for examinations every 2 weeks during the 8-week treatment period and 6-week follow-up. Nitazoxanide therapy is discontinued in patients showing a complete clinical and parasitologic response (therapeutic cure) after 8 weeks of treatment and in patients showing a therapeutic cure at two consecutive visits (Weeks 2 and 4 or Weeks 4 and 6). These patients undergo a physical examination including stool analysis for Cryptosporidium parvum oocysts and routine laboratory tests at Weeks 2, 4, and 6 after completion of nitazoxanide therapy. Patients who do not show a complete clinical and parasitologic response (therapeutic failure) after 8 weeks of treatment are allowed to remain on nitazoxanide therapy through the Open Label Compassionate Use of Nitazoxanide in Treatment of Cryptosporidiosis in AIDS Patients (UMD-95-009) protocol.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are HIV-positive.
• Have a CD4 cell count of 50 cells/mm3 or less.
• Have evidence of cryptosporidium infection in their stool sample within 10 days of study entry.
• Have watery stools at least three times a day at least 5 days a week for 21 days prior to enrollment.
• Are able to take medications by mouth.
• Are at least 13 years old (consent of parent or guardian required if under 18).
• Agree to use an effective method of birth control (such as condoms) during the study.

Exclusion Criteria

Patients will not be eligible if they:

• Have certain diseases or infections of the intestines.
• Have ever taken nitazoxanide.
• Have taken certain experimental drugs within 14 days of enrollment.
• Will need to take certain other medications during the study such as paromomycin, azithromycin, and clarithromycin.
• Have started a new anti-HIV therapy within 4 weeks of study entry or plan on starting one during the study.
• Are pregnant or breast-feeding.