In the double-blind portion of study, patients receive albendazole or placebo for 28 days; in the open-label portion of study, patients receive albendazole for 62 days.

Inclusion Criteria

Concurrent Medication:

Required:

• If coincident enteric pathogens that are not eradicable (i.e., Mycobacterium avium complex) are detected, they should be treated appropriately and the patient must be on a stable regimen of therapy for at least two weeks.

Allowed:

• Patients taking antidiarrheal medications must be on a stable regimen for at least seven days prior to randomization.
• Patients taking other concomitant medications, including antiretrovirals, must be on a stable regimen for two weeks prior to randomization.

Patients must have:

• HIV positive status. Written documentation (for example, patient's chart) of HIV diagnosis is acceptable in lieu of repeat testing. Confirmation by Western blot is not necessary.
• Biopsy-proven microsporidiosis of the fourth portion of the duodenum or proximal jejunum within 90 days before randomization.
• Average of > 3 liquid bowel movements per day over 7 consecutive days immediately prior to randomization, with an average volume > 500 ml per day over three or more consecutive days immediately prior to randomization, as documented by data collected in a daily diary. NOTE:
• Patients receiving antidiarrheal therapy must meet these criteria despite such therapy.
• History of an average of > 3 liquid bowel movements per day for three additional weeks immediately preceding the 7-day period described above (for a total of four weeks), as documented in the patient's chart.

Exclusion Criteria

Co-existing Condition:

Patients with the following symptoms or conditions are excluded:

• Grade 4 neutropenia.
• Decompensated liver disease.
• Positive toxin analysis for C. difficile.
• Positive microscopic examination for Giardia lamblia, Entamoeba histolytica, and Isospora belli.
• Positive on culture for Shigella, Salmonella, Yersinia and Campylobacter.
• Positive fluorescent antibody test for Cryptosporidium.
• Evidence of CMV on small bowel biopsy, flexible sigmoidoscopic or colonoscopic biopsies within 90 days of randomization.
• Any other condition that, in the opinion of the investigator, makes the patient unsuitable for study entry.

Patients with the following prior conditions are excluded:

Hypersensitivity to albendazole.

Prior Medication:

Excluded:

• Use of potential antiprotozoal drugs, e.g., mebendazole or metronidazole, within one week prior to enrollment.
• Receipt of albendazole during the one month prior to enrollment.