The efficacy of MYTESI was evaluated in a randomized, double-blind, placebo-controlled (one month) and placebo-free (five month), multi-center study. The study enrolled 374 HIV-positive patients on stable anti-retroviral therapy with a history of diarrhea for one month or more. Diarrhea was defined as either persistently loose stools despite regular use of anti-diarrheal medication (e.g., loperamide, diphenoxylate, and bismuth subsalicylate) or one or more watery bowel movements per day without regular anti-diarrheal medicine use.

Patients were excluded if they had a positive gastrointestinal biopsy, gastrointestinal culture, or stool test for multiple bacteria (Salmonella, Shigella, Campylobacter, Yersinia, Mycobacterium), bacterial toxin (Clostridium difficile), ova and parasites (Giardia, Entamoeba, Isospora, Cyclospora, Cryptosporidium, Microsporidium), or viruses (Cytomegalovirus). Patients were also excluded if they had a history of ulcerative colitis, Crohn’s disease, celiac sprue (gluten-enteropathy), chronic pancreatitis, malabsorption, or any other gastrointestinal disease associated with diarrhea. 

The study had a two-stage adaptive design. In both stages, patients received placebo for 10 days (screening period) followed by randomization to crofelemer or placebo for 31 days of treatment (double-blind period). Only patients with 1 or more watery bowel movements per day on at least 5 of the last 7 days in the screening period were randomized to the double-blind period. Each stage enrolled patients separately; the dose for the second stage was selected based on an interim analysis of data from the first stage. In the first stage, patients were randomized 1:1:1:1 to one of three crofelemer dosage regimens (125 mg twice daily, or one of two higher dosage regimens) or placebo. In the second stage, patients were randomized 1:1 to MYTESI 125 mg twice daily or placebo. The efficacy analysis was based on results from the double-blind portion of both stages.

Each study stage also had a five month period (placebo-free period) that followed the double-blind period. Patients treated with MYTESI continued the same dose in the placebo-free period. In the first stage, patients that received placebo were re-randomized 1:1:1 to one of the three crofelemer dosage regimens (125 mg twice daily, or one of the two higher dosage regimens) in the placebo-free period. In the second stage, patients that received placebo were treated with MYTESI 125 mg twice daily in the placebo-free period.

The median time since diagnosis of HIV was 12 years. The percentage of patients with a CD4 cell count of less than 404 was 39%. The percentage of patients with a HIV viral load greater than or equal to 1000, 400 to 999, and less than 400 HIV copies/mL was 7%, 3%, and 9%, respectively; the remainder had a viral load that was not detectable. The median time since diarrhea started was 4 years. The median number of daily watery bowel movements was 2.5 per day. 

Most patients were male (85%). The percentage of patients that were Caucasian was 46%; the percentage of patients that were African-American was 32%. The median age was 45 years with a range of 21 to 68 years.

In the double-blind period of the study, 136 patients received MYTESI 125 mg twice daily, 101 patients received one of the two higher dosage regimens and 138 patients received placebo. The percentages of patients that completed the double-blind period were 92% in the MYTESI 125 mg group and 94% in the placebo arm.

Most patients received concomitant protease inhibitors during the double-blind period (Table 2). The most frequently used anti-retroviral therapies in the MYTESI 125 mg and placebo groups were tenofovir/emtricitabine, ritonavir, and lopinavir/ritonavir.

The primary efficacy endpoint was the proportion of patients with a clinical response, defined as less than or equal to 2 watery bowel movements per week during at least 2 of the 4 weeks of the placebo-controlled phase. Patients who received concomitant anti-diarrheal medications or opiates were counted as clinical non-responders.

A significantly larger proportion of patients in the MYTESI 125 mg twice daily group experienced clinical response compared with patients in the placebo group (18% vs. 8%, 1–sided p < 0.01). In the randomized clinical study, examination of duration of diarrhea, baseline number of daily watery bowel movements, use of protease inhibitors, CD4 cell count and age subgroups did not identify differences in the consistency of the crofelemer treatment effect among these subgroups. There were too few female patients and patients with an HIV viral load > 400 copies/mL to adequately assess differences in effects in these populations. Among race subgroups, there were no differences in the consistency of the crofelemer treatment effect except for the subgroup of African-Americans; crofelemer was less effective in African-Americans than non-African-Americans.

Although the CD4 cell count and HIV viral load did not appear to change over the one month placebo-controlled period, the clinical significance of this finding is unknown because of the short duration of the placebo-controlled period.

Of the 24 clinical responders to MYTESI 125 mg twice daily, 22 entered the placebo-free period; 16 were responding at the end of month 3, and 14 were responding at the end of month 5.