Clinical Trials in Adults

The safety and efficacy of ZINPLAVA were investigated in two randomized, double-blind, placebo-controlled, multicenter, Phase 3 trials (Trial 1 and Trial 2) in patients receiving Standard of Care antibacterial drugs for treatment of CDI (SoC).

Randomization was stratified by SoC (metronidazole, vancomycin, or fidaxomicin) and hospitalization status (inpatient vs. outpatient) at the time of study entry.

Enrolled patients were 18 years of age or older and had a confirmed diagnosis of CDI, which was defined as diarrhea (passage of 3 or more loose bowel movements in 24 or fewer hours) and a positive stool test for toxigenic C. difficile from a stool sample collected no more than 7 days before study entry. Patients were excluded if surgery for CDI was planned, or if they had uncontrolled chronic diarrheal illness. Patients received a 10- to 14-day course of oral SoC and a single infusion of ZINPLAVA or placebo was administered during the course of SoC. Patients on oral vancomycin or oral fidaxomicin could have also received intravenous metronidazole. Choice of SoC was at the discretion of the health care provider. The day of the infusion of ZINPLAVA or placebo in relation to the start of SoC ranged from the day prior to the start of SoC to 14 days after the start of SoC with the median being day 3 of SoC.

In Trial 1, 403 patients were randomized to receive ZINPLAVA and 404 patients were randomized to receive placebo. In Trial 2, 407 subjects were randomized to receive ZINPLAVA and 399 patients were randomized to receive placebo. The Full Analysis Set (FAS) was a subset of all randomized subjects with exclusions for: (i) not receiving infusion of study medication; (ii) not having a positive local stool test for toxigenic C. difficile; (iii) not receiving protocol defined standard of care therapy within a 1 day window of the infusion. The baseline characteristics of the 1554 patients randomized to ZINPLAVA or placebo in the FAS were similar across treatment arms and in Trial 1 and Trial 2. The median age was 65 years, 85% were white, 57% were female, and 68% were inpatients. A similar proportion of patients received oral metronidazole (48%) or oral vancomycin (48%) and 4% of the patients received oral fidaxomicin as their SoC.

The following risk factors associated with a high risk of CDI recurrence or CDI-related adverse outcomes were present in the study population: 51% were ≥65 years of age, 39% received one or more systemic antibacterial drugs (during the 12-week follow-up period), 28% had one or more episodes of CDI within the six months prior to the episode under treatment (15% had two or more episodes prior to the episode under treatment), 21% were immunocompromised and 16% presented at study entry with clinically severe CDI (as defined by a Zar score of ≥21). A hypervirulent strain (ribotypes 027, 078 or 244) was isolated in 22% of patients who had a positive baseline culture, of which 87% (189 of 217 strains) were ribotype 027.

Patients were assessed for clinical cure of the presenting CDI episode, defined as no diarrhea for 2 consecutive days following the completion of a ≤14 day SoC regimen. Patients who achieved clinical cure were then assessed for recurrence of CDI through 12 weeks following administration of the infusion of ZINPLAVA or placebo. CDI recurrence was defined as the development of a new episode of diarrhea associated with a positive stool test for toxigenic C. difficile following clinical cure of the presenting CDI episode. Sustained clinical response was defined as clinical cure of the presenting CDI episode and no CDI recurrence through 12 weeks after infusion. Table 2 contains the results for Trial 1 and Trial 2.

In Trial 1, the clinical cure rate of the presenting CDI episode was lower in the ZINPLAVA arm as compared to the placebo arm and in Trial 2, the clinical cure rate was lower in the placebo arm compared to the ZINPLAVA arm. Patients in the ZINPLAVA and placebo arms who did not achieve clinical cure of the presenting CDI episode (no diarrhea for 2 consecutive days following the completion of a ≤14 day SoC regimen) received a mean of 18 to 19 days of SoC and had a mean of 4 additional days of diarrhea following completion of SoC. Additional analyses showed that by 3 weeks post study drug infusion the clinical cure rates of the presenting CDI episode were similar between treatment arms.

Efficacy results in patients at high risk for CDI recurrence (i.e., patients aged 65 years and older, with a history of CDI in the past 6 months, immunocompromised state, severe CDI at presentation, or C. difficile ribotype 027) were consistent with the efficacy results in the overall trial population in Trials 1 and 2.