A Controlled Phase 2a Study to Evaluate the Efficacy of EDP-323 Against Respiratory Syncytial Virus Infection in a Virus Challenge Model

A Randomized, Phase 2a, Double-blind, Placebo-controlled Study to Evaluate the Safety, Pharmacokinetics and Antiviral Activity of Multiple Doses of Orally Administered EDP-323 Against Respiratory Syncytial Virus Infection in a Virus Challenge Model in Healthy Adults

A randomized, Phase 2a, double-blind, placebo-controlled study to evaluate the safety, pharmacokinetics and antiviral activity of multiple doses of orally administered EDP-323 in healthy subjects infected with RSV-A Memphis 37b. This study is designed to assess the antiviral effect of EDP-323 compared to a placebo control in the respiratory syncytial virus challenge model.

Study Overview

• Status: Completed
• Conditions: RSV Infection
• Intervention / Treatment: Drug: Placebo; Drug: EDP-323 Dose Regimen 1; Drug: EDP-323 Dose Regimen 2

• Study Type: Interventional
• Enrollment (Actual): 142
• Phase: Phase 2

Contacts and Locations

Study Locations

• United Kingdom
  • London, United Kingdom
    • hVIVO Services Limited

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• An informed consent document signed and dated by the subject.
• Age 18 to 55 years, inclusive.
• In good health with no history of major medical conditions.
• A total body weight ≥ 50 kg and Body Mass Index (BMI) ≥ 18 kg/m2 and ≤ 35kg/m2.

Exclusion Criteria:

• Pregnant or nursing females
• Acute or chronic medical illness
• History of, or currently active, symptoms or signs suggestive of upper or lower respiratory tract (URT or LRT) infection within 4 weeks prior to the first study visit.
• Abnormal lung function
• Positive for HIV, active hepatitis B or C test
• Nose or nasopharynx abnormalities
• Receipt of any investigational drug within 3 months prior to the planned date of viral challenge/first dose of study drug

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Double

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: EDP-323 Arm A; Subjects will take EDP-323 Dose 1 orally for 5 days	Drug: EDP-323 Dose Regimen 1; EDP-323 capsule
Experimental: EDP-323 Arm B; Subjects will take EDP-323 Dose 2 orally for 5 days	Drug: EDP-323 Dose Regimen 2; EDP-323 capsule
Placebo Comparator: Placebo Arm C; Subjects will take matching placebo orally for 5 days	Drug: Placebo; Placebo capsule

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Quantitative Reverse Transcription-polymerase Chain Reaction (qRT-PCR): RSV Area Under the Viral Load-time Curve (VL-AUC)	Measured by qRT-PCR in nasal samples.	Day 1 to Day 12

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
qRT-PCR: RSV Peak Viral Load (VLPEAK)	Measured by qRT-PCR in nasal samples.	Day 1 to Day 12
qRT-PCR: Time From the Assessment at the Time of the First Dose of IMP to RSV VLPEAK	Measured by qRT-PCR in nasal samples.	Day 1 to Day 12
qRT-PCR: Time From the Assessment at the Time of the First Dose of IMP to RSV Viral Load Negativity	The time from the assessment at the time of the first dose of IMP to qRT-viral load negativity was analyzed using the Kaplan-Meier method. Viral load negativity was reached at the first time when the viral load was undetectable (< lower limit of detection [LLOD]) by qRT-PCR, after which no further detectable assessment appeared. Measured by qRT-PCR in nasal samples.	Day 1 to Day 12
qRT-PCR: Time From the Assessment at the Time of the First Dose of IMP to First Negative Slope of RSV Viral Load	Time to first negative slope = time of the timepoint after which there are two consecutive declines in viral load - time of the nearest viral load assessment to the first dose of IMP. Measured by qRT-PCR in nasal samples.	Day 1 to Day 12
qRT-PCR: RSV Viral Load Clearance Rate - EDP-323 High Dose	Calculated as the slope of the RSV viral load over time from time of RSV VLPEAK to 1, 2, 3, and 4 days later. Estimates for fixed effects of a mixed linear model, modeling the viral load from peak up to the 4 following days, with time from VLPEAK, group and interaction between time and group as fixed effects and a random intercept within each participant. The model was a distinct analysis for the EDP-323 high dose and placebo groups where the estimates for both groups are model-dependent and impacted by the overall model. A negative slope indicated that the viral load decreased over time. Measured by qRT-PCR in nasal samples.	Up to Day 16
qRT-PCR: RSV Viral Load Clearance Rate - EDP-323 Low Dose	Calculated as the slope of the RSV viral load over time from time of RSV VLPEAK to 1, 2, 3, and 4 days later. Estimates for fixed effects of a mixed linear model, modeling the viral load from peak up to the 4 following days, with time from VLPEAK, group and interaction between time and group as fixed effects and a random intercept within each participant. The model was a distinct analysis for the EDP-323 low dose and placebo groups where the estimates for both groups are model-dependent and impacted by the overall model. A negative slope indicated that the viral load decreased over time. Measured by qRT-PCR in nasal samples.	Up to Day 16
Viral Culture: RSV VL-AUC	Measured by viral culture (plaque assay) in nasal samples.	Day 1 to Day 12
Viral Culture: RSV VLPEAK	Measured by viral culture (plaque assay) in nasal samples.	Day 1 to Day 12
Viral Culture: Time From the Assessment at the Time of the First Dose of IMP to RSV VLPEAK	Measured by viral culture (plaque assay) in nasal samples.	Day 1 to Day 12
Viral Culture: Time From the Assessment at the Time of the First Dose of IMP to RSV Viral Load Negativity	Measured by viral culture (plaque assay) in nasal samples.	Day 1 to Day 12
Viral Culture: Time From the Assessment at the Time of the First Dose of IMP to First Negative Slope of RSV Viral Load	Measured by viral culture (plaque assay) in nasal samples.	Day 1 to Day 12
Viral Culture: RSV Viral Load Clearance Rate	Calculated as the slope of the RSV viral load over time from time of RSV VLPEAK to 1, 2, 3, and 4 days later. Estimates for fixed effects of a mixed linear model, modeling the viral load from peak up to the 4 following days, with time from VLPEAK, group and interaction between time and group as fixed effects and a random intercept within each participant. A negative slope indicated that the viral load decreased over time. Measured by viral culture in nasal samples.	Up to Day 16
Area Under the Total Symptom Score (TSS)-Time Curve (TSS-AUC)	An individual TSS (10-items) was derived at each assessment of the diary card as the sum of the scores given to the 10 following symptoms on that symptom score card, giving a score between 0 and 3: Runny nose; Stuffy nose; Sneezing; Sore throat; Earache; Malaise/Tiredness; Headache; Muscle and/or Joint Ache; Cough; Shortness of breath TSS ranged from 0 to 30 with higher TSS indicating a higher disease burden and thus a worse outcome. The calculation of the TSS-AUC was performed on the TSS measured 3 times a day using the trapezoidal summation rule based on actual time intervals in hours.	Day 1 to Day 12
Peak TSS	Defined as the highest recorded value of TSS. An individual TSS (10-items) was derived at each assessment of the diary card as the sum of the scores given to the 10 following symptoms on that symptom score card, giving a score between 0 and 3: Runny nose; Stuffy nose; Sneezing; Sore throat; Earache; Malaise/Tiredness; Headache; Muscle and/or Joint Ache; Cough; Shortness of breath TSS ranged from 0 to 30 with higher TSS indicating a higher disease burden and thus a worse outcome.	Day 1 to Day 12
Time to Peak TSS	Time to peak TSS = time of peak TSS - time of the nearest TSS assessment to the first dose of IMP. An individual TSS (10-items) was derived at each assessment of the diary card as the sum of the scores given to the 10 following symptoms on that symptom score card, giving a score between 0 and 3: Runny nose; Stuffy nose; Sneezing; Sore throat; Earache; Malaise/Tiredness; Headache; Muscle and/or Joint Ache; Cough; Shortness of breath TSS ranged from 0 to 30 with higher TSS indicating a higher disease burden and thus a worse outcome.	Day 1 to Day 12
Time to Resolution From Peak TSS	Time to resolution from peak TSS = time of the first 24-hour symptom-free time point - time of peak TSS. An individual TSS (10-items) was derived at each assessment of the diary card as the sum of the scores given to the 10 following symptoms on that symptom score card, giving a score between 0 and 3: Runny nose; Stuffy nose; Sneezing; Sore throat; Earache; Malaise/Tiredness; Headache; Muscle and/or Joint Ache; Cough; Shortness of breath TSS ranged from 0 to 30 with higher TSS indicating a higher disease burden and thus a worse outcome.	Day 1 to Day 12
Total Weight of Nasal Discharge (Mucus) Produced	Each participant was given pre-weighed packets of paper tissues. Participants were asked to place single tissues used for nose blowing or sneezing into a specified collection bag (for that participant only).	Day 1 to Day 12
Total Number of Tissues Used	Each participant was given pre-weighed packets of paper tissues. Participants were asked to place single tissues used for nose blowing or sneezing into a specified collection bag (for that participant only).	Day 1 to Day 12
Maximum Plasma Concentration (Cmax)	Plasma pharmacokinetic (PK) parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The plasma PK parameters were estimated from the concentration-time profiles. In estimating the PK parameters, below the limit of quantification (BQL) values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	First Dose: Day 1 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, and 15 hours post-dose) and Day 2 pre-dose; Last Dose: Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Time to Cmax (Tmax)	Plasma PK parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The plasma PK parameters were estimated from the concentration-time profiles. In estimating the PK parameters, BQL values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	First Dose: Day 1 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, and 15 hours post-dose) and Day 2 pre-dose; Last Dose: Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Terminal Half-life (t1/2)	Plasma PK parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The plasma PK parameters were estimated from the concentration-time profiles. In estimating the PK parameters, BQL values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	Day 1 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, and 15 hours post-dose), Day 2 pre-dose, Day 3 pre-dose, Day 4 pre-dose, Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Apparent Systemic Clearance at Steady-state (CLss/F)	Plasma PK parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The plasma PK parameters were estimated from the concentration-time profiles. In estimating the PK parameters, BQL values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	Day 1 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, and 15 hours post-dose), Day 2 pre-dose, Day 3 pre-dose, Day 4 pre-dose, Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Terminal Elimination Rate Constant (λz)	Plasma PK parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The plasma PK parameters were estimated from the concentration-time profiles. In estimating the PK parameters, BQL values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	Day 1 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, and 15 hours post-dose), Day 2 pre-dose, Day 3 pre-dose, Day 4 pre-dose, Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Apparent Volume of Distribution at Steady-state (Vss/F)	Plasma PK parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The plasma PK parameters were estimated from the concentration-time profiles. In estimating the PK parameters, BQL values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	Day 1 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, and 15 hours post-dose), Day 2 pre-dose, Day 3 pre-dose, Day 4 pre-dose, Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Plasma Concentration at 12 Hours (C12h) and 24 Hours (C24h)	In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	First Dose: Day 1, 12 and 24 hours post-dose; Last Dose: Day 5, 12 and 24 hours post-dose
Area Under the Concentration-time Curve From Time 0 to Time of Last Quantifiable Concentration (AUC0-last)	Plasma PK parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The AUCs were calculated using linear up/log down method. In estimating the PK parameters, BQL values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	First Dose: Day 1 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, and 15 hours post-dose) and Day 2 pre-dose; Last Dose: Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Area Under the Concentration-time Curve Over the Dosing Interval (AUC0-tau)	Plasma PK parameters for EDP-323 and metabolites (EP-038725 and EP-039082) were estimated using non-compartmental methods. The AUCs were calculated using linear up/log down method. In estimating the PK parameters, BQL values were set to zero. Actual sampling times, rather than scheduled sampling times, were used in all computations involving sampling times. If the actual time or dose time was missing, the scheduled time could be substituted in order to calculate the PK parameter. In case of an actual sampling time deviating by >20% from the scheduled (nominal) time, this plasma concentration was excluded from descriptive statistics in the plasma concentration-time table.	Last Dose: Day 5 (pre-dose, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 30, 36, 48, 60, and 72 hours post-dose)
Number of Participants With Adverse Events (AEs) up to Discharge	An AE was defined as any untoward medical occurrence in clinical study participants administered a pharmaceutical (investigational or non-investigation) product. An AE does not necessarily have a causal relationship with the study intervention. A serious AE (SAE) was defined as any untoward medical occurrence that, at any dose: Resulted in death; Was life threatening; Required inpatient hospitalization or prolongation of existing hospitalization; Resulted in persistent disability/incapacity; Was a congenital anomaly/birth defect; Was an important medical event	Day -2 to Day 12
Number of Participants With Treatment-emergent Adverse Events	An AE was defined as any untoward medical occurrence in clinical study participants administered a pharmaceutical (investigational or non-investigation) product. An AE does not necessarily have a causal relationship with the study intervention. An SAE was defined as any untoward medical occurrence that, at any dose: Resulted in death; Was life threatening; Required inpatient hospitalization or prolongation of existing hospitalization; Resulted in persistent disability/incapacity; Was a congenital anomaly/birth defect; Was an important medical event	Day 1 to Day 28

Collaborators and Investigators

• Sponsor: Enanta Pharmaceuticals, Inc
• Collaborators: hVIVO Services Limited
• Investigators: Study Director: Enanta Pharmaceuticals, Inc, Enanta Pharmaceuticals, Inc

Study record dates

Study Major Dates

• Study Start (Actual): November 20, 2023
• Primary Completion (Actual): June 17, 2024
• Study Completion (Actual): July 12, 2024

Study Registration Dates

• First Submitted: November 27, 2023
• First Submitted That Met QC Criteria: December 6, 2023
• First Posted (Actual): December 14, 2023

Study Record Updates

• Last Update Posted (Estimated): October 7, 2025
• Last Update Submitted That Met QC Criteria: September 18, 2025
• Last Verified: September 1, 2025

More Information

Terms related to this study

• Keywords: RSV; antiviral; challenge study; RSV-A Memphis 37b
• Additional Relevant MeSH Terms: Infections; RNA Virus Infections; Virus Diseases; Pneumovirus Infections; Paramyxoviridae Infections; Mononegavirales Infections; Respiratory Syncytial Virus Infections
• Other Study ID Numbers: EDP 323-101

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No