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RV521/78 µCi-RV521

Phase 2

Respiratory Syncytial Virus Infections | Small molecule | Infectious Disease |Pfizer, Inc.|Last Updated: Jul 31, 2025

Success Probability

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Market & Valuation

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Trial Design

RandomizedDouble-BlindPLACEBO_CONTROLLED

Total Trials3

Total Enrollment84

FDA Designations

No designations recorded

Clinical trial landscape

RV521/78 µCi-RV521 · 3 trials · 1 indication

Phase 2 1Phase 1 2

NCT03258502A Study to Learn About the Effects of Multiple Doses of Sisunatovir on People With Respiratory Syncytial Virus (RSV) InfectionRespiratory Syncytial Virus Infections

COMPLETED66 Analytics

PHASE2COMPLETED

A Study to Learn About the Effects of Multiple Doses of Sisunatovir on People With Respiratory Syncytial Virus (RSV) Infection

Respiratory Syncytial Virus Infections

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Study Endpoints

Primary Endpoints

Change in viral load

Baseline to study day 12

Tmax (Time of maximum observed concentration)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

Cmax (Maximum observed concentration)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

AUC0-inf (Area under the concentration-time curve (AUC) extrapolated to infinity)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

AUC0-last (AUC from the time of dosing to the time of the last measurable concentration)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

lambdaz (Rate constant associated with the terminal elimination phase)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

t1/2 (half-life of the terminal elimination phase)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

CL/F (Apparent clearance of the drug from plasma after oral administration)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

Vz/F (Volume of distribution associated with the terminal phase)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

CLR (renal clearance)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

Fe (fraction of administered drug excreted into urine)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

Ae0-t (cumulative amount of 14C excreted into urine from time 0 to the last sampling interval)

Day 1 (time 0) to Day 29

PK parameters of total radioactivity and RV521 following a single oral administration of \[ 14C\]-RV521 to healthy male subjects

Ae0-t (Cumulative amount of 14C excreted into urine and feces from time 0 to the last sampling interval (in units of mass-equivalents/g))

Day 1 (time 0) to Day 29

Mass balance parameters in urinary and fecal excretion of radioactivity

Aet (Amount of 14C excreted into urine and feces per sampling interval (in units of mass-equivalents/g))

Day 1 (time 0) to Day 29

Mass balance parameters in urinary and fecal excretion of radioactivity

Fet (Fraction of 14C excreted into urine and feces per sampling interval (in units of %))

Day 1 (time 0) to Day 29

Mass balance parameters in urinary and fecal excretion of radioactivity

Fe0-t (Cumulative fraction of 14C excreted into urine or feces from time 0)

Day 1 (time 0) to Day 29

Mass balance parameters in urinary and fecal excretion of radioactivity

14C associated with % of AUC of the total in plasma

Day 1 (time 0) to Day 29

Metabolite Profiling and Identification

14C associated with % of administered dose of the total in urine and feces

Day 1 (time 0) to Day 29

Metabolite Profiling and Identification

Time to maximum plasma concentration (tmax) for RV521

Baseline to study day 11

Terminal half life (t1/2) for RV521

Baseline to study day 11

Maximum observed plasma concentration (Cmax) for RV521

Baseline to study day 11

Area under the plasma concentration-time curve from time zero to last detectable plasma concentration (AUC0-t) for RV521

Baseline to study day 11

Area under the plasma concentration-time curve from time zero to infinity (AUC0-inf) for RV521

Baseline to study day 11

Secondary Endpoints

Spontaneously reported adverse events (AEs) during the Treatment Period

Day -1 to Day 29

Spontaneously reported serious AEs (SAEs) during the Treatment Period

Day -1 to Day 29

Use of concomitant medications

Day -1 to Day 29

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Study Design & Arms

AllocationRANDOMIZED

MaskingDOUBLE

ModelPARALLEL

PurposeTREATMENT

Treatment Arms

Arm	Type	Description
RV521	EXPERIMENTAL	RV521 drug substance in capsule for oral administration
Placebo	PLACEBO_COMPARATOR	Micro-crystalline cellulose in capsule for oral administration
200 mg RV521/78 µCi [ 14C]-RV521	EXPERIMENTAL	200 mg RV521/78 µCi \[ 14C\]-RV521

Interventions

Name	Type	Description
RV521	DRUG	RV521 drug in capsules
Placebo	DRUG	Placebo in capsules
200 mg RV521/78 µCi [ 14C]-RV521.	DRUG	200 mg RV521/78 µCi \[ 14C\]-RV521

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Eligibility Criteria

Age Range18 Years to 45 Years

SexALL

Healthy VolunteersYes

Study Sites1

Inclusion Criteria: * Age 18 to 45 years, inclusive * In good health with no history of major medical conditions * A total body weight ≥ 50 kg and a body mass index (BMI) of \>/=18kg/m2 and \</=30kg/m2 Exclusion Criteria: * Evidence of any clinically significant or currently active major medical ...

Countries:United KingdomUnited States

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Frequently asked questions about RV521/78 µCi-RV521

What is RV521 used for?

RV521 is an investigational small molecule being developed for the treatment of Respiratory Syncytial Virus (RSV) infections. It is currently in Phase 2 clinical development and has been studied in healthy volunteers to evaluate its effects on RSV infection.

Who makes RV521?

RV521 is being developed by Pfizer, Inc. (NYSE: PFE). The company has conducted clinical trials of the drug in the United Kingdom and the United States to evaluate its safety and pharmacokinetics.

What phase is RV521 in?

RV521 is in Phase 2 clinical development. It has completed three clinical trials, including a Phase 2 study and two Phase 1 studies, all of which have been completed. The drug is investigational and not yet approved.

What clinical trials is RV521 in?

RV521 has been studied in three completed clinical trials. NCT03258502 was a Phase 2 study of multiple doses in people with RSV infection. NCT04065698 and NCT05873764 were Phase 1 studies evaluating the pharmacokinetics and safety of the drug in healthy volunteers.

Is RV521 the same as sisunatovir?

Yes, RV521 is also known as sisunatovir. Clinical trial records for the drug use both names, with NCT03258502 and NCT05873764 referring to sisunatovir in their titles.