Paxlovid for Treatment of Long Covid (STOP-PASC)
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ClinicalTrials.gov Identifier: NCT05576662 |
Recruitment Status :
Active, not recruiting
First Posted : October 12, 2022
Last Update Posted : August 21, 2023
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The purpose of this study is to compare whether being treated with Paxlovid (nirmatrelvir plus ritonavir) for 15 days works better than being treated with placebo (plus ritonavir) to reduce severe symptoms of Long Covid (the placebo does not have any active drug).
Participants will have 5 planned visits to the study clinic over 15 weeks and will take the drug (or placebo) for the first 15 days.
This study uses the term post-acute sequelae of SARS-CoV-2 (PASC), which is another name for "Long Covid."
Condition or disease | Intervention/treatment | Phase |
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Post-acute Sequelae of SARS-CoV-2 Infection Long COVID | Drug: Nirmatrelvir Drug: Placebo Drug: Ritonavir | Phase 2 |
Study Type : | Interventional (Clinical Trial) |
Actual Enrollment : | 168 participants |
Allocation: | Randomized |
Intervention Model: | Parallel Assignment |
Masking: | Double (Participant, Investigator) |
Primary Purpose: | Treatment |
Official Title: | Selective Trial Of Paxlovid for PASC (STOP-PASC): Randomized Double-Blind Placebo-Controlled Pilot Trial of Paxlovid for the Treatment of PASC |
Actual Study Start Date : | November 8, 2022 |
Actual Primary Completion Date : | August 14, 2023 |
Estimated Study Completion Date : | September 2023 |

Arm | Intervention/treatment |
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Experimental: Nirmatrelvir plus ritonavir
Participants receive nirmatrelvir plus ritonavir (Paxlovid) for 15 days, and attend follow-up visits through week 15.
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Drug: Nirmatrelvir
Two 150 mg tablets taken by mouth every 12 hours Drug: Ritonavir One 100 mg capsule taken by mouth every 12 hours |
Placebo Comparator: Placebo plus ritonavir
Participants receive placebo to match nirmatrelvir plus ritonavir for 15 days, and attend follow-up visits through week 15.
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Drug: Placebo
Two tablets containing placebo matching nirmatrelvir taken by mouth every 12 hours Drug: Ritonavir One 100 mg capsule taken by mouth every 12 hours |
- Core Symptoms Severity Scale Score [ Time Frame: Week 10 ]This measure will evaluate whether there is a difference between treatment with Paxlovid versus placebo on any of the 6 core symptoms of PASC at week 10 (adjusting for patients' baseline levels). Each symptom (fatigue, brain fog, dyspnea, body aches, gastrointestinal symptoms, cardiovascular symptoms) is assessed on a 4-point Likert scale (range: 0 to 3; 0 = no symptoms; 1 = mild symptoms; 2 = moderate symptoms; 3 = severe symptoms).
- Core Symptoms Severity Scale Score [ Time Frame: Day 15 ]This measure will evaluate whether there is a difference between treatment with Paxlovid versus placebo on any of the 6 core symptoms of PASC at day 15 (adjusting for patients' baseline levels). Each symptom (fatigue, brain fog, dyspnea, body aches, gastrointestinal symptoms, cardiovascular symptoms) is assessed on a 4-point Likert scale (range: 0 to 3; 0 = no symptoms; 1 = mild symptoms; 2 = moderate symptoms; 3 = severe symptoms).
- Number of participants reporting relief of at least one core symptom for 2 weeks [ Time Frame: Baseline through week 10, assessed at week 10 ]Relief defined as reduction of severity from moderate to none, or severe to mild/none (≥ 2-point Likert score change). Likert score range: 0 to 3; 0 = no symptoms; 1 = mild symptoms; 2 = moderate symptoms; 3 = severe symptoms.
- Number of participants with overall alleviation for 2 weeks [ Time Frame: Baseline through week 10, assessed at week 10 ]
Overall alleviation defined as both:
- Any core symptom(s) that are none/mild (Likert 0 or 1) at baseline are none at 10 weeks, and
- Any core symptom(s) that are moderate/severe (Likert 2 or 3) at baseline are none/mild at 10 weeks.
Likert score range: 0 to 3; 0 = no symptoms; 1 = mild symptoms; 2 = moderate symptoms; 3 = severe symptoms.
- Severity of the most bothersome symptom [ Time Frame: Assessed at weeks 5, 10, and 15 ]Severity assessed on a 4-point Likert scale (range: 0 to 3; 0 = no symptoms; 1 = mild symptoms; 2 = moderate symptoms; 3 = severe symptoms).
- Time to relief of the 6 core symptoms [ Time Frame: Up to 15 weeks ]Relief defined as reduction of severity from moderate to none, or severe to mild/none (≥ 2-point Likert score change). Likert score range: 0 to 3; 0 = no symptoms; 1 = mild symptoms; 2 = moderate symptoms; 3 = severe symptoms.
- Change in PROMIS Physical Function Score [ Time Frame: Baseline and week 10 ]The PROMIS-Physical Function Short Form assesses difficulty level performing activities of daily living such as doing chores, climbing stairs, walking, and running errands.
- Change in PROMIS Fatigue Score [ Time Frame: Baseline and week 10 ]The PROMIS Fatigue Score assesses level of fatigue and its interference on daily activities.
- Change in PROMIS Dyspnea-Severity Score [ Time Frame: Baseline and week 10 ]The PROMIS-Fatigue Dyspnea-Severity Short Form assesses shortness of breath and its interference on daily activities.
- Change in PROMIS Cognitive Function Abilities Score [ Time Frame: Baseline and week 10 ]The PROMIS-Cognitive Function Abilities Short Form assesses brain fog and its interference on daily activities.
- Change in orthostatic vitals test [ Time Frame: Baseline and week 10 ]This outcome measures the difference in seated versus standing blood pressure.
- Change in 1-minute sit-to-stand test [ Time Frame: Baseline and week 10 ]Number of times participant is able to go from sitting (in an armless chair) to standing in 1 minute.
- Patient Global Impression of Severity (PGIS) scale score [ Time Frame: Weeks 5, 10, and 15 ]Change in health status rated from 1 to 6. 1 = not present; 2 = very mild; 3 = mild; 4 = moderate; 5 = severe; 6 = extremely severe.
- Patient Global Impression of Change (PGIC) scale score [ Time Frame: Baseline and weeks 5, 10, and 15 ]Change in health status rated from 1 to 7. 1 = very much improved; 2 = much improved; 3 = minimally improved; 4 = no change; 5 = minimally worse; 6 = much worse; 7 = very much worse.

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Ages Eligible for Study: | 18 Years and older (Adult, Older Adult) |
Sexes Eligible for Study: | All |
Accepts Healthy Volunteers: | No |
Inclusion Criteria:
- Normal or near-normal kidney function
- History of confirmed COVID-19 infection that preceded the post-COVID symptoms
- Post-COVID-19 symptoms persisting greater than three months
- At least 2 post-COVID symptoms of moderate or severe intensity (fatigue, brain fog, shortness of breath, body aches, gastrointestinal symptoms, or cardiovascular symptoms)
- Willing to report all vaccinations
- Women of childbearing potential or men whose partners may become pregnant must use acceptable method of contraception during the treatment period and for 28 days after the last dose of the study drug
- Willing and able to adhere to study procedures and available for the duration of the study
Exclusion Criteria:
- Suspected or confirmed pregnancy or breastfeeding
- Severe liver disease
- Prior use of study drug or other COVID treatment within 30 days
- Hypersensitivity or other contraindication to any components of the study drug
- Current or expected use of any medication dependent on or inducer of CYP3A4
- Current or expected use of supplements or herbs (unless medically necessary) that cannot be temporarily held (period as determined necessary by investigators)
- HIV infection with viral load >50 copies/ml
- Suspected or confirmed active COVID infection within 30 days
- History of COVID vaccine within 28 days prior to enrollment, or other vaccine (influenza, shingles, etc.) within 14 days of enrollment, or planned use of any vaccine until the primary endpoint has been met (10 weeks)
- Other medical condition(s) or concomitant therapy that would compromise participant's safety or compliance with the study protocol or significantly confound interpretation of study results, as determined by study investigators
- Current enrollment in, or discontinuation within the last 30 days from, a clinical trial involving any investigational drug or device
- Inability to provide informed consent
- Currently hospitalized

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.
Please refer to this study by its ClinicalTrials.gov identifier (NCT number): NCT05576662
United States, California | |
Stanford University | |
Stanford, California, United States, 94305 |
Principal Investigator: | Upinder Singh, MD | Stanford University | |
Principal Investigator: | Linda Geng, MD, PhD | Stanford University |
Responsible Party: | Stanford University |
ClinicalTrials.gov Identifier: | NCT05576662 |
Other Study ID Numbers: |
66994 |
First Posted: | October 12, 2022 Key Record Dates |
Last Update Posted: | August 21, 2023 |
Last Verified: | August 2023 |
Individual Participant Data (IPD) Sharing Statement: | |
Plan to Share IPD: | No |
Plan Description: | Currently, there is no plan for data sharing. |
Studies a U.S. FDA-regulated Drug Product: | Yes |
Studies a U.S. FDA-regulated Device Product: | No |
COVID-19 Post-Acute COVID-19 Syndrome Pneumonia, Viral Pneumonia Respiratory Tract Infections Infections Virus Diseases Coronavirus Infections Coronaviridae Infections Nidovirales Infections RNA Virus Infections Lung Diseases Respiratory Tract Diseases Post-Infectious Disorders Chronic Disease |
Disease Attributes Pathologic Processes Ritonavir Nirmatrelvir HIV Protease Inhibitors Viral Protease Inhibitors Protease Inhibitors Enzyme Inhibitors Molecular Mechanisms of Pharmacological Action Anti-HIV Agents Anti-Retroviral Agents Antiviral Agents Anti-Infective Agents Cytochrome P-450 CYP3A Inhibitors Cytochrome P-450 Enzyme Inhibitors |