Biotech & drug discovery · Oral antivirals
Pardes Biosciences
A COVID-19 pill drawn up in the first weeks of the pandemic, taken public through a blank check company, and stopped after a single Phase 2 trial. In August 2023 it was bought out by the venture firm that had sponsored the vehicle that listed it.
A common cold with a bad attitude
In February 2020 Uri Lopatin was a visiting partner at Y Combinator. He called Lee Arnold, a chemist he had worked with at Assembly Biosciences, and they looked at the new coronavirus the way medicinal chemists do: as a protein with a soft spot.
“When the pandemic hit, I was having a conversation with Lee Arnold, our CSO,” Lopatin later told GEN. “We noticed that SARS-CoV-2 looked a lot like SARS and MERS.” His summary of the threat was blunter: “SARS-CoV-2 is like a common cold with a bad attitude.”
They incorporated on February 29, 2020, filed patents, and ran the chemistry through contract research organizations without renting a lab. The target was the coronavirus main protease, the enzyme that cuts one long viral polyprotein into the 16 pieces the virus needs to copy itself.
“You can think of it like pearls on a string,” Lopatin said of the polyprotein. The protease is the scissors. “And that particular pair of scissors is what we break.”
The gap they aimed at
By late 2021 two COVID-19 pills had emergency authorization. Pfizer’s Paxlovid was a protease inhibitor like the Pardes compound, and it worked, but it had to be given with ritonavir, a metabolic booster that collides with a long list of common medicines.
That list was the commercial thesis. Pardes said its compound was designed to work alone, without a booster, and so without the interaction problem that keeps Paxlovid away from patients on blood thinners or antipsychotics. Heidi Henson, the chief financial officer, put the goal plainly in the Los Angeles Times: “The world needs some sort of pill that you can take at home.”
A short road to the public market
The company raised roughly $52 million in January 2021, then in June agreed to merge with FS Development Corp. II, a blank check company sponsored by Foresite Capital. Gilead Sciences joined a $75 million concurrent placement alongside RA Capital, Frazier Life Sciences, EcoR1 and accounts advised by T. Rowe Price. Foresite’s chief executive, James Tananbaum, already sat on the Pardes board.
The merger closed on December 23, 2021, four months after the first human dose, with net proceeds of about $257.5 million from the combination and the placement. A year later Pardes held $197.3 million, employed 57 people, and carried an accumulated deficit of $148.2 million.
Lopatin handed the chief executive job to Thomas G. Wiggans in March 2022 and became chief scientific and strategic advisor. Wiggans had run Dermira and Peplin, both sold.
Two hundred and forty two patients
Study PBI-0451-0002 opened on September 21, 2022: double blind, randomized, quadruple masked, in non hospitalized adults aged 18 to under 65 with mild to moderate COVID-19, vaccinated, symptomatic for five days or less, and with no risk factors for severe disease. Participants were randomized two to one to pomotrelvir 700 mg twice daily for five days, or to matching placebo.
The primary endpoint was narrow and virological: the proportion below the limit of detection for infectious SARS-CoV-2 on day 3, by infectious virus assay on nasal swabs.
On March 14, 2023 Wiggans told investors the company was “excited and remain on track to share the results from this study in the coming weeks and feel well positioned to rapidly advance this program into its next stage of development and to patients in need.”
Three weeks later the number arrived. Seventy percent of treated participants were below the limit of detection on day 3, against 63 percent on placebo, p=0.57. Nothing separated the arms on viral load by PCR either, and median time to alleviation of the five key symptoms was six days in both groups. The drug was well tolerated. It did nothing the placebo did not do.
The registry gives the reason for stopping in one line: “Interim analysis concluded primary endpoint was not met.” The peer reviewed write up in Microbiology Spectrum offered an explanation rather than a defence, noting that virus cleared so fast in vaccinated people that late dosing left little to block, “which suggests that delayed initiation of treatment (up to 5 days after symptom onset) may have contributed to the lack of treatment response.”
The same day the board approved cutting headcount by about 85 percent and opened a review of strategic alternatives. The company held $172.4 million.
The buyer was already in the room
What followed was a cash shell auction. A special committee of four independent directors, advised by Leerink Partners and Fenwick & West, started from 133 possible reverse merger candidates, solicited nine, received eight proposals, and shortlisted three. It also approached financial buyers. Tananbaum was excluded from board discussion of the process from April 13, 2023.
Foresite won. On July 17, 2023 Pardes agreed to be acquired by MediPacific, a Foresite entity, for at least $2.02 a share plus up to $0.17 more depending on net cash, and one non transferable contingent value right per share carrying 80 percent of the net proceeds from any sale or licence of the antiviral portfolio within five years. Fierce Biotech read it plainly: “the biotech has been bailed out via an acquisition by its key shareholders.”
The tender closed on August 30, 2023 at $2.13 a share. Trading in PRDS stopped the next morning.
What is proven, and what is still claimed
| Evidence | What the record shows | Source type |
|---|---|---|
| Phase 1 | NCT05011812, single and multiple ascending dose in healthy subjects. 130 enrolled, randomized, triple masked. Aug 14, 2021 to Mar 26, 2022. Completed. | Public record |
| Phase 2 design | NCT05543707. Randomized, quadruple masked, 242 participants, 2:1 to 700 mg twice daily for 5 days. Primary endpoint: proportion below the limit of detection for infectious SARS-CoV-2 on Day 3 by infectious virus assay. Terminated. | Public record |
| Phase 2 result | Endpoint missed: 70% versus 63% on placebo, p=0.57. No separation on viral load by qRT-PCR. Median time to alleviation of five key symptoms 6 days in both arms. | Public record |
| Reason for stopping | Registry field: “Interim analysis concluded primary endpoint was not met.” Primary completion Jan 27, 2023; study completion Apr 14, 2023. | Public record |
| Site count | The April 2023 release says 63 US sites. The registry lists 54 locations. | Differs from registry |
| Framing before the readout | Three weeks before the result the company said it was “greatly encouraged by the progress made in our ongoing Phase 2 study.” | Company-stated |
| Publication | Phase 2 viral dynamics in Microbiology Spectrum, PMID 38197702, February 2024. The disclosure note states all authors are former employees. | Public record |
| Federal grants | No NIH or NSF awards to the company found as of Sep 22, 2026. The program ran on private capital. | Not found |
| Contingent value rights | The offer document states: “Pardes’ estimate as to the amount that may be payable under the CVRs is $0.00.” No disposition reported as of Sep 22, 2026. | Public record |
Read plainly: the safety profile was clean and it did not matter. The trial asked whether the drug cleared infectious virus faster than placebo in vaccinated adults who were already clearing it quickly, and the answer was no. What the company did well was hand the money back in an orderly way. The science went to the buyer, with holders keeping a claim on 80 percent of whatever it fetches and the company itself valuing that claim at zero.
What to watch
- Any disposition of the pomotrelvir portfolio before the five year window closes on August 31, 2028. That is the only event that pays a CVR holder anything.
- Whether the delayed dosing explanation is tested by others. The published analysis argues future COVID-19 antiviral studies may need to start treatment earlier.
- The pardesbio.com domain has lapsed and now serves unrelated commercial content, so company statements survive only in SEC filings and press archives.
In their words
“SARS-CoV-2 is like a common cold with a bad attitude.”
Uri Lopatin, co-founder and then CEO, GEN Edge, 2021 · Interview
“The world needs some sort of pill that you can take at home.”
Heidi Henson, CFO, Los Angeles Times, 2021 · Independent
“these unexpected results have forced us to make the difficult decision to suspend further development of pomotrelvir and pursue alternative strategic opportunities for the company”
Thomas G. Wiggans, CEO and chair, results release, April 2023 · Company release
“the data indicated it was likely the vaccine rather than Pomotrelvir doing most of the work”
Nicholas Alan Clayton, SPACInsider, 2023 · Independent
“the biotech has been bailed out via an acquisition by its key shareholders”
James Waldron, Fierce Biotech, 2023 · Independent
“Pardes’ estimate as to the amount that may be payable under the CVRs is $0.00.”
Offer to Purchase, SEC, August 2023 · Public record
Related companies
Sources
- Public recordClinicalTrials.gov NCT05543707 and NCT05011812
- Public recordForm 10-K for the year ended December 31, 2022
- Public recordForm 8-K, workforce reduction and preliminary cash
- Public recordSchedule 14D-9, background of the offer
- Public recordAmended and Restated Offer to Purchase
- Public recordForm 10-Q for the quarter ended June 30, 2023
- Public recordForm 8-K and exhibit 99.1, closing of tender offer
- Public recordForm D, CIK 0001842257
- Public recordSARS-CoV-2 viral dynamics in a phase 2 study
- IndependentPardes to suspend COVID-19 drug development after trial fails
- IndependentPardes Biosciences changes hands (sort of)
- IndependentPardes Biosciences (PRDS) to Be Acquired by MediPacific
- IndependentPardes Bio’s Covid-19 pill still fills in Foresite’s blank check
- IndependentPardes Biosciences nets $199 million to keep pace in COVID-19 pill race
- InterviewPardes Biosciences Advances Oral Antiviral Drug
- CompanyTop-line Phase 2 results for pomotrelvir
- CompanyFourth Quarter and Full Year 2022 Financial Results
Profile researched and written by Healthcare Discovery. Last updated September 29, 2026.
