Pfizer told by FDA to test additional Paxlovid course in patients with COVID-19 rebound

Pfizer has been told by the US Food and Drug Administration (FDA) to test the effects of an additional course of Paxlovid (nirmatrelvir and ritonavir tablets) among individuals who experience a rebound in COVID-19 after the first course of treatment.

The company must produce the initial results of a randomised controlled trial of a second course of the antiviral by 30 September next year, according to a letter from the regulator.

The order follows reports of rebounding COVID-19 symptoms after the first course of treatment, which Pfizer said were rare.

The FDA said a protocol for the study is expected to be finalised this month.

Paxlovid is an orally administered drug that should be given at the first sign of infection for the treatment of patients with mild-to-moderate COVID-19 in adults and paediatric patients – 12 years and older weighing at least 40kg – who are at high risk for progression to severe COVID-19.

Paxlovid has not been approved, but has been authorised for emergency use by FDA under an Emergency Use Authorisation (EUA) in December 2021, and has also been approved for emergency use in more than 65 countries.

Last month, Pfizer announced that the FDA has revised the EUA for Paxlovid, authorising pharmacists to prescribe the drug to eligible patients.

Under the revision, state-licensed pharmacists are able to prescribe the drug to patients testing positive for COVID-19, on the condition that they can provide recent health records and a list of current medicines they are taking.

In June, Pfizer announced the submission of a New Drug Application (NDA) to the FDA for the approval of Paxlovid for both vaccinated and unvaccinated patients who are at high risk of severe illness from COVID-19, consistent with current emergency use authorisation.

The NDA submission follows positive results from a phase 2/3 EPIC-HR study which demonstrated that, compared to placebo, treatment with Paxlovid reduced the risk of hospitalisation in non-hospitalised, high-risk adult patients treated within five days of symptom onset or death from any cause by 88%.