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9th November 2021
Paxlovid given within three days of symptom onset to patients with COVID-19 significantly reduced the risk of hospitalisation and death. These were the results of an interim analysis posted by the manufacturer, Pfizer.
Paxlovid is a combination of Pfizer’s experimental drug (PF-00835231) and ritonavir. Both are protease inhibitors, a class of anti-viral drugs that have been used in the treatment of viral infections such as HIV and hepatitis C. COVID-19 produces a protease termed Mpro, which is vital to viral replication, and PF-00835231 been been found to be a potent inhibitor of Mpro. According to the manufacturer, co-administration of PF-00835231 and a low dose of ritonavir helps slow the metabolism of PF-07321332 so that it remains active for a longer period of time and at higher concentrations to help combat the virus.
In a clinical study, Paxlovid was used for the treatment of adults infected with COVID-19 but who, at the time of their illness, were not deemed sufficiently unwell to require hospitalisation but who were, however, considered to be at a higher risk of developing more severe illness. The study, Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients (EPIC-HR), is a randomised, 1:1, double-blind study, in which individuals received paxlovid or placebo orally every 12 hours for 5 days. The primary outcome of the study was the proportion of participants with COVID-19 related hospitalisation or death from any cause between days 1 and 28 after randomisation.
According to a pre-specified interim analysis based on 1219 participants, there was an 89% reduction in risk of COVID-19-related hospitalisation or death from any cause compared to placebo, in patients treated within three days of symptom onset. Overall, 3/389 (0.8%) who received paxlovid were hospitalised through to day 28 and there were no deaths but among 385 participants assigned to placebo, 27/395 (7.0%) were hospitalised and there were 7 deaths and this difference compared with Paxlovid was statistically significant (p < 0.0001).
Among patients treated within 5 days of symptom onset, 1.0% of those given Paxlovid were hospitalised through to day 28 (6/607) compared with 6.7% (41/612) of those given placebo (p < 0.0001). Moreover, to date, there have been no deaths were reported in patients receiving Paxlovid and 10 deaths in the placebo group.
Based on a recommendation of the independent data monitoring committee and after consultation with the FDA, Pfizer will cease further enrolment and submit the data for the FDA’s emergency use authorisation (EUA) as soon as possible.
Further trials with Paxlovid are on-going and the company will release these results in due course.