In this analysis, 1,039 participants had received nirmatrelvir/ritonavir, and 1,046 participants had received placebo and among these participants, 0.8% who received nirmatrelvir/ritonavir were hospitalized or died during 28 days of follow-up compared to 6% of the participants who received placebo.In September 2021, Pfizer began a phase II/III trial of nirmatrelvir combined with ritonavir.In December 2021, Pfizer completed a Phase III study of nirmatrelvir combined with ritonavir, and on 14 December, Pfizer announced that the Phase II/III study of nirmatrelvir combined with ritonavir showed a reduced risk of hospitalization or death. In December 2021, nirmatrelvir/ritonavir was granted emergency use authorization by the United States Food and Drug Administration (FDA) for the treatment of COVID-19. On 31 December, the United Kingdoms Medicines and Healthcare products Regulatory Agency (MHRA) approved the use of nirmatrelvir combined with ritonavir for adults with mild to moderate infection and at high risk of their illness worsening.The efficacy of the co-packaged medication against hospitalization or death in high-risk adults when administered within five days of symptom onset is about 88% (95% CI, 75–94%).In 2022, the PANORAMIC trial started testing the effectiveness of nirmatrelvir/ritonavir for treating COVID-19 infections.Pfizer also conducted a Phase II/III study in standard-risk patients called EPIC-SR, which began in December 2021. This study did not find a statistically significant reduction in the risk of hospitalization or death (treatment: 5/576; placebo: 10/569), nor did it achieve its primary goal of sustained alleviation of symptoms.
Chemical & Engineering News. Vol. 100, no. 3. Regalado A (February 2022). "How Pfizer made an effective anti-covid pill". MIT Technology Review. COVID 19 Drug interaction check tool University of Liverpool