ABSTRACT
Paxlovid (nirmatrelvir plus ritonavir) is a new oral antiviral therapeutic for the treatment and post-exposure prophylaxis of COVID-19. Nirmatrelvir is an inhibitor of SARS-CoV-2 main protease, while ritonavir is used as a CYP3A inhibitor in low doses to slow the metabolism of nirmatrelvir, thus enhancing their therapeutic effect. The isoenzyme CYP3A4 is responsible for at least part of the oxidative metabolism of approximately 60% of available medications and ritonavir is therefore a significant source of drug interactions. We describe here the drugs that are contraindicated or should be used with or without precautions when Paxlovid (nirmaltrevir plus ritonavir) should be administered according to each fact sheet in force at the Spanish Agency for Medicines and Health Products.