Introduction
Over the past few months, new drugs have been approved for the treatment of COVID-19 infection. Nirmatrelvir/ritonavir, approved in Spain in March 2022 for the treatment of mild COVID-19 infections in high-risk patients, has demonstrated an 89% reduction in the risk of progression to hospitalization and death when treatment is initiated within the first few days of symptom onset (1). The presence of ritonavir in this drug causes a rapid and strong inhibition of cytochrome P450 (CYP3A4), which represents the main pathway for the metabolism of a large number of drugs. This interaction can become especially relevant in transplant patients treated with tacrolimus, the main drug used in post-transplant immunosuppressive therapy, since it is metabolized in the liver and intestine by this enzyme (2). The interaction can cause elevations in tacrolimus blood levels leading to adverse effects such as nephrotoxicity or neurotoxicity.
In this study, we present the case of a kidney transplant patient who suffered a large elevation of tacrolimus blood levels due to interaction with nirmatrelvir/ritonavir.