Paxlovid (Nirmatelvir/Ritonavir) and Tacrolimus Drug-Drug Interaction in a Kidney Transplant Patient with SARS-2-CoV infection: A Case Report

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has had a significant impact on communities and health systems. New antiviral medications against this disease have not been properly tested yet, and their efficiency, side effects, and drug–drug interactions are not entirely known. Organ transplant recipients receive immunosuppressive medications such as tacrolimus to prevent graft rejection. Tacrolimus is metabolized by the cytochrome P450 3A4 enzyme system. Many medications can either induce or inhibit this enzyme and affect the level. Awareness of possible drug–drug interactions is vital because tacrolimus levels should be kept within a specific narrow range determined by the recipient's immunologic risk. Underexposure increases the risk of graft rejection, whereas overexposure may lead to adverse effects. Paxlovid, a novel antiviral medication approved for emergency use to treat SARS-CoV-2, is a combination of nirmatrelvir and ritonavir, a cytochrome P450 34A inhibitor. In this case report, we present a case of a kidney transplant patient receiving tacrolimus treated with Paxlovid, leading to an abruptly high tacrolimus level, significant symptoms, treatment interruption, and acute kidney injury. We conclude that the drug–drug interaction between Paxlovid and tacrolimus is indeed robust and noteworthy and leads to high tacrolimus levels and its metabolites, adverse effects, and acute kidney injury. Physicians managing immunocompromised patients receiving tacrolimus should be aware of this significant drug–drug interaction and consider other options or reduction of daily tacrolimus dose during treatment in addition to timely monitoring of both tacrolimus levels and serum creatinine. Consulting with the transplant pharmacist is foremost in alerting for these interactions.