Paxlovid with Caution: Novel Case of Paxlovid-Induced Tacrolimus Toxicity in a Cardiac Transplant Patient.

Tacrolimus is commonly used as a prophylactic against acute rejection in transplant patients. Tacrolimus toxicity has numerous presentations that have been well documented in the literature and can be induced by a wide variety of agents. We present a novel case of tacrolimus toxicity in a cardiac transplant patient induced by outpatient treatment for COVID-19 pneumonia with ritonavir-nirmatrelvir, which was successfully treated with phenytoin therapy. LEARNING POINTS: Ritonavir-nirmatrelvir is a newly approved antiviral therapy for COVID-19 to prevent hospitalization and is increasingly prescribed in the outpatient setting.Thorough assessment of drug interactions prior to starting ritonavir-nirmatrelvir can prevent tacrolimus toxicity in patients with solid organ transplants.Phenytoin increases the metabolism of tacrolimus and can be safely utilized to treat tacrolimus toxicity.