Case Report: tacrolimus toxicity in the setting of concurrent Paxlovid use in a heart-transplant recipient.

Tacrolimus has a potent drug-drug interaction with Paxlovid (ritonavir-nirmatrelvir) and can be supra-therapeutic. Toxicity is associated with multiple adverse effects, including but not limited to, acute renal injury, neurotoxicity, and infections due to over-immunosuppression. As Paxlovid is effective in treating Sars-2-CoV-19 in heart-transplant recipients, knowledge and understanding of drug-drug interactions is crucial in preventing and mitigating toxicity.