Elevated tacrolimus levels after treatment with nirmatrelvir/ritonavir (Paxlovid) for COVID-19 infection in a child with a kidney transplant

BACKGROUND: Paxlovid (nirmatrelvir/ritonavir) is a novel drug available under emergency use authorization by the Food and Drug Administration for the treatment of COVID-19 infection. Tacrolimus, a calcineurin inhibitor, is commonly used as an immunosuppressant medication in children with kidney transplants. While tacrolimus is metabolized by the cytochrome P450 system (CYP3A4), ritonavir is a potent CYP3A4 inhibitor. There is a paucity of data regarding the drug-drug interaction between nirmatrelvir/ritonavir and tacrolimus in children with kidney transplants. CASE-DIAGNOSIS/TREATMENT: This is a case report of a 14-year-old female with a history of a kidney transplant, maintained on tacrolimus and prednisone, who starts nirmatrelvir/ritonavir for a COVID-19 infection. She subsequently develops supratherapeutic tacrolimus levels and an increase in serum creatinine. Her tacrolimus was held, and the nirmatrelvir/ritonavir was stopped. Over time, her kidney function returned to baseline, her tacrolimus levels returned to the therapeutic goal, and her tacrolimus was resumed. CONCLUSIONS: Our case report highlights the strong interaction with concomitant use of tacrolimus and nirmatrelvir/ritonavir in a pediatric kidney transplant recipient and the development of supratherapeutic tacrolimus levels. Providers should therefore be cautious when prescribing nirmatrelvir/ritonavir to a pediatric patient currently on tacrolimus.