Delayed Drug-Drug Interaction Between Antiviral Drugs and Tacrolimus in a Pancreatic Islet Transplant Recipient With SARS-CoV-2 Pneumonia.

Background: PAXLOVID (nirmatrelvir and ritonavir) and VEKLURY (remdesivir) are the first- and second-line antivirals administered to adult patients at risk of severe forms of SARS-CoV-2 infection (COVID-19), such as transplant recipients. As this specific population requires lifelong immunosuppressive treatments, the administration of antivirals with cytochrome P450-modulating properties exposes patients to a high risk of drug-drug interactions (DDI).

Case presentation: A 72-year-old male patient who underwent a pancreatic islet transplant experienced DDI between antiviral treatment and tacrolimus during the management of SARS-CoV-2 pneumonia. The patient received a single dose of nirmatelvir/ritonavir followed by a single dose of remdesivir. Tacrolimus treatment was interrupted for the duration of the antiviral treatment, and the concentration of tacrolimus was within the target range for this patient. Once antiviral treatment was stopped, tacrolimus was reintroduced at the initial dose. On day 6, the patient presented with clinical and biological parameters consistent with a tacrolimus overdose. A trough concentration 18 times higher than the therapeutic target was found, prompting tacrolimus to be discontinued for 9 days and reintroduced at a lower dose, followed by a gradual increase based on therapeutic drug monitoring to the initial dose. Clinical and biological parameters gradually returned to baseline levels.

Conclusions: Management of DDI between tacrolimus and anti-SARS-CoV-2 drugs requires a substantial therapeutic intervention and close therapeutic drug monitoring during and for several days after antiviral treatment.