Medicinal Mishap: Acute tacrolimus toxicity due to concomitant use of ritonavir (with nirmatrelvir as Paxlovid)

Co-administration with ritonavir can cause a rapid increase in the concentration of tacrolimus, leading to acute tacrolimus toxicity. This case highlights the importance of being vigilant for potential drug interactions when introducing a new medication, particularly if the patient is using a drug with a narrow therapeutic index, such as tacrolimus.