A clinically significant interaction between tacrolimus and multiple proton pump inhibitors in a kidney transplant recipient.

The shared metabolism of PPIs and tacrolimus through the CYP enzyme system has been associated with clinically significant drug interactions, especially in patients who are classified as CYP 2C19 PMs. However, existing data are conflicting, indicating that a single mechanism does not account for all interactions. A drug interaction between tacrolimus and omeprazole, esomeprazole, but not lansoprazole, occurred in an 18-yr-old female kidney transplant recipient classified as a CYP 2C19 extensive (normal) metabolizer. This case suggests that further research is needed to establish the definitive mechanism of this potentially serious drug-drug interaction. Physicians prescribing PPIs in organ transplant recipients with tacrolimus immunosuppression should consider close pharmacokinetic monitoring of tacrolimus when starting or switching a PPI.