Phenobarbital and Tacrolimus interaction
Phenobarbital and Tacrolimus: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Phenobarbital (SEZABY) label · effective 2025-12-23
Drugs that Prolong the QT Interval : Avoid concomitant use.
QT Prolongation SEZABY may prolong the QT interval [see Clinical Pharmacology (12.2)] .
Drugs that Prolong QT Interval SEZABY may prolong the QT interval [see Warnings and Precautions (5.10) and Clinical Pharmacology (12.2)] .
Other products that may also prolong the QTc interval may have additive effects, and products that may increase concentrations of phenobarbital [see Drug Interactions (7.1)] may increase the QT prolongation risk; therefore, avoid concomitant use of SEZABY and these products.
From the Tacrolimus (ASTAGRAF XL) label · effective 2026-01-14
Risk of Rejection with Strong CYP3A Inducers and Risk of Serious Adverse Reactions with Strong CYP3A Inhibitors The concomitant use of strong CYP3A inducers may increase the metabolism of tacrolimus, leading to lower whole blood trough concentrations and greater risk of rejection.
…concentrations when co-administering ASTAGRAF XL with strong CYP3A inhibitors (e.g., including, but not limited to, telaprevir, boceprevir, ritonavir, ketoconazole, itraconazole, voriconazole, clarithromycin) or strong CYP3A inducers (e.g., including, but not limited to, rifampin, rifabutin) [see Dosage and Administration ( 2.4 ) and Drug Interactions ( 7.2 )] .
• Risk of rejection with strong CYP3A inducers and risk of serious adverse reactions with strong CYP3A inhibitors: Adjust dose and monitor tacrolimus concentrations.
Strong CYP3A Inducers c : Antimycobacterials (e.g., rifampin, rifabutin), anticonvulsants (e.g., phenytoin, carbamazepine and phenobarbital), St John’s wort May decrease tacrolimus whole blood trough concentrations and increase the risk of rejection [see Warnings and Precautions ( 5.10 )].
Mild or Moderate CYP3A Inducers Methylprednisolone, prednisone May decrease tacrolimus whole blood trough concentrations.
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.