enzyme induction
8 interactions related to enzyme induction
verapamil + st. john's wort
St. John's wort is a potent inducer of intestinal CYP3A4 and P-glycoprotein. In a controlled study, two weeks of St. John's wort reduced the AUC of R- and S-verapamil by roughly 78-80%, dramatically lowering systemic drug exposure and likely therapeutic effect.
digoxin + st. john's wort
St. John's wort induces intestinal P-glycoprotein, increasing efflux of digoxin and reducing its absorption. Controlled studies show digoxin AUC falls roughly 25% and peak concentrations around 30-36% after two weeks of St. John's wort, potentially producing therapeutic failure in rate control or heart failure management.
phenytoin + st. john's wort
St. John's Wort is a potent inducer of CYP3A4, CYP2C9, CYP2C19, and P-glycoprotein via activation of the pregnane X receptor. Because phenytoin is heavily metabolized by CYP2C9 and CYP2C19, concurrent St. John's Wort can lower phenytoin plasma concentrations into the subtherapeutic range, increasing the risk of breakthrough seizures.
phenytoin + ginkgo
Ginkgo biloba induces CYP2C19, the primary enzyme responsible for phenytoin metabolism. A published case report described a fatal breakthrough seizure in a patient on phenytoin and valproate whose autopsy revealed subtherapeutic anticonvulsant levels and self-administration of ginkgo biloba. Ginkgo also has independent pro-convulsant potential at high doses and through ginkgotoxin contamination.
oxycodone + st. john's wort
St. John's Wort strongly induces CYP3A4, the main enzyme that metabolizes oxycodone. In a controlled crossover trial, St. John's Wort cut oral oxycodone plasma exposure (AUC) by roughly 50% and significantly reduced its analgesic effect.
phenytoin + folate
Phenytoin lowers serum and red-cell folate through enzyme induction and impaired absorption of polyglutamate folates, but high-dose folate supplementation in turn accelerates phenytoin metabolism and can drop drug levels enough to cause seizure breakthrough.
omeprazole + st. john's wort
St. John's wort potently induces CYP3A4 and CYP2C19, the enzymes responsible for omeprazole metabolism. Co-administration significantly lowers omeprazole plasma concentrations, reducing its acid-suppressing efficacy and potentially compromising treatment of GERD, ulcers, or H. pylori eradication.
carbamazepine + st. john's wort
Both carbamazepine and St. John's Wort are strong inducers of CYP3A4, the enzyme that primarily metabolizes carbamazepine. Although healthy-volunteer studies have shown limited additional effect on chronic carbamazepine kinetics (because carbamazepine already maximally autoinduces its own metabolism), starting or stopping St. John's Wort can destabilize carbamazepine levels, and the herb can lower exposure to single carbamazepine doses by up to 21% before autoinduction is established.