dilantin
5 interactions related to dilantin
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.
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.
phenytoin + vitamin d
Phenytoin induces hepatic CYP3A4 and CYP24A1, accelerating conversion of 25-hydroxyvitamin D to inactive metabolites and lowering circulating 25(OH)D, which over time produces secondary hyperparathyroidism, reduced calcium absorption, and a measurably increased risk of osteomalacia and fractures.
phenytoin + calcium
Phenytoin reduces calcium absorption by accelerating vitamin D catabolism and by directly inhibiting active transcellular calcium transport in intestinal enterocytes; separately, calcium-containing antacids and supplements can chelate phenytoin in the gut and lower its absorption when taken simultaneously.