carbamazepine
4 interactions related to carbamazepine
carbamazepine + biotin
Carbamazepine gradually lowers biotin (vitamin B7) status by reducing intestinal absorption, increasing urinary loss, and accelerating breakdown of the vitamin. The effect is biomarker-level and well documented over decades; frank deficiency and serious adult harm are uncommon.
grapefruit + carbamazepine
Grapefruit juice inhibits the intestinal CYP3A4 enzyme that performs first-pass metabolism of carbamazepine, allowing more of each oral dose to reach the bloodstream. A human study in epilepsy patients found grapefruit juice raised carbamazepine blood levels, which matters because carbamazepine has a narrow safety margin.
carbamazepine + vitamin d
Carbamazepine activates the pregnane X receptor and induces the liver enzymes (including CYP3A4 and CYP24A1) that break down vitamin D, accelerating the clearance of 25-hydroxyvitamin D into inactive metabolites. A meta-analysis and observational studies consistently show lower 25(OH)D in long-term carbamazepine users, along with a secondary-hyperparathyroidism pattern and reduced bone density that raises fracture risk over years of therapy.
carbamazepine + st. john's wort
Both carbamazepine and St. John's Wort induce CYP3A4, the liver enzyme that primarily breaks carbamazepine down. The combined effect is hard to predict: carbamazepine already induces its own metabolism, so adding the herb may lower exposure most before that self-induction is fully established. The bigger danger comes at transitions — especially stopping St. John's Wort while still on carbamazepine, when the loss of enzyme induction can let carbamazepine levels climb toward toxicity.