Possible Interaction: Phenytoin and Vitamin D

“Physicians should be aware of significant phenytoin interactions on vitamin D metabolism which may lead to symptomatic hypocalcemia in patients with chronic kidney disease.”

“If osteoporosis is diagnosed, vitamin D therapy may be necessary in conjunction with phenytoin , particularly for women [15].”

“The interference of sodium diphenylhydantoins on Vitamin D metabolism causing or aggravating ricketts has also been reported.”

“After being cured of this, and while on a maintenance dose of vitamin D , the addition of diphenylhydantoin sodium was accompanied by a recurrence of the rickets, which was corrected by raising the dosage of vitamin D from 600 to 1,200 international units per day.”

“Furthermore, cholecalciferol (at its highest subthreshold dose of 18.75 mug) potentiated the anticonvulsant activity of phenytoin and valproate.”

“This work supports the theory that chronic DPH treatment can antagonize the antirachitic effect of calciferol and so produce “anticonvulsant osteomalacia” in humans and animals.”

“ Phenytoin has also been shown to be an effective inhibitor of bone resorptionin vitro induced by 25-hydroxycholecalciferol.”

“Combined administration of either alfacalcidol or calcitriol with phenytoin for 5 weeks prevented the reduction of BMD induced by phenytoin.”

“Moreover, combined administration of alfacalcidol or calcitriol with phenytoin showed a preventative effect against bone loss.”

“These same enzymes increase the metabolism of vitamin D and 25‐hydroxyvitamin D when induced by chronic barbiturate or phenytoin administration.”

“The fluorescence studies performed in mitochondrial subfractions revealed that cholecalciferol treatment induces a decrease of lipid order parameter S ( DPH ) in the mitochondrial inner membrane.”