title: Phenytoin-associated severe hypocalcemia with seizures in a patient with a TSC2-PKD1 contiguous gene syndrome.
abstract: We report the case of an inaugural episode of generalized seizures in a 40-year-old male with a history of chronic kidney disease associated with TSC2-PKD1 contiguous gene syndrome. This patient was under prophylactic treatment of phenytoin since 2 years because of a subarachnoid hemorrhage due to a ruptured cerebral aneurysm. Laboratory results revealed therapeutic range of phenytoin levels, but severe hypocalcemia associated with profound vitamin D deficiency that could not be explained by secondary hyperparathyroidism alone. The interaction of phenytoin on the P-450 cytochromes activity has been demonstrated to accelerate the rate of 25-hydroxivitamin D3 and 1α,25-dihydroxivitamin D3 catabolism into inactive metabolites, leading to hypocalcemia. Physicians should be aware of significant phenytoin interactions on vitamin D metabolism which may lead to symptomatic hypocalcemia in patients with chronic kidney disease.
authors.affiliation: Transplantation Center, Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland.
authors.forename: Ghaleb
authors.initials: G
authors.lastname: Nseir
authors.forename: Dela
authors.initials: D
authors.lastname: Golshayan
authors.forename: Frédéric
authors.initials: F
authors.lastname: Barbey
mesh_terms: D000328:Adult; D000927:Anticonvulsants / Q000009:adverse effects*; D006801:Humans; D006996:Hypocalcemia / Q000139:chemically induced*; D008297:Male; D010672:Phenytoin / Q000009:adverse effects*; D051436:Renal Insufficiency, Chronic / Q000150:complications* / Q000235:genetics; D013577:Syndrome; D050396:TRPP Cation Channels / Q000235:genetics*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics*; D014808:Vitamin D Deficiency / Q000139:chemically induced*
chemical_list: D000927:Anticonvulsants; D010672:Phenytoin; D050396:TRPP Cation Channels; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C000624653:TSC2 protein, human