Carbamazepine rarely causes stimulation of the release of the antidiuretic hormone by the posterior pituitary. Clinically, this most often manifests as peripheral edema and may account for some of the excess weight gain. Most patients are asymptomatic. However, if a patient becomes symptomatic, carbamazepine discontinuation is recommended. Whether hyponatremia occurs more frequently with oxcarbazepine, which is structurally related to carbamazepine, is not known.
Although phenytoin and other anticonvulsants lower total free T4 levels and the free thyroxine index, there is no clinical evidence that they cause hypothyroidism ; this is thought to be due to the enhanced peripheral conversion of T4 to T3. However, in patients with primary hypothyroidism, initiation of phenytoin may increase thyroxine replacement requirements.
Results from studies that have investigated the effects of long term antiepileptic therapy on the hypothalamic-pituitary axis have been conflicting. One study did not find any significant changes in hypothalamic-pituitary axis function in children induced by long term monotherapy with either carbamazepine or valproate. Phenytoin can affect sex hormones by stimulating microsomal metabolism of estradiol, estrone and progesterone. Most reliable pharmacy can offer Zyrtec tablets always charging you a lot less.