Blockage prevents the activation of the H1 receptors by histamine, preventing the symptoms associated with allergies from occurring. Fexofenadine does not readily cross the blood–brain barrier, so is less likely to cause drowsiness in comparison to other antihistamines that readily cross that barrier (i.e., first-generation antihistamines such as diphenhydramine). In general, fexofenadine takes about an hour to take effect, though this may be affected by the choice of dosage form and the presence of certain foods.Fexofenadine also exhibits no anticholinergic, antidopaminergic, alpha 1-adrenergic, or beta-adrenergic receptor-blocking effects. Pharmacokinetics
Absorption: After oral application, maximum plasma concentrations are reached after 2–3 hours. Fexofenadine should not be taken with a high-fat meal, as mean concentrations of fexofenadine in the bloodstream are seen to be reduced from 20 to 60% depending on form of medication (tablet, ODT, or suspension). Distribution: Fexofenadine is 60–70% bound to plasma proteins, mostly albumin. Metabolism: Fexofenadine is a substrate of CYP3A4, but only about 5% is metabolized by the liver, indicating that hepatic metabolism is relatively minor in clearance from the body. Elimination: Most of the substance is eliminated unchanged via the feces (80%) and urine (11–12%). Interactions
Taking erythromycin or ketoconazole while taking fexofenadine does increase the plasma levels of fexofenadine, but this increase does not influence the QT interval. The reason for this effect is likely due to transport-related effects, specifically involving p-glycoprotein (p-gp). Both erythromycin and ketoconazole are inhibitors of p-gp, a transporter protein involved in preventing the intestinal absorption of fexofenadine.
Pituitary adenomas are benign tumors that occur in the pituitary gland. Most pituitary tumors are benign, approximately 35% are invasive and just 0.1% to 0.2% are carcinomas. Pituitary adenomas represent from 10% to 25% of all intracranial neoplasms and the estimated prevalence rate in the general population is approximately 17%.Non-invasive and non-secreting pituitary adenomas are considered to be benign in the literal as well as the clinical sense; however a recent meta-analysis (Fernández-Balsells, et al. 2011) of available research has shown there are to date scant studies – of poor quality – to either support or refute this assumption. Adenomas exceeding 10 mm (0.39 in) in size are defined as macroadenomas, with those smaller than 10 mm (0.39 in) referred to as microadenomas. Most pituitary adenomas are microadenomas and have an estimated prevalence of 16.7% (14.4% in autopsy studies and 22.5% in radiologic studies). A majority of pituitary microadenomas often remain undiagnosed, and those that are diagnosed are often found as an incidental finding and are referred to as incidentalomas. Pituitary macroadenomas are the most common cause of hypopituitarism.While pituitary adenomas are common, affecting approximately one in 6 of the general population, clinically active pituitary adenomas that require surgical treatment are more rare, affecting approximately one in 1,000 of the general population. Signs and symptoms
Physical
Hormone secreting pituitary adenomas cause one of several forms of hyperpituitarism. The specifics depend on the type of hormone.