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Pharmacology: Fexofenadine HCl is a third generation non-sedating H1-antihistamine. Fexofenadine is a pharmacologically active metabolite of terfenadine.
Human histamine wheal and flare studies following single and twice-daily doses of Fexofenadine HCl demonstrate that the drug exhibits an antihistaminic effect beginning within 1 hr, achieving maximum at 6 hrs and lasting 24 hrs. There was no evidence of tolerance to these effects after 28 days of dosing. A positive dose-response relationship between doses of 10-130 mg taken orally was found to exist. In this model of antihistaminic activity, it was found that doses of at least 130 mg were required to achieve a consistent effect that was maintained over a 24 hr period. Maximum inhibition in skin wheal and flares areas were >80%.
Fexofenadine at concentrations 32 times greater than the therapeutic concentration in man had no effect on the delayed rectifier K+ channel cloned from human heart. Fexofenadine HCl (5-10 mg/kg orally) inhibited antigen-induced bronchospasm in sensitised guinea pigs and inhibited histamine release at supratherapeutic concentrations (10-100 micromolar) from peritoneal mast cells.
Pharmacokinetics: Fexofenadine HCl is rapidly absorbed into the body following oral administration, with tmax occurring at approximately 1-3 hrs post-dose. The mean Cmax value was approximately 494 ng/ml following the administration of a 180 mg dose, once daily.
Fexofenadine is 60-70% plasma-protein bound. Fexofenadine undergoes negligible metabolism (hepatic or non-hepatic), as it was the only major compound identified in urine and feces of animals and man. The plasma concentration profiles of Fexofenadine follow a bi-exponential decline with a terminal elimination half-life ranging from 11-15 hrs after multiple dosing.
The major route of elimination is believed to be via biliary excretion while up to 10% of ingested dose is excreted unchanged through the urine.
