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Pharmacology: Pharmacodynamics: Mechanism of action: Long-acting tricyclic antihistamine with selective peripheral histamine H1-receptor antagonistic properties and has been referred to as a relatively "nonsedating" or second generation antihistamine.
Pharmacokinetics: Onset of action: 1-3 hours.
Peak effect: 8-12 hours.
Duration: >24 hours.
Absorption: Rapid; food increase total bioavailability (AUC) by 40% to 48%.
Distribution: Vd 119 L/kg; binds preferentially to peripheral nervous system H1 receptors; no appreciable entry into CNS.
Protein binding: 97% to 99% (loratadine), 73% to 76% (metabolite).
Metabolism: Extensively hepatic via CYP2D6 and 3A4 to active metabolite (descarboethoxyloratadine).
Half-life elimination: 8.4 hours (range: 3 to 20 hours) (loratadine), 28 hours (range: 8.8 to 92 hours) (metabolite); hepatic impairment: 24 hours (loratadine), 37 hours (metabolite).
Time to peak, serum: Loratadine: 1.3 hours (loratadine), 2.3 hours (metabolite).
Excretion: Urine (40%) and feces (40%) as metabolites.
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