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Loratadine is a widely used antihistamine primarily for allergy relief. Understanding its pharmacokinetics—absorption, distribution, metabolism, and excretion—is essential for effective use and safety.
Absorption of Loratadine
Loratadine is rapidly absorbed after oral administration. Its peak plasma concentration (Cmax) occurs approximately 1 to 2 hours post-dose. The drug has high oral bioavailability, estimated to be around 40%. Food intake may slightly delay absorption but does not significantly affect the overall extent of absorption.
Distribution of Loratadine
Loratadine is extensively distributed throughout body tissues. It has a high plasma protein binding rate, approximately 97%, mainly to albumin. This high binding affinity influences its distribution and limits its free active form in circulation.
Metabolism of Loratadine
The drug undergoes extensive hepatic metabolism primarily via the cytochrome P450 enzyme system, especially CYP3A4 and CYP2D6. Its main active metabolite, descarboethoxyloratadine, contributes significantly to its antihistaminic effects. Metabolism reduces the drug’s potential for sedative side effects compared to first-generation antihistamines.
Excretion of Loratadine
Loratadine and its metabolites are mainly excreted via the feces (about 66%) and urine (about 20%). The elimination half-life of loratadine is approximately 8 hours, but it can be prolonged in individuals with hepatic impairment. The drug’s clearance is primarily hepatic, with minimal renal elimination of the parent compound.