indication

A self-medication that is used alone or in combination with pseudoephedrine sulfate for the symptomatic relief of seasonal allergic rhinitis. Also used for the symptomatic relief of pruritus, erythema, and urticaria associated with chronic idiopathic urticaria in patients (not for children under 6 unless directed by a clincian).

pharmacology

Loratadine is a long acting second generation antihistamine that is similar in structure to cyproheptadine and azatadine. The pharmacology of loratadine is similar to other antihistamines, but unlike other H₁-blockers, loratidine is shown to exhibit competitive, specific, and selective antagonism of H₁ receptors. The exact mechanism of this interaction is unknown, but disposition of the drug suggests that loratadine's prolonged antagonism of histamine may be due to the drug's slow dissociation from the receptor or the formation of the active metabolite, desloratadine. Loratadine does not penetrate the CNS effectively and has a low affinity for CNS H₁-receptors.

mechanism of action

Loratadine competes with free histamine and exhibits specific, selective peripheral H₁ antagonistic activity. This blocks the action of endogenous histamine, which subsequently leads to temporary relief of the negative symptoms (eg. nasal congestion, watery eyes) brought on by histamine. Loratadine has low affinity for cholinergic receptors and does not exhibit any appreciable alpha-adrenergic blocking activity in-vitro. Loratadine also appears to suppress the release of histamine and leukotrienes from animal mast cells, and the release of leukotrienes from human lung fragments, although the clinical importance of this is unknown.

toxicity

somnolence, tachycardia, and headache LD₅₀=mg/kg (orally in rat)

biotransformation

Hepatic

absorption

Rapidly absorbed following oral administration (40% bioavailability)

half life

8.4 hours

drug interactions

Nefazodone: Increased risk of cardiotoxicity

Tacrine: The therapeutic effects of the central acetylcholinesterase inhibitor, Tacrine, and/or the anticholinergic, Loratadine, may be reduced due to antagonism. The interaction may be beneficial when the anticholinergic action is a side effect. Monitor for decreased efficacy of both agents.

Trimethobenzamide: Trimethobenzamide and Loratadine, two anticholinergics, may cause additive anticholinergic effects and enhance their adverse/toxic effects. Monitor for enhanced anticholinergic effects.

Triprolidine: Triprolidine and Loratadine, two anticholinergics, may cause additive anticholinergic effects and enhance their adverse/toxic effects. Additive CNS depressant effects may also occur. Monitor for enhanced anticholinergic and CNS depressant effects.

Trospium: Trospium and Loratadine, two anticholinergics, may cause additive anticholinergic effects and enhanced adverse/toxic effects. Monitor for enhanced anticholinergic effects.