DESCRIPTION
Loratadine is a derivative of azatadine and a second-generation histamine H1 receptor antagonist used in the treatment of allergic rhinitis and urticaria. Unlike most classical antihistamines (histamine H1 antagonists) it lacks central nervous system depressing effects such as drowsiness.
CATEGORIES
Anti-Allergic Agents,Antipruritics,Histamine H1 Antagonists, Non-Sedating,Histamine Antagonists.
CHEMICAL FORMULA
C22H23ClN2O2
COMPOSITION
Loratadine
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).
PHARMACODYNAMICS
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
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.
ABSORPTION
Rapidly absorbed following oral administration (40% bioavailability)
METABOLISM
Hepatic
ELIMINATION
40% as conjugated metabolites into urine
HALF LIFE
8.4 hours
TOXICITY
somnolence, tachycardia, and headache LD50=mg/kg (orally in rat) .
FOOD INTERACTIONS
avoid alchahol
SIDE EFFECTS
Feeling lightheaded, sleepy, having blurred eyesight, or a change in thinking clearly. Avoid driving and doing other tasks or actions that call for you to be alert or have clear eyesight until you see how this drug affects you. Headache. Dry mouth. Good mouth care, sucking hard, sugar-free candy, or chewing sugar-free gum may help. See a dentist often.