Sunizine Mechanism of Action

Pharmacology: In experimental animals, cetirizine has been shown to be an anti-H1 agent devoid of any significant anticholinergic or antiserotonin effects. At pharmacological active doses, it induces neither sedation nor behavioural changes. This may be explained by the fact that cetirizine does not cross the blood-brain barrier.
It was shown in human pharmacology studies that cetirizine will inhibit certain effects produced by exogenous histamine. This activity appears rapidly. Cetirizine also inhibits the effects produced by endogenous histamine released in vivo by an agent eg 48/80. Finally, it inhibits the cutaneous reaction induced by VIP (Vasoactive Intestinal Polypeptide) and substance P, neuropeptides that are believed to take part in the allergic reaction.
Cetirizine markedly reduces bronchial hyper-reactivity to histamine in the asthmatic patient. It also reduces the allergic reaction induced by specific allergens. These effects are obtained without central effects being demonstrated either by psychometric test or by a quantified EEG.
Pharmacokinetics: Peak blood levels of the order of 0.3 mg/ml are reached between 30 and 60 minutes after administration of a 10 mg dose of cetirizine. Its plasma half-life is approximately 11 hours. Absorption is very consistent from one subject to the next. Its renal clearance is 30 ml/minute and the excretion half-life is approximately 9 hours. Cetirizine is strongly bound to plasma proteins.