Cetirizine is the carboxylated metabolite of hydroxyzine, and has high specific affinity for histamine H(1) receptors. Pseudoephedrine is a sympathomimetic drug that acts directly on alpha-adrenergic receptors. black triangle Cetirizine/pseudoephedrine 5/120 mg twice daily was significantly more effective than intranasal budesonide 100 microg or placebo at improving nasal obstruction, nasal patency and reducing the volume of nasal secretion, and was significantly more effective than intranasal xylometazoline 0.1% with respect to nasal secretion, during house dust mite faeces challenge in three randomised, cross- over studies among volunteers with seasonal or perennial rhinitis. The onset of action of cetirizine/pseudoephedrine was reported to be approximately 30 minutes. black triangle The bioavailability of cetirizine and pseudoephedrine is similar after administration of cetirizine/pseudoephedrine 5/120 mg bilayer tablets or coadministration of cetirizine 5 mg tablets plus pseudoephedrine sustained-release (SR) 120 mg caplets. black triangle Cetirizine 5mg plus pseudoephedrine SR 120 mg twice daily for 2 to 3 weeks was significantly more effective than each drug given alone at reducing mean total symptom scores for seasonal or perennial allergic rhinitis in two randomised, double-blind, multicentre trials. In both studies, the mean proportion of days during which the five measured symptoms (nasal obstruction, sneezing, rhinorrhoea, nasal pruritus and ocular pruritus) were absent or mild was significantly greater in recipients of the cetirizine plus pseudoephedrine SR. black triangle In one study, cetirizine 5 mg plus pseudoephedrine SR 120 mg was significantly more effective at reducing nasal obstruction than either drug alone. black triangle Cetirizine 5mg plus pseudoephedrine SR 120 mg twice daily for 2 to 3 weeks was well tolerated in patients with seasonal or perennial allergic rhinitis. The most common adverse events were dry mouth, insomnia, headache, somnolence, asthenia and nervousness.