Assessment of Different Cetirizine Dosing Strategies on Seasonal Allergic Rhinitis Symptoms: Findings of Two Randomized Trials.

Background: Cetirizine has been shown to be effective for relief of seasonal allergic rhinitis (SAR) symptoms. Allergic rhinitis symptoms have been reported to have circadian variations, with symptoms tending to be most bothersome overnight and in the morning.

Objective: To evaluate the effects of different cetirizine dosing schedules in comparison to twice daily (BID) chlorpheniramine and placebo on SAR symptoms at 12 and 24 hours postdose.

Methods: Study 1 subjects received cetirizine 10-mg once daily in the morning (QAM), cetirizine 10-mg once daily at bedtime (QHS), cetirizine 5-mg twice daily, or placebo. Study 2 subjects received cetirizine 5-mg QAM, cetirizine 10-mg QHS, chlorpheniramine 8-mg BID, or placebo. The primary end point was total symptom severity complex (TSSC); TSSC was the sum of symptom severity ratings averaged over the 2-week study period. Post hoc analyses of reflective symptom severity assessed in the morning (TSSCAM ) and in the evening (TSSCPM ) were conducted to evaluate cetirizine's effects at 12 and 24 hours postdose.

Results: In study 1, subject- and investigator-assessed TSSC was significantly lower in all cetirizine groups versus placebo ( P ≤ .003). In study 2, subject-assessed TSSC was significantly lower in all cetirizine groups versus placebo ( P ≤ .04) and was numerically lower for investigator-assessed TSSC. Post hoc analyses demonstrated that cetirizine significantly improved TSSCAM at 12 and 24 hours postdose versus placebo in both studies regardless of dosing schedule. TSSCPM significantly improved at 12 and 24 hours postdose in all study 1 cetirizine groups versus placebo. In study 2, versus placebo, TSSCPM significantly improved at 12 hours postdose in cetirizine 5-mg QAM group and numerically improved at 24 hours postdose in cetirizine 10-mg QHS group.

Conclusion: Regardless of dosing regimen, cetirizine demonstrates effective 24-hour relief of SAR symptoms, particularly on TSSCAM , which assesses overnight and early morning symptom control.