Horak et al54 conducted a randomized, placebo- controlled, investigator-blinded crossover study of fexofenadine 120 mg/d, cetirizine 10 mg/d, and pla- cebo in 39 subjects (51% male, 49% female; mean age, 26 years [range, 20–36 years]) with a ≥2-year his- tory of moderate to severe SAR. Subjects were ex- posed to allergen in the VCC for 6 hours on 2 con- secutive days. Both active drugs were associated with significant relief of total symptom complex (including nasal obstruction) at 2 to 6 hours after treatment on both study days (P < 0.05, both active drugs on both days). Nasal obstruction scores were improved signifi- cantly with both active drugs compared with placebo at 2 to 6 hours on day 1 and at 0 to 2 hours and 2 to 6 hours on day 2 (both, P < 0.05). Neither fexofena- dine nor cetirizine had any significant effects on nasal airflow, as measured by anterior rhinomanometry, compared with placebo. There were no significant dif- ferences between the active treatments.