CKS could find no systematic reviews evaluating the effects of intranasal antihistamines, or, comparing the benefits of different oral antihistamines. However, there is evidence from placebo-controlled randomized controlled trials (RCTs) that antihistamines improve quality of life and rhinitis symptoms [Sheikh et al, 2007a]. A similar benefit was found in most trials which compared intranasal with oral antihistamines.

• A systematic review investigated the effect of oral antihistamines on the symptom of nasal obstruction in people with persistent allergic rhinitis [Hore et al, 2005]. This review was conducted as oral antihistamines have been considered to have a limited effect on nasal obstruction [van Cauwenburge et al, 2000]. Cochrane, Medline, and Embase were searched up to June 2002, and relevant hand searches were also performed.
• Of 89 potentially eligible studies identified, only seven met inclusion criteria and of these four (antihistamine group, n = 4, and placebo group, n = 126) contained data that could be pooled.
• Meta-analysis found a weighted mean difference of:
• –0.52 in favour of treatment for patient-assessed symptom scores (95% CI –0.73 to –0.31, p < 0.001). This represented a 32% change in symptoms on top of any placebo effect.
• –0.33 in favour of treatment for healthcare worker assessed scores (95% CI –0.49 to –0.16, p = 0.0001). This represented a 22% change in symptoms on top of any placebo effect.
• The authors therefore concluded that oral antihistamine use can result in statistically significant improvement in nasal obstruction in people with persistent allergic rhinitis.