Clinical effects of Chinese herbal medicine for allergic rhinitis: reviews of classical and modern literature

Background: Allergic rhinitis (AR) is an allergen-induced immunoglobulin E mediated inflammatory disease with significant impact on patients’ quality of life and imposes heavy financial burden to the healthcare system. Due to side effects of Western medicine (WM), more patients are seeking solutions from Chinese herbal medicine (CHM). A number of randomised controlled trials (RCTs) have demonstrated that CHM was effective and safe for managing AR. However, the effects and safety of CHM have not been adequately synthesised. This project aimed to provide a comprehensive evaluation on clinical effects and safety of CHM for the treatment of AR. Methods: This project involved three reviews: (1) A systematic review of RCTs for the effects and safety of CHM adhering to the Cochrane Handbook for Systematic Reviews of Interventions and identification of the most frequently used herbs in RCTs; (2) a review of experimental studies of herbs on their mechanisms of actions and toxicology evidence; and (3) data-mining of classically-used herbs used for AR-like signs and symptoms in Zhong Hua Yi Dian and Zhong Guo Ben Cao Quan Shu using principal component analysis (PCA) and hierarchical cluster analysis (HCA). Results: The Review 1 included 62 RCTs involving 8,470 participants. CHM, used orally as alone or adjunct therapy, could improve nasal symptoms; particularly CHM combined with co-intervention exerted stronger and prolonged clinical effects in nasal symptom improvement. Findings are limited due to the high/unclear risk of bias and substantial heterogeneity. No major side effects were reported across all the included studies. The most commonly used herbs identified were Huang Qi, Fang Feng, Xin Yi, Cang Er Zi and Xi Xin. These five CHMs were further investigated in the Review 2. They possess characteristics of anti-inflammatory, anti-allergic, analgesic, antinociceptive, anti-oxidative, anti-proliferative, anti-viral, anti-asthmatic, anti-bacterial, anti-gastric, anti-vascular and cardiovascular, anxiolytic and muscle relaxant effects as well as immunoregulatory effects. Toxicity of Cang Er Zi and Xi Xin underscored the dangers of renal failures and carcinomas associated with dosage-related response. The Review 3 in the classic literature included 1,687 articles and analysed 294 articles which were associated with 11 AR-like signs and symptoms. A sum of 163 herbs was identified for their management. PCA stated two groups of herbs may have common nature in managing AR-like signs and symptoms: Component 1 herbs included Xi Xin, Xin Yi, Bai Zhi, Bai Bu, Cang Er Zi, Chuan Xiong, Fang Feng, Huang Qi, Gua Di, Bo He and Bai Zhu; and Component 2 herbs were Chuan Xiong, Bai Xian Pi, Gua Di and Huang Qi. HCA also cast Xi Xin as one of the outliers along with Xin Yi. The results from the systematic review need to be interpreted with caution due to limited number of included studies in each comparison with associated high/unclear risk of bias and substantial heterogeneity. Seven common herbs (including Huang Qi, Fang Feng, Xin Yi, Bai Zhi, Cang Er Zi, Gan Cao and Xin Xi) identified from modern clinical studies and classical literature may be considered for AR management in future clinical practice and research