BACKGROUNDZingiber cassumunar Roxb., commonly known as Phlai in Thai, has been used as a traditional medicine in Thailand for the treatment of various diseases, including inflammation and chronic airway disease.

OBJECTIVEThe purpose of this study was to assess the antihistaminic effect of Phlai on skin testing.

DESIGN, SETTING, PARTICIPANTS AND INTERVENTIONThis was a randomized, open-label, three-way crossover study. Twenty allergic rhinitis (AR) patients were enrolled. In randomized sequence, patients received a single dose of Phlai capsules (100 or 200 mg) or loratadine (10 mg) with a washout period of 1 week between each treatment.

MAIN OUTCOME MEASURESSkin prick testing for histamine and common aeroallergen (house dust mite) were performed before treatment and after 1, 2, 3, 4, 6, 8, 12 and 24 hours of treatment. The main treatment outcomes were the mean wheal and flare responses to the skin prick test after treatment.

RESULTSBoth 100 mg and 200 mg Phlai doses suppressed wheal and flare responses to house dust mite allergen, but only 200 mg of Phlai capsules significantly suppressed wheal and flare responses to histamine. Repeated measures analysis of variance showed that loratadine caused more wheal and flare suppression than Phlai capsules in responses to the histamine skin prick test. However, there were no significant differences among the effects of 100 mg Phlai capsules, 200 mg Phlai capsules and loratadine in suppression of wheal and flare induced by the mite skin prick test. Both doses of Phlai were well-tolerated with no adverse events.

CONCLUSIONBoth 100 mg (compound D 4 mg) and 200 mg (compound D 8 mg) Phlai capsules, when taken as a single therapeutic dose, inhibited skin reactivity to histamine and mite skin prick tests in AR patients.

TRIAL REGISTRATIONThai clinical trial registry (TCTR20160510001).