Comparing the effects of Diphenhydramine hydrochloride with Loratadine on isolated trachea of rabbit

Objective: to study and compare the antagonist effects of first generation anti-histamine diphenhydramine hydrochloride with second generation anti-histamine loratadine on isolated trachea of rabbit. design: comparative controlled in vitro experimental study. place and duration of study: this study was conducted at the department of pharmacology and therapeutics,basic medical sciences institute (bmsi),jinnah postgraduate medical center (jpmc) karachi for the period of six months. material and methods: isolated tracheal smooth muscles of twenty four rabbits are used. fresh kreb's bicarbonate nutritional solution was prepared for each subject. isolated tracheal smooth muscles were exposed to standard dilution of histamine,and then they were challenged with serial dilutions (10 -18 mg/ml to 10 -3 mg/ml) of diphenhydramine hydrochloride and loratadine separately,and effects (rate and amplitude of contractions) were recorded by 7b grass polygraph machine. results: diphenhydramine hydrochloride inhibits the rate of histamine induced tracheal contractions ranging from 0.17 to 8.11 % and amplitude from 0.0 to 100 %,while loratadine inhibit the rate of histamine induced tracheal contractions from 0.85 to 10.59 % and amplitude from 6.5 to 76.82 %. conclusion: diphenhydramine hydrochloride found more potent inhibitor of histamine induced contractions on isolated tracheal smooth muscles of rabbit than loratadine. category: basic sciences.