Gulshan Ara Jalbani, Madiha Shah, Manzoor Ahmed Unar, Nasreen Kazi, Mahboob Wagan, Riaz Ahmad Sheikh.
Comparing the inhibitory effects of diphenhydramine hydrochloride with cetirizine dihydrochloride on isolated trachea of rabbit.
Pak J Med Health Sci Jan ;5(2):283-7.

Objective: To study and compare the antagonist effects of first generation anti-histamine Diphenhydramine hydrochloride with second generation anti-histamine Cetirizine dihydrochloride on isolated trachea of rabbit. Design: Comparative controlled invitro 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 were used. Fresh Kreb’s nutritional solution was prepared for each subject. Tracheal smooth muscles were exposed to standard dilution of histamine, and then they were challenged with serial dilutions (10-18 to 10-3 gm/ml) of Diphenhydramine hydrochloride and Cetirizine dihydrochloride separately, and effects 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 Cetirizine dihydrochloride inhibit the rate of histamine induced contractions from 0.85 to 12.33 % and amplitude from 0.0 to 82.69 %, as concentration of drugs increased. Conclusion: Cetirizine found more potent antagonistic effects on rate of histamine induced cotractions of isolated tracheal smooth muscles than Diphenhdydramine hydrochloride.While Diphenhdydramine hydrochloride has more potent antagonistic action on amplitudes of histamine induced contractions of isolated tracheal smooth muscles than Cetirizine.

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