Relationship between antihistamic activity and plasma level of diphenhydramine
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Plasma levels of diphenhydramine were determined by gas chromatography up to 34 h after oral administration of 50 mg to 6 healthy men. The antihistaminic activity of diphenhydramine was assessed by reduction in the area of wheals induced by intradermal injection of 5 µg histamine hydrochloride. The plasma level of drug and reduction in size of wheal were related in 4 of the 6 subjects, but not in the other two although all six had similar concentrations of the drug in plasma. In two experiments designed to measure psychometric parameters (number facility and a time evaluation test), no relationship was found between plasma levels of diphenhydramine and the performances of the subjects.
Key wordsDiphenhydramine antihistamine plasma level gas chromatographic assay psychometric tests
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