Comparison between cetirizine and terfenadine: time-response study.

Six young healthy volunteers were used as experimental models to study the efficacy of cetirizine 10 mg and terfenadine 60 mg with regard to the onset of action and duration of the peripheral antihistaminic effect (cutaneous activity). For this purpose, 10 micrograms of histamine were used administered as intradermal injection at the internal border of the forearm at times 0', 30', 60', 90', 120', 180', 240', 360', 480' and 24 h after the intake of the drug, with a minimum interval of 7 days between one drug and the other. The inhibition of the cutaneous activity of histamine was assessed by planimetry of the papule transferred to adhesive paper. Both antihistamines were well tolerated by the oral route and our patients did not refer any anticholinergic side effects nor sedation, which are classically described in relation to first generation anti-H1 drugs. When comparing both antihistamines as to their ability to inhibit the response, there are no differences between them at 30', but from this time point up to 24 h cetirizine inhibits significantly more than terfenadine the response to histamine; cetirizine achieves its maximal effect at 180', while terfenadine does so at 240'; both drugs maintain their maximal effect antil 480' and, as was previously mentioned, at these doses cetirizine shows a higher percentage of inhibition than does terfenadine at equal time points.