Dissociation between the anti-anaphylactic and the anti-histaminic actions of ketotifen

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Abstract
Ketotifen is a compound with strong antianaphylactic and anti-histaminic properties both in experimental animals and man. In this paper pharmacological experiments are presented which show that these two activities are independent. In the rat, the two actions of ketotifen differ markedly in their time course. The ability of ketotifen to prevent a passive cutaneous anaphylactic reaction is of short duration and is already abolished at times when the compound still fully prevents the cutaneous reaction to histamine. Two antihistamines, clemastine and mepyramine, were compared with ketotifen. All three compounds prevented the wheal and flare induced by intracutaneous administration of histamine, but only ketotifen also prevented passive cutaneous anaphylaxis. Accordingly, concomitant administration of the anti-histamine clemastine with ketotifen resulted in enhanced histamine-blocking effects but did not influence the antianaphylactic action of ketotifen. Finally, clemastine and mepyramine differed from ketotifen in their activities in a model of anaphylactically-induced bronchospasm. Ketotifen prevented the bronchospasm, dyspnea and respiratory arrest in dose-dependent fashion, while the two reference antihistamines were virtually inactive.