General pharmacological properties of a new non-opiate antitussive: zipeprol (3024 CERM). I. Action on respiratory function and acute toxicity.

1-(2-Methoxy-2-phenyl)-ethyl-4-(2-hydroxy-3-methoxy-3-phenyl)-propyl-iperazine-dihydrochloride (zipeprol, Respilene) is a substance of non-phenanthrenic chemical structure. In the cat, it antagonised cough induced by stimulation of the superior laryngeal nerve or by direct mechanical excitation of the sensitive tracheo-bronchial receptors. The efficacy of zipeprol after enteral administration made it possible both to establish good intestinal absorption and to rank it favourably in relation to several major antitussive reference products; codeine, codethyline, dextromethorphan, diphenhydramine and pentoxyverine. The activity of zipeprol was superior or equal to that of all these substances, excdept codeine. The antitussive properties appeared to be due to a central action. Other properties have been demonstrated which suggest at least a supplementary mechanism in the inhibition of cough, in addition to the central action. These consisted of slight antihistamine and anticholinergic properties, marked local-anesthetic potency and bronchospasmolytic activity. This latter property was demonstrated by the inhibition of histamine and serotonin induced bronchospasm in the guinea-pig. In vitro, using human sputum, zipeprol had a mucolytic action, shown by a decrease in sputum vis viscosity and lysis of DNA and AMPS fibrils. In the dog, at high doses, zipeprol unlike codeine, did not inhibit central stimulation of respiration by hypercapnia, in addition no modification of ventilatory dynamics or blood gases was seen. On the basis of these results, zipeprol can be considered as possessing no respiratory depressant effect even in the upper ranges of its antitussive doses.