THE RESPIRATORY EFFECTS OF MORPHINE, CODEINE AND RELATED SUBSTANCES I. THE EFFECT OF CODEINE, ISOCODEINE, ALLOPSEUDOCODEINE AND PSEUDOCODEINE ON THE RESPIRATION OF THE RABBIT

¹ From the Laboratory of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan

Codeine, isocodeine, pseudocodeine and allopseudocodeine have been compared as to their effectiveness in decreasing the rabbit's respiratory rate, minute volume and sensitivity to stimulation by carbon dioxide. The drugs were injected subcutaneously. The minimum doses (milligrams per kilogram of the base) required to decrease respiration are (a) codeine 1.6 to 2.4; (b) isocodeine 2.6 to 3.9; (c) pseudocodeine 76 to 98. Allopseudocodeine hydrochloride does not decrease respiratory activity at less than the convulsant dose. At doses above 10 mgm. per kilogram isocodeine is more effective than codeine in depressing respiration due to the convulsant action of the latter.