ANTAGONISM BY CAFFEINE OF THE RESPIRATORY EFFECTS OF CODEINE AND MORPHINE

¹ Departrnent of Anesthesia, Stanford University Medical School, Palo Alto, California
² Memorial Hospital, Department of Anesthesiology and the Anesthesiology Section, Division of Experimental Surgery and Division of Clinical Investigation, Sloan-Kettering Institute for Cancer Research, New York, N. Y.

A double-blind factorial study has been carried out to determine the respiratory effects of morphine, codeine, caffeine and combinations of caffeine and these narcotics in terms of the alveolar ventilation-alveolar P_CO2 response curve. No significant respiratory effect of caffeine alone in doses up to 250 mg, administered intramuscularly, was detected. Ten mg of morphine produced significantly more respiratory depression than 60 mg of codeine intramuscularly. However, 62.5 mg and 125 mg of caffeine administered simultaneously with 10 mg of morphine or 60 mg of codeine intramuscularly produced significant antagonism of the respiratory depression. The regression slope for the combinations was not significantly different from a straight line nor was there a significant difference between the slopes of codeine plus caffeine or morphine plus caffeine.