THE SEPARATE AND COMBINED RESPIRATORY EFFECTS OF CHLORPROMAZINE AND MEPERIDINE IN NORMAL MEN CONTROLLED AT 46 mm Hg ALVEOLAR pCO₂

¹ Laboratories of Pharmacology, Schools of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania

A method for artificially controlling alveolar pCO₂ was used to study the time course of changes in respiratory rate, depth and minute volume after intramuscular administration of physiological saline solution (2 ml), chlorpromazine hydrochloride (25 mg/70 kg), meperidine hydrochloride (100 mg/70 kg) and of meperidine together with chlorpromazine in the stated doses. The method employed provided magnification of drug-induced respiratory alterations by preventing the physiological readjustments in alveolar pCO₂ normally associated with changes in alveolar ventilation. The results obtained indicated (a) the time course of a consistent and prominent respiratory depression by meperidine, (b) that chlorpromazine alone produces no consistent respiratory depression but that it may tend to improve tolerance to elevated pCO₂, and (c) that administration of chlorpromazine with meperidine causes respiratory depression greater in degree and duration than produced by meperidine alone. The data obtained are discussed with regard to mechanisms of the observed chlorpromazine-meperidine interaction.