Effect of zopiclone and diazepam on ventilatory response in normal human subjects

The effects of equipotent, single intravenous doses of zopiclone (7.5 mg) and diazepam (10 mg) on ventilatory responses in healthy volunteers (aged 40 to 60 years) were investigated in a randomized, double-blind cross-over study. Drug injections and subsequent tests were separated by a washout period of at least 3 days. The effects on ventilatory responses were evaluated by measuring nonstimulated tidal volume, breathing frequency, and minute ventilation before and after injection of the test medications. The PO2, PCO2, pH, and base excess of arterial capillary blood, as well as blood pressure and heart rate, were measured during the test sessions. A classical rebreathing Krogh spirometer test was carried out starting with a 7% CO2 level. Total ventilation was calculated for the rebreathing period. The intravenous administration of 10 mg of diazepam induced a moderate but significant reduction in the CO2-stimulated ventilatory responses in normal subjects. This effect was not observed after intravenous injection of 7.5 mg zopiclone. Zopiclone induced an increase in respiratory frequency. Both substances elicited a similar moderate decrease in arterial blood pressure.