Cardiovascular and some respiratory effects of high doses of alfentanil in dogs.

The cardiovascular and some respiratory effects of alfentanil, a potent and short-acting morphinomimetic, were studied in conscious (n = 6) and anaesthetized, artificially ventilated dogs (n = 7). The compound was injected intravenously in increasing doses of 12.5, 12.5, 25, 50, 100, 200, 400 and 800 micrograms X kg-1 in the conscious dogs and of 0.16, 0.32, 0.64, 1.25, 2.5 and 5 mg X kg-1 in the anaesthetized animals. In the conscious dogs, the heart rate decreased significantly reaching a maximum decrease after the injection of 400 micrograms X kg-1 X PCO2 and arterial and venous lactate concentrations increased, while PO2, pH and base excess decreased significantly. At higher dose levels (100-400 micrograms X kg-1) short periods of convulsions were seen. The most pronounced change in the anaesthetized dogs was a significant fall in LVdP/dt max and LV dP/dt max/P, associated with a rise in left ventricular end-diastolic pressure following the injection of 5 mg X kg-1, suggesting negative inotropic properties at this high dose level. Most of the animals showed A-V dissociations which disappeared at higher doses. All animals survived. These findings indicate that alfentanil is a safe analgesic as far as the effects on the cardiovascular system are concerned. High doses are tolerated well, especially when the animals are artificially ventilated. The short periods of convulsions, seen only in the awake dogs, may have been facilitated by the low PO2 levels reached (median value: 9 kPa).