Respiratory effects of a new opiate analgesic, R 39209, in the rabbit: comparison with fentanyl.

The respiratory effects of R 39209, a new short-acting analgesic, were studied and compared with those of fentanyl, in the rabbit. Minute volume, respiratory frequency and pH, PCO2 and standard bicarbonate of arterialized venous blood were measured. R 39209 had an earlier peak effect and shorter duration of action then fentanyl, but otherwise the respiratory effects of the two-drugs were similar. Fentanyl was between 2 and 3.5 times more potent than R 39209. Repeated doses of R 39209 produced reproducible peak effects even when only 10 min was allowed between administrations.