Respiratory depression following single and repeated doses of pentazocine and pethidine.

Pentazocine and pethidine have been compared in the dose ratio 45:75 for their depression of respiration in normal subjects. The respective additive actions of the two drugs were investigated by comparing the effects of a single dose with those of two repeated half-doses. Some degree of ventilatory depression was found consistently. A first half-dose of pentazocine 22.5 mg had a greater effect than a first half-dose of pethidine 37.5 mg, but a second half-dose of pentazocine had a smaller additive effect. The results support existing evidence that a "ceiling" for respiratory depression is attained at a relatively low dosage of pentazocine.