SIMULTANEOUS RESPIRATORY MINUTE VOLUME AND TOOTH PULP THRESHOLD CHANGES FOLLOWING CHRONIC ADMINISTRATION OF LEVORPHAN AND A LEVORPHAN-LEVALLORPHAN MIXTURE IN RABBITS

In chronically injected rabbits, the inclusion of levallorphan with levorphan in a 5:1 ratio delayed the onset of tolerance to the tooth pulp response as compared to levorphan alone. This effect was noted at the 7th day test but was not evident at the 14th or 21st day tests. Crossover tests performed following 7 days of treatment supported this conclusion in that rabbits injected chronically with the levorphan-levallorphan mixture appeared to be less tolerant to levorphan alone than those injected for an equal length of time with levorphan. No evidence of tolerance to respiratory depressant effects was noted after 21 consecutive days of treatment with levorphan, levallorphan or a 5:1 mixture.