Nefopam HCl interaction study with eight other drugs.

A controlled clinical trial was undertaken to determine potential for drug interaction of nefopam HCl, a new analgesic, with eight other widely used compounds. Nefopam HCl was administered in combination with these drugs and placebo to forty-five healthy volunteer subjects in nine groups of five subjects each. Possible drug interactions were detected by the occurrence of side-effects and interference with bioavailability of the new analgesic, also by changes in vital signs or in various laboratory tests. Results indicated no statistically significant differences in these parameters between the nefopam HCl-placebo regimen and the other eight combinations. Despite this, there were substantial clinical differences in the intensity and incidence of side-effects with combinations of codeine, pentazocine and propoxyphene. These differences warrant further study. Serum nefopam HCl levels were significantly higher on Day 3 than on Day 1, indicating no defect in bioavailability due to drug interaction. Overall, results of this study support the feasibility of concomitant use of these eight drugs with nefopam HCl for short treatment periods.