In random order , they were given the following treatments : ( 1 ) control , no drug ; ( 2 ) nefopam to a target concentration of 0.1 g/mL ; ( 3 ) meperidine to a target concentration of 0.1 g/mL ; and ( 4 ) both nefopam and meperidine at target concentrations of 0.1 g/mL each .