PHARMACODYNAMICS, PHARMACOKINETICS, AND INTUBATION CONDITIONS AFTER PRIMING WITH 3 DIFFERENT DOSES OF VECURONIUM

The effects of three different priming doses of vecuronium on pharmaco kinetics, pharmacodynamics, and endotracheal intubation conditions wer e investigated. Forty-two patients were studied in two parts. Ln each part, 21 patients were allocated into three groups (n = 7/group) recei ving 10, 15, or 20 mu g/kg vecuronium as a priming dose, followed by a 50- mu g/kg intubating dose 6 min later. In Part I, Train-of-Four (TO F) ratios and serum concentrations after priming were measured every m inute up to the sixth minute. Onset time [from injection of the intuba ting dose to maximum depression of the first twitch (T1)], clinical du ration (T1 return from maximum block to 25% of control), and recovery index (T1 recovery from 25% to 75% of control) were calculated and ser um concentrations were determined up to 6 h after injection of the int ubating dose. In Part II, the intubating dose was injected 4 min after priming, onset time was determined, and intubation conditions were sc ored. TOF ratio was significantly lower after priming with 20 mu g/kg at the fifth and sixth minutes (0.59 +/- 0.29 and 0.56 +/- 0.32; mean +/- 1 so) compared with the first minute (0.95 +/- 0.1). Recovery inde x was significantly increased after priming with 20 mu g/kg (23.2 +/- 6.6 min, P < 0.05) compared with 10 mu g/kg (9.2 +/- 4.8 min) and 15 m u g/kg (6.7 +/- 1.5 min). Between groups no differences in onset time, clinical duration, and pharmacokinetic variables were found. In Part II, onset time and intubating scores showed no significant differences between the groups. In conclusion, a priming dose of 10 mu g/kg follo wed by a 50-mu g/kg intubating dose 4 min later provides good intubati on conditions within 1-2 min. Larger priming doses are not advantageou s because they result in higher plasma levels and do not hasten onset time more than the smaller dose.