Pharmacokinetics of rocuronium bromide in obese female patients

Following administration of 0.6 mg kg(-1) rocuronium, the pharmacokinetics and the pharmacodynamics were studied in six obese and six control (normal weight) patients receiving balanced anaesthesia. Twelve gynaecological pati ents were allocated into two groups, according to body mass index (normal w eight: body mass index: 20-24, obese weight: body mass index > 28). Venous plasma concentrations were determined by high-pressure liquid chromatograph y before administration of rocuronium, at 1, 2, 4, 6, 8, 10, 15, 20, 25, 30 , 35, 40, 48, 60, 75, 120, 180, 240, 300, 360 and 420 min after administrat ion of rocuronium and at recovery of single twitch to 25% and 75% of contro l twitch height. Onset time was shorter (NS) in the obese compared with nor mal weight (obese weight: 65 +/- 16, normal weight: 100 +/- 39 s, mean +/- SD). Duration 25% (obese weight: 29.5 +/- 5.3, normal weight: 28.4 +/- 5.3 min) and spontaneous recovery time (obese weight: 12.6 +/- 2.7, normal weig ht: 12.5 +/- 2.3 min) did not show any differences between the two groups. The pharmacokinetics of rocuronium were comparable in the two groups. The v olume of distribution at steady state Vss (mL kg(-1)) was 208 +/- 56 in nor mal weight and 169 +/- 37 in obese weight. Distribution (T1/2 alpha) and el imination half-life (T1/2 beta) as well as mean residence time were 15.6 +/ - 3.7, 70.3 +/- 23.9 and 53.2 +/- 9.8 min in normal weight and 16.9 +/- 3.8 , 75.5 +/- 25.5 and 51.1 +/- 18.9 min in obese weight, respectively. Also, no differences were observed in plasma clearance (3.89 +/- 0.58 in normal w eight and 3.62 +/- 1.42 mL kg(-1) min(-1) obese weight). This study indicat es that the pharmoacodynamics and pharmacokinetics of rocuronium are in fem ale patients not altered by obesity.