Pharmacokinetics and efficacy of ropivacaine in Chinese patients following intra-articular administration.

Objective: The purpose of the present study was to investigate the pharmacokinetics and efficacy of ropivacaine in Chinese patients by intra-articular administration after arthroscopic knee surgery, in order to assess the safety and efficacy.
Patients and Methods: 21 ASA I-II patients received a single-dose of ropivacaine 150 mg in a 20 ml intra-articular injection at the end of surgery. Plasma samples were collected prior to and after ropivacaine administration. Plasma concentrations of ropivacaine were measured by HPLC. Pharmacokinetic parameters were calculated using noncompartmental analysis. Population pharmacokinetic modeling was performed to yield estimates of clearance, volume of distribution, and absorption rate constant. An analysis of covariates on the pharmacokinetic parameters was also carried out. Pain assessments were made using a verbal rating scale at intervals of 2, 4, 8, 12, 24, 36, 48 and 72 hours after surgery.
Results: The results show that the peak plasma concentrations occurred at an average of 0.93 ± 0.56 h (0.25 - 2 h), with a mean of 0.91 ± 0.4 mg/l (range 0.35 - 1.54 mg/l). The peak plasma concentrations and the times to reach the peak plasma concentration exhibited a marked variability among the subjects. All concentrations were well below the estimated toxic threshold (2.2 mg/l). No patient experienced adverse events that may have been related to ropivacaine administration. The intra-articular use of ropivacaine provided excellent control of pain after knee arthroscopy.
Conclusion: Ropivacaine 150 mg provided satisfactory postoperative pain relief and can be safely administered by intraarticular injection in Chinese patients after arthroscopic knee surgery and the pharmacokinetic profiles of ropivacaine exhibited marked variability among the subjects. The high variability of pharmacokinetic profiles in this study may be caused by gender and body weight.