Application of a pharmacokinetics-pharmacodynamics approach to the free propofol plasma levels during coronary artery bypass grafting surgery with hypothermic cardiopulmonary bypass.

OBJECTIVES: The objective of this study was to apply a pharmacokinetics-pharmacodynamics approach to investigate the free propofol plasma levels in patients undergoing coronary artery bypass grafting under hypothermic conditions compared with the off-pump procedure. METHODS: Nineteen patients scheduled for on-pump coronary artery bypass grafting under hypothermic conditions (n=10) or the equivalent off-pump surgery (n=9) were anesthetized with sufentanil and propofol target-controlled infusion (2 µg/mL) during surgery. The propofol concentration was then reduced to 1 µg/mL, and a pharmacokinetics-pharmacodynamics analysis using the maximum-effect-sigmoid model obtained by plotting the bispectral index values against the free propofol plasma levels was performed. RESULTS: Significant increases (two- to five-fold) in the free propofol plasma levels were observed in the patients subjected to coronary artery bypass grafting under hypothermic conditions. The pharmacokinetics of propofol varied according to the free drug levels in the hypothermic on-pump group versus the off-pump group. After hypothermic coronary artery bypass was initiated, the distribution volume increased, and the distribution half-life was prolonged. Propofol target-controlled infusion was discontinued when orotracheal extubation was indicated, and the time to patient extubation was significantly higher in the hypothermic on-pump group than in the off-pump group (459 versus 273 min, p=0.0048). CONCLUSIONS: The orotracheal intubation time was significantly longer in the hypothermic on-pump group than in the off-pump group. Additionally, residual hypnosis was identified through the pharmacokinetics-pharmacodynamics approach based on decreases in drug plasma protein binding in the hypothermic on-pump group, which could explain the increased hypnosis observed with this drug in this group of patients.

Imipenem in burn patients: pharmacokinetic profile and PK/PD target attainment.

Unpredictable pharmacokinetics (PK) in burn patients may result in plasma concentrations below concentrations that are effective against common pathogens. The present study evaluated the imipenem PK profile and pharmacokinetic/pharmacodynamics (PK/PD) correlation in burn patients. Fifty-one burn patients, 38.7 years of age (mean), 68.0 kg, 36.3% total burn surface area (TBSA), of whom 84% (43/51) exhibited thermal injury, 63% inhalation injury and 16% electrical injury (8/51), all of whom were receiving imipenem treatment were investigated. Drug plasma monitoring, PK study (120 sets of plasma levels) and PK/PD correlation were performed in a series of blood samples. Only 250 µl of plasma samples were required for drug plasma measurements using the ultra filtration technique for the purification of biological matrix and quantification using liquid chromatography. Probability of target attainment (PTA) was calculated using a PD target of 40% free drug concentrations above the minimum inhibitory concentration (40%fT>MIC). Significant differences in PK parameters (medians), such as biological half-life (2.2 vs 5.5 h), plasma clearance (16.2 vs 1.4 l h(-1)) and volume of distribution (0.86 vs 0.19 l kg(-1)), were registered in burn patients via comparisons of set periods with normal renal function against periods of renal failure. Correlations between creatinine clearance and total body plasma clearance were also obtained. In addition, the PK profile did not change according to TBSA during sets when renal function was preserved. PTA was >89% for MIC values up to 4 mg l(-1). In conclusion, imipenem efficacy for the control of hospital infection on the basis of PK/PD correlation was guaranteed for burn in patients at the recommended dose regimens for normal renal function (31.1±9.7 mg kg(-1) daily), but the daily dose must be reduced to 17.2±9.7 mg kg(-1) during renal failure to avoid neurotoxicity.