The significance of lipoproteins in serum binding variations of propofol

The Influence of Differences in Solvents and Concentration on the Efficacy of Propofol at Induction of Anesthesia

Background. Propofol is a popular intravenous anesthetic and varieties of formulations were produced from different laboratories. The present study compared efficacy of propofol of different laboratories and different concentrations (1 and 2%) during induction of anesthesia. Methods. Seventy-five scheduled surgical patients were randomly allocated into three groups. The patients of group D1 received AstraZeneca Diprivan 1% (Osaka, Japan) at a rate of 40 mg kg⁻¹ h⁻¹. Group M1 was given 1% Maruishi (Maruishi Pharmaceutical, Osaka, Japan) and group M2 was given 2% formulation at the same rate of propofol. Achieving hypnosis was defined as failure to open their eyes in response to a verbal command and the venous blood sample was withdrawn. Results. The hypnotic doses of M2 were significantly larger (D1: 91.4 ± 30.9, M1: 90.7 ± 26.7, and M2: 118.4 ± 40.2 mg, resp. (mean ± SD). p < 0.005). Age and gender were selected as statistically significant covariates using general linear model-ANOVA. The blood concentration showed no significant difference among the groups (3.73 ± 2.34, 4.10 ± 3.04, and 4.70 ± 2.12 μg mL⁻¹, resp.). Conclusion. The required dose of propofol was different among the formulations; however, the serum concentration showed no significant difference. This trial is registered with UMIN Clinical Trial Registry: UMIN000019925.

A two-compartment effect site model describes the bispectral index after different rates of propofol infusion

Different estimates of the rate constant for the effect site distribution (k(e0)) of propofol, depending on the rate and duration of administration, have been reported. This analysis aimed at finding a more general pharmacodynamic model that could be used when the rate of administration is changed during the treatment. In a cross-over study, 21 healthy volunteers were randomised to receive a 1 min infusion of 2 mg/kg of propofol at one occasion, and a 1 min infusion of 2 mg/kg of propofol immediately followed by a 29 min infusion of 12 mg kg(-1) h(-1) of propofol at another occasion. Arterial plasma concentrations of propofol were collected up to 4 h after dosing, and BIS was collected before start of infusion and until the subjects were fully awake. The population pharmacokinetic-pharmacodynamic analysis was performed using NONMEM VI. A four-compartment PK model with time-dependent elimination and distribution described the arterial propofol concentrations, and was used as input to the pharmacodynamic model. A standard effect compartment model could not accurately describe the delay in the effects of propofol for both regimens, whereas a two-compartment effect site model significantly improved the predictions. The two-compartment effect site model included a central and a peripheral effect site compartment, possibly representing a distribution within the brain, where the decrease in BIS was linked to the central effect site compartment concentrations through a sigmoidal E(max) model.

Effects of Propofol and Midazolam on Lipids, Glucose, and Plasma Osmolality during and in the Early Postoperative Period Following Coronary Artery Bypass Graft Surgery: A Randomized Trial

It is not clear how levels of serum lipids and glucose and plasma osmolality change during propofol infusion in the pre- and postoperative period of coronary artery bypass graft surgery (CABG). This prospective, randomized, controlled trial evaluated changes in these parameters during propofol or midazolam infusion during and in the early postoperative period following surgery. Twenty patients undergoing CABG were randomized preoperatively into two groups: 10 patients received propofol (induction 1.5 mg/kg, maintenance 1.5 mg kg(-1) h(-1)) and 10 patients received midazolam (induction 0.5 mg/kg, maintenance 0.1 mg kg(-1) h(-1)). Both groups also received fentanyl (induction 20 mug/kg, maintenance 10 microg kg(-1)). Serum lipids, glucose, and plasma osmolality were measured preinduction, precardiopulmonary bypass, at the end of cardiopulmonary bypass, at the end of surgery, and 4 and 24 h postoperatively. In the propofol group, we observed a significant increase in triglycerides and very low-density lipoprotein levels 4 h postoperatively. In the midazolam group, we observed a significant decrease in low-density lipoprotein, cholesterol at the end of cardiopulmonary bypass, end of surgery, and 4 and 24 h postoperatively and significant increase in osmolality at the end of cardiovascular bypass. Changes in glucose levels did not differ significantly different between the two groups. In patients with normal serum lipids, glucose, and plasma osmolality undergoing CABG, propofol infusion for maintenance anesthesia is not associated with dangerous changes in serum lipids, glucose, and plasma osmolality compared with midazolam. A propofol infusion technique for maintenance of anesthesia for cardiac surgery where serum lipids and glucose may be of concern could be recommended as an alternative to midazolam.

Influence of intralipid on free propofol fraction assayed in human serum albumin solutions and human plasma

AIM

It is generally assumed that only unbound drugs can reach the site of action by diffusing across the membranes and exerting pharmacological effects by interacting with receptors. Recent research has shown that the percentage of free drugs may depend on the total drug concentration. The aim of the paper is to verify whether the mentioned dependence reported for propofol also takes place in plasma and human serum albumin samples in the presence of intralipid-the medium used as a vehicle for propofol infusions and a parenteral nutrition agent.

METHODS

Artificial plasma samples and human plasma were spiked with intralipid or ethanolic solutions of propofol. The samples were then assayed for free propofol concentration using ultrafiltration and high performance liquid chromatography with fluorimetric detection.

RESULTS

The decrease of the total drug concentration results in free propofol fraction increase, irrespectively of the used type of propofol solvent and sample type. The addition of intralipid causes the lowering of the overall free drug fraction with respect to the samples spiked with ethanolic solutions of the drug.

CONCLUSION

The presence of intralipid does not influence the phenomenon of free propofol fraction rise at low total drug concentration. Such a rise cannot be ignored in clinical conditions when the drug is applied for sedative, antiemetic or other low-dosage purposes.

Disposition and pharmacodynamics of propofol during isovolaemic haemorrhage followed by crystalloid resuscitation in humans

AIMS

The purpose of this study was to estimate the changes in unbound propofol concentration and pharmacodynamics of propofol during isovolaemic haemorrhage followed by crystalloid resuscitation.

METHODS

Ten patients undergoing measure elective surgery were enrolled in this study. Anaesthesia was maintained by 60% nitrous oxide in oxygen, fentanyl 10-20 microg kg-1 and an infusion of propofol at 8 mg kg-1 h-1 until the end of the operation. Radial arterial samples were collected for measurement of propofol concentration just before the start of the operation, and at the point when blood loss was >10 ml kg-1, 20 ml kg-1 and 30 ml kg-1. Cardiac output (CO), haemoglobin values and plasma concentrations of albumin were also determined. Patients were resuscitated with lactated Ringer's solution to maintain a mean arterial blood pressure (+/-20% of prehaemorrhage). Bispectral index (BIS) was measured continuously.

RESULTS

Mean blood pressure, heart rate and CO were well maintained during the operation in all patients. Haemoglobin values and plasma albumin concentrations decreased significantly during surgery. There were no significant differences in total propofol concentrations across the time points. The unbound propofol concentration was increased from 0.10+/-0.040 microg ml-1 to 0.17+/-0.041 microg ml-1 after the haemorrhage of 30 ml kg-1 (P<0.05). BIS was significantly decreased from 47+/-5.9 to 39+/-3.7 (P<0.05) after the haemorrhage of 30 ml kg-1.

CONCLUSIONS

The hypnotic potency of propofol is increased during isovolaemic haemorrhage in crystalloid resuscitated patients even if CO is maintained.

The relationship between bispectral index and targeted propofol concentration is biphasic in patients with major burns

BACKGROUND

Many pathophysiologic alterations in major burns can cause changes in the distribution of, and perhaps response to, drugs commonly used in anesthesia practice. This study was conducted to assess changes in bispectral index (BIS) caused by increasing the target propofol effect-site concentration during a target-controlled infusion (TCI) in major burns.

METHODS

Eighteen patients, ASA physical status 2 or 3, aged from 20 to 55 years old, weighing 50-70 kg, with major burns, scheduled for elective early escharectomy less than a week after injury were recruited. A further 18 ASA physical status class 1 or 2, non-burns, age, sex- and weight-matched adult patients scheduled for elective surgery under general anesthesia were recruited as controls. During anesthesia induction, target propofol effect-site concentrations were increased by increments of 0.5 microg ml(-1) up to 4.5 microg ml(-1). The BIS responses to each target concentration using TCI were compared in both groups.

RESULTS

In the burns group, significantly greater BIS values relating to increasing propofol TCI were noted at deeper anesthesia when compared with controls; at > or =3.5 microg ml(-1); mean BIS remained at a plateau of about 50. Patients with burns had higher cardiac indices, and lower hemoglobin and albumin concentrations than the controls. They consumed more vecuronium to maintain the same degree of neuromuscular blockade than the controls.

CONCLUSIONS

In major burns, the final biphasic BIS responses appeared to be determined by numerous other variables such as BIS algorithm, TCI performance, and altered propofol pharmacokinetics and pharmacodynamics. According to our results the importance of an individually tailored approach, including careful anesthetic titration, based upon the patient's clinical condition and responses can not be overemphasized.

Influence of formulation on propofol pharmacokinetics and pharmacodynamics in anesthetized patients

BACKGROUND

In anesthesia with propofol, variability persists besides sophisticated effect targeting. Drug formulation may be another factor. We have analyzed, retrospectively, the pharmacokinetics (PK) and pharmacodynamics (PD) in monitored surgery patients anesthetized with one each of five formulations of propofol.

METHODS

Propofol 1% ('form' 1: Diprivan(Zeneca Limited, Macclesfield, UK), 2: Recofol(Schering Espana, Madrid, Spain), 3: Ivofol(Juste, Madrid, Spain), 4: Propofol Abbott (Abbott Laboratories, Madrid, Spain), 5: Fresenius (Fresenius Kabi Espana, Barcelona, Spain)) was administered to 77 ASA I-II patients of age [mean (range) 44 (18-65) years]. Induction of anesthesia was with varying propofol doses up to endpoints of either 60 on the Bispectral Index system (BIS) in group I (n = 48, model development) or standard clinical signs in group II (n = 29, validation). Maintenance was with three 10-min infusions of 10, 8 and 6 mg kg(-1) h(-1). Three blood samples were obtained from each subject, immediately after induction, and at 15 and 30 min on maintenance, with BIS and hemodynamic variables recorded at these times also. Total and free blood concentrations (Cb) of propofol were determined with HPLC. Pharmacokinetic and PD models with link equilibration rate ke0, were studied with a mixed-effects procedure (NONMEM).

RESULTS

The induction dose (group I) showed large interindividual variability [mean (range) 163 (90-290 mg)] that correlated significantly with age, basal systolic blood pressure and formulation. The PK of propofol (basic model) was described by a one-compartment model with (typical value [interindividual coefficient of variation percent (CV%)]) CL=2.30 l min(-1) (27%) and V=8.40 l (80%). Weight (WT) and formulation, within NONMEM, were found to be significant covariates for CL and V, reducing their CV% to 25% and 74%, respectively. The final PK/PD model, which includes formulation, showed a 50% reduction in the CV% for both the ke0 and the residual error. This PK/PD model was validated in group II with 33% precision and no bias.

CONCLUSION

The PK and PD are not equal for all formulations, which contributes to an increase in variability of the observed effect.

Long-term sedation with propofol 60 mg ml(-1) vs. propofol 10 mg(-1) ml in critically ill, mechanically ventilated patients

BACKGROUND

Hypertriglyceridaemia is the main cause of therapeutic failure during propofol use in long-term sedated mechanically ventilated patients. Propofol 60 mg ml(-1) has been developed to reduce fat and volume load for the critically ill patient. The purpose of the study was to compare the effectiveness of sedation, achievability of effective concentrations and the effects on serum lipid concentrations of propofol 60 mg ml(-1) vs. propofol 10 mg ml(-1) for long-term sedation in critically ill patients.

METHODS

In this randomized, open, prospective study, 20 critically ill, mechanically ventilated patients who required sedation for a minimum of 48 h received propofol 60 mg ml(-1) or propofol 10 mg ml(-1) in doses as required during 2-5 days.

RESULTS

No differences between propofol 60 mg ml(-1) and propofol 10 mg ml(-1) were observed in the effectiveness of sedation using the Ramsay Sedation score and the Subjective Sedation score, nor in relation to the propofol concentrations. Between the two groups, there were no significant differences in the daily propofol dose, number of daily infusion rate adjustments or need for additional sedatives. Mean serum triglyceride concentrations were higher in the propofol 10 mg ml(-1) group compared with the propofol 60 mg ml(-1) group [5.26 (3.19) vs. 3.22 (2.05) mmol l(-1), P > 0.05][mean (SD)]. Patients in the propofol 10 mg ml(-1) group received more fat from the propofol infusion than from the propofol 60 mg ml(-1) group [53.2 (29.6) vs. 10.0 (4.7) % compared with fat from nutrition, respectively]. A significant relationship was observed between the daily total fat dose and the serum triglyceride concentration (r2 = 0.32, P < 0.001), whereas there was no significant correlation between the daily propofol dose and the serum triglyceride concentration.

CONCLUSION

Propofol 60 mg ml(-1) is a useful alternative to propofol 10 mg ml(-1) for the long-term sedation of critically ill patients. Sedation with propofol 60 mg ml(-1) reduces fat and volume load by 83%, which reduces the risk of hypertriglyceridaemia.

Prediction of unbound propofol concentrations in a diabetic population

Propofol is a short-acting general intravenous anesthetic characterized by a wide interindividual variability in the response after the same dose. Its binding to serum proteins exceeds 98%, so small changes in protein concentrations can be amplified in the unbound fraction of the drug and hence possibly in the effect. It is then likely that part of the variability in the response could be attributed to differences in protein levels among individuals and particularly among those with pathologies such as diabetes. The aim of this study was to establish predictive regression models in a diabetes mellitus (DM) population between unbound:bound propofol ratios and demographic and biochemical indices. Unbound:bound propofol ratios can be routinely obtained in the clinic as opposed to the free fraction of the drug. In DM patients (30 women and 37 men aged between 17 and 78 y) with mellitus type 1 (n = 37) and type 2 (n = 30) diabetes, the authors measured the lipoproteins (HDL, LDL, and VLDL), cholesterol, triglycerides, albumin, alpha1-acid glycoprotein (AAG), free fatty acids (FFA), glycosylated hemoglobin, and the unbound fraction (Fu) and the bound/free ratio (B/F) of propofol. A linearized regression model between the above variables--as well as age, sex, and type of diabetes--and Fu was then developed. Patients had blood drawn and sera separated by centrifugation and spiked with propofol to a concentration of 10 microg/mL. The Fu was determined via ultrafiltration. Multiple linear regression analysis was used to identify significant predictor variables of Fu in this population and two models were originated: one with lipoprotein serum concentrations as explanatory variables (Model A) and another that depended on cholesterol and triglycerides (Model B). Both models presented high correlation coefficients (r2 = 0.71 and 0.68, respectively; P < 0.0001), and each was used to predict Fu in an independent group of 15 DM patients of similar characteristics and biochemical indices as the model development group. Bias and precision were for Model A, 0.9% and 7.8%, and for Model B, 3.0% and 8.7%, respectively. Both models were compared with each other and to a naive predictor (the mean) and each was better than the naive model in predicting the unbound fraction of propofol. Model A and model B could be used in estimating Fu of propofol in DM patients based on the more routine clinical measures of lipoprotein serum concentrations or cholesterol and triglyceride levels.