The Significance of Lipoproteins in Serum Binding Variations of Propofol

The effects of cardiovascular and orthopaedic surgery on vitamin concentrations: a narrative review of the literature and mechanisms of action

Given the rise in worldwide chronic diseases, supplemented by an aging population, the volume of global major surgeries, encompassing cardiac and orthopedic procedures is anticipated to surge significantly. Surgical trauma can be accompanied by numerous postoperative complications and metabolic changes. The present review summarized the results from studies assessing the effects of orthopedic and cardiovascular surgery on vitamin concentrations, in addition to exploring the possible mechanisms associated with changes in concentrations. Studies have revealed a potentially severe depletion in plasma/serum concentrations of numerous vitamins following these surgeries acutely. Vitamins C, D and B1 appear particularly vulnerable to significant depletions, with vitamin C and D depletions consistently transpiring into inadequate and deficient concentrations, respectively. The possible multifactorial mechanisms impacting postoperative vitamin concentrations include changes in hemodilution and vitamin utilization, redistribution, circulatory transport and absorption. For a majority of vitamins, there has been a lack of investigation into the effects of both, cardiac and orthopedic surgery. Additionally, studies were predominantly restricted to short-term postoperative investigations, primarily performed within the first postoperative week of surgery. Overall, results indicated that further examination is necessary to determine the severity and clinical significance of the possible depletions in vitamin concentrations that ensue cardiovascular and orthopedic surgery.

Influence of propofol dose and blood components on duration of electrical seizures in electroconvulsive therapy

Background and objectives

Propofol is commonly employed as a hypnotic agent to perform electroconvulsive therapy, but it exhibits also anticonvulsant properties. The main objective was to study the effect of the weight-adjusted dose of propofol on duration of the electrical seizure. Secondary objectives were to study the effect of absolute dose of propofol on duration of electrical seizure, the effect of both absolute and weight-adjusted doses on values of bispectral index, and the influence of blood chemistry on anticonvulsant effect.

Methods

After approval of the Institutional Review Board, a retrospective chart review was performed of all patients who underwent at least one electroconvulsive therapy session. Multiple lineal regression analysis adjusted for potential confounders was employed to explore the effect of propofol dosage on values of bispectral index and on duration of seizure; bivariate correlation analyses were previously performed to identify variables fulfilling confounding criteria, specifically values of Spearman's rho >0.10. Results of regression analysis were expressed as B coefficient with its 95% confident interval.

Results

76 patients received 631 acute phase sessions. Propofol showed a statistically significant negative effect on duration of seizure (specifically a reduction of 4.081 s for every mg.kg⁻¹ of propofol; CI95%: −7906 to −0.255, p = 0.037) but not on bispectral index values. Slight anemia and hypoalbuminemia were very infrequent conditions, and the anticonvulsant effect was not influenced by these parameters.

Conclusions

Propofol weight-adjusted dose is negatively related to duration of seizures. It should be carefully titrated when employed to perform electroconvulsive therapy.

[Influence of propofol dose and blood components on duration of electrical seizures in electroconvulsive therapy]

BACKGROUND AND OBJECTIVES

Propofol is commonly employed as a hypnotic agent to perform electroconvulsive therapy, but it exhibits also anticonvulsant properties. The main objective was to study the effect of the weight-adjusted dose of propofol on duration of the electrical seizure. Secondary objectives were to study the effect of absolute dose of propofol on duration of electrical seizure, the effect of both absolute and weight-adjusted doses on values of bispectral index, and the influence of blood chemistry on anticonvulsant effect.

METHODS

After approval of the Institutional Review Board, a retrospective chart review was performed of all patients who underwent at least one electroconvulsive therapy session. Multiple lineal regression analysis adjusted for potential confounders was employed to explore the effect of propofol dosage on values of bispectral index and on duration of seizure; bivariate correlation analyses were previously performed to identify variables fulfilling confounding criteria, specifically values of Spearman's rho >0.10. Results of regression analysis were expressed as B coefficient with its 95% confident interval.

RESULTS

76 patients received 631 acute phase sessions. Propofol showed a statistically significant negative effect on duration of seizure (specifically a reduction of 4.081s for every mg.kg^-1 of propofol; CI95%: -7906 to -0.255, p=0.037) but not on bispectral index values. Slight anemia and hypoalbuminemia were very infrequent conditions, and the anticonvulsant effect was not influenced by these parameters.

CONCLUSIONS

Propofol weight-adjusted dose is negatively related to duration of seizures. It should be carefully titrated when employed to perform electroconvulsive therapy.

The bioanalytical challenge of determining unbound concentration and protein binding for drugs

Knowledge regarding unbound concentrations is of vital importance when exploring the PK and PD of a drug. The accurate and reproducible determination of plasma protein binding and unbound concentrations for a compound/drug is a serious challenge for the bioanalytical laboratory. When the drug is in equilibrium with the binding protein(s), this equilibrium will shift when physiological conditions are not met. Furthermore, the true unbound fraction/concentration is unknown, and there are numerous publications in the scientific literature reporting and discussing data that have been produced without sufficient control of the parameters influencing the equilibrium. In this Review, different parameters affecting the equilibrium and analysis are discussed, together with suggestions on how to control these parameters in order to produce as trustworthy results for unbound concentrations/fractions as possible.

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.

In vitro release of propofol and binding capacity with regard to plasma constituents

PURPOSE

New evidence suggests that the anesthetic effect of parenteral propofol emulsions varies between commercial preparations. We examined and compared different propofol preparations to determine propofol release and binding capacity with regard to plasma lipoproteins and albumin.

METHODS

We created a novel assay consisting of microtiter plates coated with either low-density lipoprotein (LDL) or albumin to analyze propofol binding kinetics. Using high performance liquid chromatography (HPLC), we measured propofol release from the oily phase and the corresponding amount of propofol bound to the plates in a time-dependent manner and at equilibrium conditions attained after 30 min of incubation at 37 degrees C. The concentrations of free propofol in the aqueous phase of different propofol preparations - Diprivan, and the generic formulations Propofol "Fresenius" (1% and 2% propofol) and Propofol-Lipuro - were analyzed using ultracentrifugation or dialysis for phase separation. Finally, we investigated the effect of isolated lipoprotein fractions on propofol release.

RESULTS

Propofol bound to LDL-coated plates with approximately twofold higher affinity than to albumin-coated plates. No significant differences in total propofol release were observed between preparations. Moreover, similar amounts of free propofol were observed in the aqueous phase of all products tested (1% propofol preparations: 18 microg/ml; 2% propofol preparations: 35 microg/ml), except for the medium-chain and long-chain triglyceride (MCT/LCT) preparation studied, in which the concentration of free propofol was lower. Lipoproteins had no effect on propofol release, except for high-density lipoprotein (HDL), which triggered almost 100% release from the oily phase at HDL concentrations above 1000 microg/ml.

CONCLUSIONS

No differences were observed between the binding/release capacity and lipoprotein interactions of any of the propofol preparations tested. We propose that clinical observations of inconsistent propofol activity are related to variations in the lipoprotein profile, enzyme activity or genetic disorders of individual patients, rather than to the propofol preparation itself.