Binding of propofol to blood components: implications for pharmacokinetics and for pharmacodynamics

Development of extended pharmacokinetic models for propofol based on measured blood and brain concentrations

Propofol's pharmacokinetics have been extensively studied using human blood samples and applied to target-controlled infusion systems; however, information on its concentration in the brain remains scarce. Therefore, this study aimed to simultaneously measure propofol plasma and brain concentrations in patients who underwent awake craniotomy and establish new pharmacokinetic model. Fifty-seven patients with brain tumors or brain lesions who underwent awake craniotomy were sequentially assigned to model-building and validating groups. Plasma and brain (lobectomy or uncapping margins) samples were collected at five time-points. The concentration of propofol was measured using high-performance liquid chromatography. Population pharmacokinetic analysis was conducted through a nonlinear mixed-effects modeling program using a first-order conditional estimation method with interactions. Propofol's brain concentrations were higher than its plasma concentrations. The measured brain concentrations were higher than the effect site concentrations using the previous models. Extended models were constructed based on measured concentrations by incorporating the brain/plasma partition coefficient (Kp value). Extended models showed good predictive accuracy for brain concentrations in the validating group. The Kp value functioned as a factor explaining retention in the brain. Our new pharmacokinetic models and Kp value can predict propofol's brain and plasma concentrations, contributing to safer and more stable anesthesia.

Exhaled breath is found to be better than blood samples for determining propofol concentrations in the brain tissues of rats

The correlation between propofol concentration in exhaled breath (CE) and plasma (CP) has been well-established, but its applicability for estimating the concentration in brain tissues (CB) remains unknown. Given the impracticality of directly sampling human brain tissues, rats are commonly used as a pharmacokinetic model due to their similar drug-metabolizing processes to humans. In this study, we measuredCE,CP, andCBin mechanically ventilated rats injected with propofol. Exhaled breath samples from the rats were collected every 20 s and analyzed using our team's developed vacuum ultraviolet time-of-flight mass spectrometry. Additionally, femoral artery blood samples and brain tissue samples at different time points were collected and measured using high-performance liquid chromatography mass spectrometry. The results demonstrated that propofol concentration in exhaled breath exhibited stronger correlations with that in brain tissues compared to plasma levels, suggesting its potential suitability for reflecting anesthetic action sites' concentrations and anesthesia titration. Our study provides valuable animal data supporting future clinical applications.

A comprehensive analysis of intraoperative factors associated with acute-on-chronic kidney injury in elderly trauma patients: blood loss as a key predictor

BACKGROUND

Postoperative acute kidney injury (AKI) is a critical issue in geriatric patients with pre-existing chronic kidney disease (CKD) undergoing orthopedic trauma surgery. The goal of this study was to investigate modifiable intraoperative risk factors for AKI.

METHODS

A retrospective study was conducted on 206 geriatric patients with CKD, who underwent orthopedic trauma surgery. Several variables, including intraoperative blood loss, postoperative hypoalbuminemia, intraoperative blood pressure and long-term use of potentially nephrotoxic drugs, were analyzed.

RESULTS

Postoperative AKI (KIDGO) was observed in 25.2% of the patients. The 1-year mortality rate increased significantly from 26.7% to 30.8% in patients who developed AKI. Primary risk factors for AKI were blood loss (p < 0.001), postoperative hypoalbuminemia (p = 0.050), and potentially nephrotoxic drugs prior to admission (angiotensin-converting enzyme inhibitors, angiotensin-II receptor antagonists, diuretics, antibiotics, NSAIDs) (p = 0.003). Furthermore, the AKI stage negatively correlated with propofol dose per body weight (p = 0.001) and there was a significant association between AKI and the use of cement (p = 0.027). No significant association between intraoperative hypotension and AKI was observed in any statistical test. Femur fracture surgeries showed the greatest blood loss (524mL ± 357mL, p = 0.005), particularly intramedullary nailing at the proximal femur (598mL ± 395mL) and revision surgery (769mL ± 436mL).

CONCLUSION

In geriatric trauma patients with pre-existing CKD, intraoperative blood loss, postoperative hypoalbuminemia, and pre-admission use of potentially nephrotoxic drugs are associated with postoperative AKI. The findings highlight the necessity to mitigate intraoperative blood loss and promote ortho-geriatric co-management to reduce the incidence and subsequent mortality in this high-risk population.

Change of dexmedetomidine and midazolam concentrations by simultaneous injection in an in vitro extracorporeal circuit

PURPOSE

Patient sedation and analgesia are vital for safety and comfort during extracorporeal membrane oxygenation (ECMO). However, adsorption by the circuit may alter drug pharmaco-kinetics and remains poorly characterized. This study is the first to examine the concentrations of DEX and MDZ in the presence of drug-drug interactions using an in vitro extracorporeal circuit system that incorporates a polymer-coated polyvinyl chloride tube, but not a membrane oxygenator.

METHODS AND RESULTS

Nine in vitro extracorporeal circuits were prepared using polymer-coated PVC tubing. Once the circuits were primed and running, either a single drug or two drugs were injected as boluses into the circuit with three circuits per drug. Drug samples were drawn following injection at 2, 5, 15, 30, 60, and 120 min and at 4, 12, and 24 h. They were then analyzed using high-performance liquid chromatography with mass spectrometry. When compared with an injection of DEX alone, the combination of DEX and MDZ is highly changed, with DEX and MDZ affecting the availability of free drugs in the circuit.

CONCLUSIONS

The change of DEX and MDZ concentrations was confirmed by a combination of both drugs as compared with either single-infusion DEX or MDZ in an in vitro extracorporeal circuit. Drug-drug interactions developed between DEX and MDZ through albumin in an extracorporeal circuit; as a result, the unbounded drugs might change in the circuit.

Potential pharmacological confounders in the setting of death determined by neurologic criteria: a narrative review

Guidelines for the determination of death by neurologic criteria (DNC) require an absence of confounding factors if clinical examination alone is to be used. Drugs that depress the central nervous system suppress neurologic responses and spontaneous breathing and must be excluded or reversed prior to proceeding. If these confounding factors cannot be eliminated, ancillary testing is required. These drugs may be present after being administered as part of the treatment of critically ill patients. While measurement of serum drug concentrations can help guide the timing of assessments for DNC, they are not always available or feasible. In this article, we review sedative and opioid drugs that may confound DNC, along with pharmacokinetic factors that govern the duration of drug action. Pharmacokinetic parameters including a context-sensitive half-life of sedatives and opioids are highly variable in critically ill patients because of the multitude of clinical variables and conditions that can affect drug distribution and clearance. Patient-, disease-, and treatment-related factors that influence the distribution and clearance of these drugs are discussed including end organ function, age, obesity, hyperdynamic states, augmented renal clearance, fluid balance, hypothermia, and the role of prolonged drug infusions in critically ill patients. In these contexts, it is often difficult to predict how long after drug discontinuation the confounding effects will take to dissipate. We propose a conservative framework for evaluating when or if DNC can be determined by clinical criteria alone. When pharmacologic confounders cannot be reversed, or doing so is not feasible, ancillary testing to confirm the absence of brain blood flow should be obtained.

Propofol-Bispectral Index (BIS) Electroencephalography (EEG) Pharmacokinetic-Pharmacodynamic Model in Patients With Post-Cerebral Hemorrhage Hydrocephalus

Background. Titrating hypnotic agents for patients who suffer from a cerebral insult is a challenging task. To date there is no real gold standard to precisely quantify electroencephalography (EEG) response in a fashion that could be utilized for patients with post-cerebral hemorrhage hydrocephaly. While we must administer "as per usual" analgesics for noxious stimuli, we have to administer the hypnotic agents more "sparingly" due to lack of objective monitoring. Methods. We compared 15 adult post-cerebral hemorrhage hydrocephalus patients undergoing ventriculo-peritoneal shunt placement with 15 controls matched for gender and approximate age. We set propofol target controlled infusion estimated plasma concentrations (C_p) to gradually reach 4 µg/mL over 4 minutes. To precisely quantify post-cerebral hemorrhage mental dysfunction, we used electronically retrieved bispectral index (BIS) and propofol C_p data points to create individual inhibitory monophasic mathematical model for each patient that incorporates an independent hysteresis "lag" function. Results. In post-cerebral hemorrhage patients C_p-BIS curve, C₅₀ (propofol concentration associated with inhibitory 50% BIS response) cutoff point was significantly shifted to the left by 39%. Whereas before infusion and at stable propofol 4 µg/mL aneurismal surgical sides ipsilateral (75 ± 13, 25 ± 9) and contralateral (73 ± 15, 27 ± 9) mean ± SD BIS values were significantly lower than ipsilateral (95 ± 3, 46 ± 12) and contralateral (94 ± 3, 46 ± 12) matched controls. Conclusions. Using BIS as surrogate marker of propofol hypnotic effect, BIS monitoring in patients with post-cerebral hemorrhage hydrocephaly showed a pattern of change and trend that was similar albeit 39% significantly lower than subjects without.

Polymeric membrane-modified voltammetric sensors for lipophilic analytes with nanomolar detection limit: Key parameters influencing the response characteristics

Thin plasticized PVC membrane-coated glassy carbon working electrodes have been used for the voltammetric measurement of highly lipophilic, electroactive drugs. Compared to conventional working electrodes, these membrane-coated electrodes exhibit remarkable detection limit and selectivity and are less prone to electrode fouling. The unique performance characteristics of these sensors are related to the large partition coefficient of the analyte in the membrane coating where it is oxidized in a non-aqueous membrane phase. To analyze the influence of the key parameters of the response of membrane-coated sensors, we derived theoretical expressions on the voltammetric response of the sensors. In our analysis we considered 1) the partition coefficient (P_mw) of the analyte between the aqueous sample and the organic membrane, 2) the membrane volume to sample volume ratio (V_m/V_w), and 3) the binding constant of constituents in the sample that bind the analyte (K). The results of our theoretical analysis have been tested through voltammetric measurement of highly lipophilic analytes with logP_ow values (logarithm of the partition coefficient between octanol and water) ranging between 0.3 and 7.5. By understanding of the influence of the sensor design parameters on the overall sensor response, these parameters can be tuned for optimized response slope, detection limit, etc., for solving specific analytical tasks.

Volatile Versus Intravenous Anesthetics in Cardiac Anesthesia: a Narrative Review

Purpose of the Review

The present review addresses clinicians and gives an overview about the experimental rationale for pharmacological conditioning associated with volatile anesthetics, opioids, and propofol; the current clinical data; and the technical considerations regarding the clinical routine in cardiac anesthesia.

Recent Findings

Volatile anesthetics have been standard of care for general anesthesia for cardiac surgery, especially while using cardiopulmonary bypass. The 2019 published MYRIAD trial was not able to show a difference in mortality or cardiac biomarkers for volatile anesthetics compared to total intravenous anesthesia (TIVA), raising the question of equivalence with respect to patient outcome.

Summary

Reviewing the literature, the scientific foundation for the belief of clinically relevant conditioning by uninterrupted administration of a volatile anesthetic is weak. TIVA can also be performed safely in patients undergoing cardiac surgery.

Propofol detection for monitoring of intravenous anaesthesia: a review

This paper presents a review of established and emerging methods for detecting and quantifying the intravenous anaesthetic propofol in solution. There is growing evidence of numerous advantages of total intravenous anaesthesia using propofol compared to conventional volatile-based anaesthesia, both in terms of patient outcomes and environmental impact. However, volatile-based anaesthesia still accounts for the vast majority of administered general anaesthetics, largely due to a lack of techniques for real-time monitoring of patient blood propofol concentration. Herein, propofol detection techniques that have been developed to date are reviewed alongside a discussion of remaining challenges.

Common anti-COVID-19 drugs and their anticipated interaction with anesthetic agents

The corona virus disease 2019 (COVID-19) pandemic has till date (26/7/20) affected 1crore 62 lac 73 thousand 638 people globally with almost 6.5 lakh mortalities. COVID-19 has invaded the operation theatre and intensive care unit (ICU) in a short span of 6 months. It appears inevitable that all of us, as anesthesiologists, have to treat COVID-positive patients, either in the ICU or the operation theatre. Many asymptomatic, presumably noninfected people including frontline health care workers are also consuming potential anticorona viral drugs (such as hydroxychloroquine) prophylactically and may present for surgery. Detailed knowledge of which anesthetic and perioperative care drugs can interact with anti-COVID drugs would be very valuable for pre, intra-, and postoperative management of such patients and COVID-19 positive patients requiring intubation, mechanical ventilation, and ICU-sedation. Powered with this knowledge, anesthesiologists and intensivists can minimize the adverse effects of drug interactions. An extensive literature search using different search engines including Cochrane, Embase, Google Scholar, Scopus, and PubMed for all indexed review articles, original articles, case reports, and referenced webpages was performed to extract the most current and relevant literature on drug-drug interactions for clinicians.

Exhaled Propofol Concentrations Correlate With Plasma and Brain Tissue Concentrations in Rats

BACKGROUND

Propofol can be measured in exhaled gas. Exhaled and plasma propofol concentrations correlate well, but the relationship with tissue concentrations remains unknown. We thus evaluated the relationship between exhaled, plasma, and various tissue propofol concentrations. Because the drug acts in the brain, we focused on the relationship between exhaled and brain tissue propofol concentrations.

METHODS

Thirty-six male Sprague-Dawley rats were anesthetized with propofol, ketamine, and rocuronium for 6 hours. Animals were randomly assigned to propofol infusions at 20, 40, or 60 mg·kg·h (n = 12 per group). Exhaled propofol concentrations were measured at 15-minute intervals by multicapillary column-ion mobility spectrometry. Arterial blood samples, 110 µL each, were collected 15, 30, and 45 minutes, and 1, 2, 4, and 6 hours after the propofol infusion started. Propofol concentrations were measured in brain, lung, liver, kidney, muscle, and fat tissue after 6 hours. The last exhaled and plasma concentrations were used for linear regression analyses with tissue concentrations.

RESULTS

The correlation of exhaled versus plasma concentrations (R = 0.71) was comparable to the correlation of exhaled versus brain tissue concentrations (R = 0.75) at the end of the study. In contrast, correlations between plasma and lung and between lung and exhaled propofol concentrations were poor. Less than a part-per-thousand of propofol was exhaled over 6 hours.

CONCLUSIONS

Exhaled propofol concentrations correlate reasonably well with brain tissue and plasma concentrations in rats, and may thus be useful to estimate anesthetic drug effect. The equilibration between plasma propofol and exhaled gas is apparently independent of lung tissue concentration. Only a tiny fraction of administered propofol is eliminated via the lungs, and exhaled quantities thus have negligible influence on plasma concentrations.

In vitro alteration on erythrocytes mechanical properties by propofol, remifentanil and vecuronium

Several studies report flow disturbance and microcirculation disorders upon anesthesia treatment. These alterations are often related to blood rheology changes. In this work, it was attempted to make a detailed description of the alterations in erythrocyte mechanical properties by the action of propofol, remifentanil, and vecuronium. For this, an in vitro study was performed on red blood cell samples from healthy donors incubated with solutions of propofol (4 μg/mL whole blood), remifentanil (10 ng/mL plasma), and vecuronium (0.15 μg/mL plasma). Erythrocyte viscoelastic parameters were determined by octuplicate using a Reómetro Eritrocitario. Also, a Wilcoxon signed rank-test with Yates correction for continuity was performed to analyze the overall alteration in the mechanical properties of erythrocytes. Statistical analysis showed that the three studied anesthetics changed the erythrocyte mechanical properties at different parts of the membrane. These results would imply an interaction of these anesthetics with the erythrocyte membrane. Finally, this could conduce to alterations in microcirculation.

[Effect of pre-administered flurbiprofen axetil on the EC50 of propofol during anesthesia in unstimulated patients: a randomized clinical trial]

BACKGROUND AND OBJECTIVES

Preoperative use of flurbiprofen axetil (FA) is extensively adopted to modulate the effects of analgesia. However, the relationship between FA and sedation agents remains unclear. In this study, we aimed to investigate the effects of different doses of FA on the median Effective Concentration (EC50) of propofol.

METHODS

Ninety-six patients (ASA I or II, aged 18-65 years) were randomly assigned into one of four groups in a 1:1:1:1 ratio. Group A (control group) received 10 mL of Intralipid, and groups B, C and D received 0.5 mg.kg^-1, 0.75 mg.kg^-1 and 1 mg.kg^-1 of FA, respectively, 10 minutes before induction. The depth of anesthesia was measured by the Bispectral Index (BIS). The "up-and-down" method was used to calculate the EC50 of propofol. During the equilibration period, if BIS ≤ 50 (or BIS > 50), the next patient would receive a 0.5 μg.mL^-1-lower (or-higher) propofol Target-Controlled Infusion (TCI) concentration. The hemodynamic data were recorded at baseline, 10 minutes after FA administration, after induction, after intubation, and 15 minutes after intubation.

RESULTS

The EC50 of propofol was lower in Group C (2.32 μg.mL^-1, 95% Confidence Interval [95% CI] 1.85-2.75) and D (2.39 μg.mL^-1, 95% CI 1.91-2.67) than in Group A (2.96 μg.mL^-1, 95% CI 2.55-3.33) (p = 0.023, p = 0.048, respectively). There were no significant differences in the EC50 between Group B (2.53 μg.mL^-1, 95% CI 2.33-2.71) and Group A (p ˃ 0.05). There were no significant differences in Heart Rate (HR) among groups A, B and C. The HR was significantly lower in Group D than in Group A after intubation (66 ± 6 vs. 80 ± 10 bpm, p < 0.01) and 15 minutes after intubation (61 ± 4 vs. 70 ± 8 bpm, p < 0.01). There were no significant differences among the four groups in Mean Arterial Pressure (MAP) at any time point. The MAP of the four groups was significantly lower after induction, after intubation, and 15 minutes after intubation than at baseline (p < 0.05).

CONCLUSION

High-dose FA (0.75 mg.kg^-1 or 1 mg.kg^-1) reduces the EC50 of propofol, and 1 mg.kg^-1 FA reduces the HR for adequate anesthesia in unstimulated patients. Although this result should be investigated in cases of surgical stimulation, we suggest that FA pre-administration may reduce the propofol requirement when the depth of anesthesia is measured by BIS.

Novel Approach for Characterizing Propofol Binding Affinities to Serum Albumins from Different Species

The interaction between the main carrier (serum albumin, SA) of endogenous and exogenous compounds in the bloodstream of different species (human, bovine, canine, rat, rabbit, and sheep) and a general anesthetic agent (propofol, PR) was investigated using an experimental technique (high-performance liquid chromatography) and computational methods (molecular docking, molecular dynamics, sequence, and phylogenetic analyses). The obtained results revealed the differences in the PR binding affinity to various homologous forms of this protein with reliable statistics (R ² = 0.9 and p-value < 0.005), correlating with the evolutionary relationships among SAs from different species. Additionally, the protein conformational changes (root-mean-square deviation ≈ 1.0 Å) and amino acid conservation of binding sites in protein domains were detected, contributing to the SA-PR binding modes. Overall, the outcomes from this study might provide a novel methodology to assess protein-ligand interactions and to gain some interesting insights into drug pharmacokinetics and pharmacodynamics to explain its variations among different species.

Bispectral Index During Maintenance of Total Intravenous Anesthesia: Frequency of Out of Recommended Range and Impact of Patients' Characteristics: A Brief Report

Little is known about respecting the recommended range of bispectral index (BIS) in practice. This exploratory retrospective analysis of 138 robotic surgical patients having received total intravenous anesthesia shows that BIS was between 40 and 60 during 61.3% ± 25.2% (mean ± standard deviation [SD]) of maintenance, >60 during 3.1% ± 5.5%, and <40 during 35.7% ± 26.9%. Burst suppression was present during 17.8% ± 22.2%. Female sex is associated with increased periods of BIS <40 (P = .002) as is body mass index (BMI) <26 (P = .012). Increased age is associated with increase in burst suppression (P = .005). A larger study is required to confirm the role of patients' factors on the number of periods of low BIS.

The effect of cardiac output on the pharmacokinetics and pharmacodynamics of propofol during closed-loop induction of anesthesia

BACKGROUND AND OBJECTIVE

Intraoperative hemodynamic stability is essential to safety and post-operative well-being of patients and should be optimized in closed-loop control of anesthesia. Cardiovascular changes inducing variations in pharmacokinetics may require dose modification. Rigorous investigational tools can strengthen current knowledge of the anesthesiologists and support clinical practice. We quantify the cardiovascular response of high-risk patients to closed-loop anesthesia and propose a new application of physiologically-based pharmacokinetic-pharmacodynamic (PBPK-PD) simulations to examine the effect of hemodynamic changes on the depth of hypnosis (DoH).

METHODS

We evaluate clinical hemodynamic changes in response to anesthesia induction in high-risk patients from a study on closed-loop anesthesia. We develop and validate a PBPK-PD model to simulate the effect of changes in cardiac output (CO) on plasma levels and DoH. The wavelet-based anesthetic value for central nervous system monitoring index (WAV_CNS) is used as clinical end-point of propofol hypnotic effect.

RESULTS

The median (interquartile range, IQR) changes in CO and arterial pressure (AP), 3 min after induction of anesthesia, are 22.43 (14.82-36.0) % and 26.60 (22.39-35.33) % respectively. The decrease in heart rate (HR) is less marked, i.e. 8.82 (4.94-12.68) %. The cardiovascular response is comparable or less enhanced than in manual propofol induction studies. PBPK simulations show that the marked decrease in CO coincides with high predicted plasma levels and deep levels of hypnosis, i.e. WAV_CNS < 40. PD model identification is improved using the PBPK model rather than a standard three-compartment PK model. PD simulations reveal that a 30% drop in CO can cause a 30% change in WAV_CNS.

CONCLUSIONS

Significant CO drops produce increased predicted plasma concentrations corresponding to deeper anesthesia, which is potentially dangerous for elderly patients. PBPK-PD model simulations allow studying and quantifying these effects to improve clinical practice.

Hypoalbuminemia-Related Prolonged Sedation After General Anesthesia: A Case Report

A 69-year-old man underwent total laryngopharyngectomy with radial forearm free flap reconstruction. He had lost 15 kg over a period of 6 months and did not receive any preoperative nutritional workup or management. The patient had a general total intravenous anesthetic with ketamine, lidocaine, and propofol, which was uneventful for an 8-hour surgery. The patient remained deeply sedated for 4 hours after discontinuation of all sedative medications. Diagnostic workup only revealed hypoalbuminemia and hypoproteinemia. We hypothesized relative overdosage of sedative anesthetic drugs due to preoperative malnutrition accentuated by intraoperative fluid administration.

Volatile Anesthesia Versus Total Intravenous Anesthesia During Cardiopulmonary Bypass: A Narrative Review on the Technical Challenges and Considerations

The Mortality in Cardiac Surgery Randomized Controlled Trial of Volatile Anesthetics (MYRIAD) demonstrated that cardiac surgery with either volatile anesthesia or intravenous anesthesia techniques can be comparable with respect to morbidity and mortality. Maintaining anesthesia during cardiopulmonary bypass (CPB) with either approach requires appreciation of the nuances that are unique to each. This narrative review addresses these technical challenges and other considerations.

The Molecular Mechanisms Associated with the Effects of Propofol in a Rat Model of Pain Due to Inflammation Following Injection with Complete Freund's Adjuvant

Background

This study aimed to investigate the molecular mechanisms associated with the effects of propofol in a rat model of pain due to inflammation following subcutaneous injection with complete Freund’s adjuvant (CFA).

Material/Methods

Sprague-Dawley rats were injected subcutaneously in the paw with CFA. Propofol or saline was administered by tail vein injection. After CFA treatment for 0 hours, 4 hours, 1 day, 4 days, 7 days, and 14 days, the behavior of the rats was assessed. An enzyme-linked immunosorbent assay (ELISA) measured serum levels of proinflammatory cytokines, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. Western blot and the quantitative reverse-transcription polymerase chain reaction (qRT-PCR) were used to detect levels of p38MAPK and NF-κB related mRNA and proteins, including p-p38, p38, p65, p-p65, NOD-like receptor family protein 3 (NLRP3), apoptosis-associated speck-like protein (ASC) and caspase-1 in rat spinal cord tissues.

Results

Injection of CFA significantly reduced the mechanical withdrawal threshold (MWT), thermal withdrawal latency (TWL), and frequency responses to cold stimulation. Propofol treatment significantly reduced serum levels of TNF-α, IL-1β, and IL-6. Protein expression levels of p-p38 and p-p65 were upregulated in the rat model, which were inhibited by propofol treatment. CFA injection increased the expression levels of NLRP3, ASC, and caspase-1 in the spinal cord tissues of rats, which were reduced by propofol treatment.

Conclusions

In a rat model of pain following subcutanous injection with CFA, propofol reduced CFA-induced pain and inhibited the inflammatory response through the p38MAPK-nuclear factor-κB (NF-κB) pathway and the NLRP3 inflammasome.

A sensitive liquid chromatography method for analysis of propofol in small volumes of neonatal blood

WHAT IS KNOWN AND OBJECTIVE

Sampling volumes of blood from neonates is necessarily limited. However, most of the published propofol analysis assays require a relatively large blood sample volume (typically ≥0.5 mL). Therefore, the aim of the present study was to develop and validate a sensitive method requiring a smaller sample volume (0.2 mL) to fulfill clinically relevant research requirements.

METHODS

Following simple protein precipitation and centrifugation, the supernatant was injected into the HPLC-fluorescence system and separated with a reverse phase column. Propofol and the internal standard (thymol) were detected and quantified using fluorescence at excitation and emission wavelengths of 270 nm and 310 nm, respectively. The method was validated with reference to the Food and Drug Administration (FDA) guidance for industry. Accuracy (CV, %) and precision (RSD, %) were evaluated at three quality control concentration levels (0.05, 0.5 and 5 µg/mL).

RESULTS AND DISCUSSION

Calibration curves were linear in the range of 0.005-20 µg/mL. Intra- and interday accuracy (-4.4%-13.6%) and precision (0.2%-5.8%) for propofol were below 15%. The calculated LOD (limit of detection) and LLOQ (lower limit of quantification) were 0.0021 µg/mL and 0.0069 µg/mL, respectively. Propofol samples were stable for 4 months at -20°C after the sample preparation. This method was applied for analyzing blood samples from 41 neonates that received propofol, as part of a dose-finding study. The measured median (range) concentration was 0.14 (0.03-1.11) µg/mL, which was in the range of the calibration curve. The calculated median (range) propofol half-life of the gamma elimination phase was 10.4 (4.7-26.7) hours.

WHAT IS NEW AND CONCLUSION

A minimal volume (0.2 mL) of blood from neonates is required for the determination of propofol with this method. The method can be used to support the quantification of propofol drug concentrations for pharmacokinetic studies in the neonatal population.

Propofol Attenuates the Myocardial Protection Properties of Desflurane by Modulating Mitochondrial Permeability Transition

BACKGROUND

Desflurane and propofol are cardioprotective, but relative efficacy is unclear. The aim was to compare myocardial protection of single, simultaneous, and serial administration of desflurane and propofol.

METHODS

Sixty New Zealand White rabbits and 65 isolated Sprague Dawley rat hearts randomly received desflurane, propofol, simultaneous desflurane and propofol, or sequential desflurane then propofol. Rabbits were subdivided to receive either ischemia-reperfusion with temporary occlusion of the left anterior descending artery or a time-matched, nonischemic perfusion protocol, whereas rat hearts were perfused in a Langendorff model with global ischemia-reperfusion. End points were hemodynamic, functional recovery, and mitochondrial uptake of H-2-deoxy-D-glucose as an indicator of mitochondrial permeability transition.

RESULTS

In rabbits, there were minimal increases in preload-recruitable stroke-work with propofol (P < .001), desflurane (P < .001), and desflurane-and-propofol (P < .001) groups, but no evidence of increases with pentobarbitone (P = .576) and desflurane-then-propofol (P = .374). In terms of end-diastolic pressure-volume relationship, there was no evidence of increase compared to nonischemic controls with desflurane-then-propofol (P = .364), a small but significant increase with desflurane (P < .001), and larger increases with pentobarbitone (P < .001), propofol (P < .001), and desflurane-and-propofol (P < .001).In rat hearts, there was no statistically significant difference in mitochondrial H-activity between propofol and desflurane-and-propofol (165 ± 51 × 10 vs 154 ± 51 × 10 g·mL·min/μmol; P = .998). Desflurane had lower uptake than propofol (65 ± 21 × 10 vs 165 ± 51 × 10 g·mL·min/μmol; P = .039), but there was no statistically significant difference between desflurane and desflurane-then-propofol (65 ± 21 × 10 vs 59 ± 11 × 10 g·mL·min/μmol; P = .999).

CONCLUSIONS

Propofol and desflurane are cardioprotective, but desflurane is more effective than propofol. The added benefit of desflurane is lost when used simultaneously with propofol.

Evaluating Propofol Concentration in Blood From Exhaled Gas Using a Breathing-Related Partition Coefficient

BACKGROUND

The anesthetic side effects of propofol still occur in clinical practice because no reliable monitoring techniques are available. In this regard, continuous monitoring of propofol in breath is a promising method, yet it remains infeasible because there is large variation in the blood/exhaled gas partial pressure ratio (RBE) in humans. Further evaluations of the influences of breathing-related factors on RBE would mitigate this variation.

METHODS

Correlations were analyzed between breathing-related factors (tidal volume [TV], breath frequency [BF], and minute ventilation [VM]) and RBE in 46 patients. Furthermore, a subset of 10 patients underwent pulmonary function tests (PFTs), and the parameters of the PFTs were then compared with the RBE. We employed a 1-phase exponential decay model to characterize the influence of VM on RBE. We also proposed a modified RBE (RBEM) that was not affected by the different breathing patterns of the patients. The blood concentration of propofol was predicted from breath monitoring using RBEM and RBE.

RESULTS

We found a significant negative correlation (R = -0.572; P < .001) between VM and RBE (N = 46). No significant correlation was shown between PFTs and RBE in the subset (N = 10). RBEM demonstrated a standard Gaussian distribution (mean, 1.000; standard deviation [SD], 0.308). Moreover, the predicted propofol concentrations based on breath monitoring matched well with the measured blood concentrations. The 90% prediction band was limited to within ±1 μg·mL.

CONCLUSIONS

The prediction of propofol concentration in blood was more accurate using RBEM than when using RBE and could provide reference information for anesthesiologists. Moreover, the present study provided a general approach for assessing the influence of relevant physiological factors and will inform noninvasive and accurate breath assessment of volatile drugs or metabolites in blood.

Effect of incubation with crystalloid solutions or medications on packed red blood cells

BACKGROUND

American Association of Blood Banks (AABB) guidelines suggest that packed red blood cells (PRBCs) be administered through a dedicated intravenous (IV) catheter. Literature supporting this broad-scope declaration are scarce. Obtaining additional IV access is painful, costly, and an infectious risk. We evaluated the effect of co-incubating PRBCs with crystalloids and medications on PRBC hemolysis, membrane deformability, and aggregation, as well as medication concentration.

METHODS

PRBCs were co-incubated 5 minutes with plasma, normal saline (NS), 5% dextrose in water (D5W), Plasmalyte, epinephrine (epi), norepinephrine (norepi), dopamine (dopa), or Propofol (prop). Samples were then assessed for hemolysis (free hemoglobin, serum potassium), membrane deformability (elongation index [EI]), aggregation (smear, critical shear stress [mPa]) and drug concentration (High Performance Liquid Chromatography/Tandem Mass Spectrometry [LCMS-MS]). Significance (p ≤ 0.05) was determined by Wilcoxon-paired comparisons or Wilcoxon/Kruskall Willis with post-hoc Dunn's test.

RESULTS

Compared to co-incubation with plasma: 1) co-incubation resulted in significantly increased hemolysis only when D5W as used (free hemoglobin, increased potassium); 2) EI trended lower when co-incubated with D5W and trended toward higher when co-incubated with prop; 3) aggregation was significantly lower when PRBCs co-incubated with NS, D5W, or Plasmalyte, and trended lower when co-incubated with epi, norepi, or dopa. Medication concentrations were between those predicted by distribution only in plasma and distribution through the entire intra- and extracellular space.

CONCLUSION

Our data suggest that 5 minutes of PRBC incubation with isotonic crystalloids or catecholamines does not deleteriously alter PRBC hemolysis, membrane deformability, or aggregation. Co-incubation with D5W likely increases hemolysis. Propofol may promote hemolysis.

Clinical Pharmacokinetics and Pharmacodynamics of Propofol

Propofol is an intravenous hypnotic drug that is used for induction and maintenance of sedation and general anaesthesia. It exerts its effects through potentiation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) at the GABAA receptor, and has gained widespread use due to its favourable drug effect profile. The main adverse effects are disturbances in cardiopulmonary physiology. Due to its narrow therapeutic margin, propofol should only be administered by practitioners trained and experienced in providing general anaesthesia. Many pharmacokinetic (PK) and pharmacodynamic (PD) models for propofol exist. Some are used to inform drug dosing guidelines, and some are also implemented in so-called target-controlled infusion devices, to calculate the infusion rates required for user-defined target plasma or effect-site concentrations. Most of the models were designed for use in a specific and well-defined patient category. However, models applicable in a more general population have recently been developed and published. The most recent example is the general purpose propofol model developed by Eleveld and colleagues. Retrospective predictive performance evaluations show that this model performs as well as, or even better than, PK models developed for specific populations, such as adults, children or the obese; however, prospective evaluation of the model is still required. Propofol undergoes extensive PK and PD interactions with both other hypnotic drugs and opioids. PD interactions are the most clinically significant, and, with other hypnotics, tend to be additive, whereas interactions with opioids tend to be highly synergistic. Response surface modelling provides a tool to gain understanding and explore these complex interactions. Visual displays illustrating the effect of these interactions in real time can aid clinicians in optimal drug dosing while minimizing adverse effects. In this review, we provide an overview of the PK and PD of propofol in order to refresh readers' knowledge of its clinical applications, while discussing the main avenues of research where significant recent advances have been made.

LC-MS for Simultaneous Determination of Vancomycin and Teicoplanin in Patient Plasma and its Application to Therapeutic Drug Monitoring

Background:

Therapeutic drug monitoring is recommended for patients taking vancomycin and teicoplanin to ensure pharmaceutical efficacy and prevent toxicity. Only few studies were reported regarding the simultaneous determination of vancomycin and teicoplanin in human plasma.

Objective:

The study aimed at developing and validating a Liquid Chromatography-Mass Spectrometry (LC-MS) method for simultaneous determination and therapeutic drug monitoring of vancomycin and teicoplanin in patients with severe infection.

Method:

Plasma was processed by protein precipitation extraction. The analytes were separated on a C18 column by gradient elution with 0.1% formic acid and acetonitrile as mobile phase and measured by electrospray ionization source in positive selective ion monitoring mode at m/z 724.7 (vancomycin), 940.7 (teicoplanin) and 329.0 (bergenin). The plasma samples (104) were obtained from patients who were taking vancomycin or teicoplanin for further analysis.

Results:

The calibration curves were linear within the range of 0.25–40 µg/mL for vancomycin, and 0.5-40 µg/mL for teicoplanin. Either inter- or intra-day precision was less than 10.01 %. The extraction recoveries ranged from 89.99 to 94.29% for vancomycin and from 39.83 to 40.16 % for teicoplanin. Vancomycin and teicoplanin in plasma were stable at various storage conditions. The measured mean trough concentrations were 12.313 µg/mL for vancomycin and 8.765 µg/mL for teicoplanin.

Conclusion:

This method was successfully applied to therapeutic drug monitoring of vancomycin and teicoplanin in patients. It is with great clinic value for monitoring and predicting the individual response of patients under treatment.

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.

In vitro changes in the proportion of protein-unbound-free propofol induced by valproate

PURPOSE

It has been reported that oral valproate (VPA) reduces the dose of propofol required for sedation. As  a potential reason for this, it is considered that VPA displaces serum protein-bound propofol and increases the proportion of protein-unbound-free propofol. To examine this hypothesis, the present in vitro study investigated the influence of VPA on the proportion of protein-unbound-free propofol in human serum samples.

METHODS

Serum samples were collected from 10 healthy volunteers, who were not taking any medication. VPA (final concentration: 0.05, 0.1 or 1 mg/mL) and propofol (final concentration: 1 or 5 µg/mL) were mixed with serum samples with normal (4.0 g/dL) or low (2.5 g/dL) albumin concentrations. Then, protein-unbound-free propofol was extracted from the samples, and its concentration was measured using high-performance liquid chromatography. We compared the proportion of protein-unbound-free propofol in each of the VPA-containing samples with that in serum samples without VPA (control).

RESULTS

In the serum samples with normal albumin concentrations, 1 mg/mL VPA significantly increased the proportion of protein-unbound-free propofol at 1 and 5 µg/mL propofol. Furthermore, in the serum samples with low albumin concentrations, the proportion of protein-unbound-free propofol was significantly increased by both 0.1 and 1 mg/mL VPA at propofol concentrations of 1 and 5 µg/mL.

CONCLUSION

VPA might increase the proportion of protein-unbound-free propofol in human serum via displacement reactions.

Physiologically Based Pharmacokinetic Modeling of Renally Cleared Drugs in Pregnant Women

BACKGROUND

Since pregnant women are considerably underrepresented in clinical trials, information on optimal dosing in pregnancy is widely lacking. Physiologically based pharmacokinetic (PBPK) modeling may provide a method for predicting pharmacokinetic changes in pregnancy to guide subsequent in vivo pharmacokinetic trials in pregnant women, minimizing associated risks.

OBJECTIVES

The goal of this study was to build and verify a population PBPK model that predicts the maternal pharmacokinetics of three predominantly renally cleared drugs (namely cefazolin, cefuroxime, and cefradine) at different stages of pregnancy. It was further evaluated whether the fraction unbound (f _u) could be estimated in pregnant women using a proposed scaling approach.

METHODS

Based on a recent literature review on anatomical and physiological changes during pregnancy, a pregnancy population PBPK model was built using the software PK-Sim^®/MoBi^®. This model comprised 27 compartments, including nine pregnancy-specific compartments. The PBPK model was verified by comparing the predicted maternal pharmacokinetics of cefazolin, cefuroxime, and cefradine with observed in vivo data taken from the literature. The proposed scaling approach for estimating the f _u in pregnancy was evaluated by comparing the predicted f _u with experimentally observed f _u values of 32 drugs taken from the literature.

RESULTS

The pregnancy population PBPK model successfully predicted the pharmacokinetics of cefazolin, cefuroxime, and cefradine at all tested stages of pregnancy. All predicted plasma concentrations fell within a 2-fold error range and 85% of the predicted concentrations within a 1.25-fold error range. The f _u in pregnancy could be adequately predicted using the proposed scaling approach, although a slight underestimation was evident in case of drugs bound to α₁-acidic glycoprotein.

CONCLUSION

Pregnancy population PBPK models can provide a valuable tool to predict a priori the pharmacokinetics of predominantly renally cleared drugs in pregnant women. These models can ultimately support informed decision making regarding optimal dosing regimens in this vulnerable special population.

Effect of Propofol on breast Cancer cell, the immune system, and patient outcome

Breast cancer is the second leading cause of cancer death in women. Surgery is the first line of treatment for breast cancer. Retrospective clinical studies suggest that the type of anesthesia administered during oncological surgery may influence patient outcome. Propofol, the widely used intravenous anesthetic agent, may lead to better outcomes compared to volatile anesthetics. Here we review the literature on the effect of propofol in breast cancer cells, the immune system, pain management, and patient outcomes. Evidence from the study of breast cancer cell lines suggests that high concentrations of propofol have both anti-tumor and pro-tumor effects. Propofol and volatile anesthetics have different effects on the immune system. Propofol has also been shown to reduce the development and severity of acute and chronic pain following surgery. Although a retrospective study that included many types of cancer indicated that propofol increases the long-term survival of patients following surgery, the evidence for this in breast cancer is weak. It has been shown that Propofol combined with paravertebral block led to change of serum composition that affects the breast cancer cell behaviors and natural killer cell activity. Prospective studies are in progress and will be finished within 5 years. The existing evidence is not sufficient to warrant changes to current anesthetic management. Further research is needed to clarify the mechanisms by which propofol affects cancer cells and the immune system.

Metabolic Profiles of Propofol and Fospropofol: Clinical and Forensic Interpretative Aspects

Propofol is an intravenous short-acting anesthetic widely used to induce and maintain general anesthesia and to provide procedural sedation. The potential for propofol dependency and abuse has been recognized, and several cases of accidental overdose and suicide have emerged, mostly among the health professionals. Different studies have demonstrated an unpredictable interindividual variability of propofol pharmacokinetics and pharmacodynamics with forensic and clinical adverse relevant outcomes (e.g., pronounced respiratory and cardiac depression), namely, due to polymorphisms in the UDP-glucuronosyltransferase and cytochrome P450 isoforms and drugs administered concurrently. In this work the pharmacokinetics of propofol and fospropofol with particular focus on metabolic pathways is fully reviewed. It is concluded that knowing the metabolism of propofol may lead to the development of new clues to help further toxicological and clinical interpretations and to reduce serious adverse reactions such as respiratory failure, metabolic acidosis, rhabdomyolysis, cardiac bradyarrhythmias, hypotension and myocardial failure, anaphylaxis, hypertriglyceridemia, renal failure, hepatomegaly, hepatic steatosis, acute pancreatitis, abuse, and death. Particularly, further studies aiming to characterize polymorphic enzymes involved in the metabolic pathway, the development of additional routine forensic toxicological analysis, and the relatively new field of ‘‘omics” technology, namely, metabolomics, can offer more in explaining the unpredictable interindividual variability.

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.

Thalamocortical control of propofol phase-amplitude coupling

The anesthetic propofol elicits many different spectral properties on the EEG, including alpha oscillations (8-12 Hz), Slow Wave Oscillations (SWO, 0.1-1.5 Hz), and dose-dependent phase-amplitude coupling (PAC) between alpha and SWO. Propofol is known to increase GABAA inhibition and decrease H-current strength, but how it generates these rhythms and their interactions is still unknown. To investigate both generation of the alpha rhythm and its PAC to SWO, we simulate a Hodgkin-Huxley network model of a hyperpolarized thalamus and corticothalamic inputs. We find, for the first time, that the model thalamic network is capable of independently generating the sustained alpha seen in propofol, which may then be relayed to cortex and expressed on the EEG. This dose-dependent sustained alpha critically relies on propofol GABAA potentiation to alter the intrinsic spindling mechanisms of the thalamus. Furthermore, the H-current conductance and background excitation of these thalamic cells must be within specific ranges to exhibit any intrinsic oscillations, including sustained alpha. We also find that, under corticothalamic SWO UP and DOWN states, thalamocortical output can exhibit maximum alpha power at either the peak or trough of this SWO; this implies the thalamus may be the source of propofol-induced PAC. Hyperpolarization level is the main determinant of whether the thalamus exhibits trough-max PAC, which is associated with lower propofol dose, or peak-max PAC, associated with higher dose. These findings suggest: the thalamus generates a novel rhythm under GABAA potentiation such as under propofol, its hyperpolarization may determine whether a patient experiences trough-max or peak-max PAC, and the thalamus is a critical component of propofol-induced cortical spectral phenomena. Changes to the thalamus may be a critical part of how propofol accomplishes its effects, including unconsciousness.

Non-oncotic properties of albumin. A multidisciplinary vision about the implications for critically ill patients

INTRODUCTION

Effective resuscitation with human albumin solutions is achieved with less fluid than with crystalloid solutions. However, the role of albumin in today's critical care unit is also linked to its multiple pharmacological effects. Areas covered: The potential clinical benefits of albumin in select populations of critically ill patients like sepsis seem related to immunomodulatory and anti-inflammatory effects, antibiotic transportation and endothelial stabilization. Albumin transports many drugs used in critically ill patients. Such binding to albumin is frequently lessened in critically ill patients with hypoalbuminemia. These changes could result in sub-optimal treatment. Albumin has immunomodulatory capacity by binding several bacterial products. Albumin also influences vascular integrity, contributing to the maintenance of the normal capillary permeability. Moreover, the albumin molecule encompasses several antioxidant properties, thereby significantly reducing re-oxygenation injury, which is especially important in sepsis. In fact, most studies of albumin administration are a combination of a degree of resuscitation with a degree of maintenance or supplementation of albumin. Expert commentary: The potential clinical benefits of the use of albumin in selected critically ill patients such as sepsis seem related to its immunomodulatory and anti-inflammatory effects, antioxidant properties, antibiotic transportation and endothelial stabilization. Additional studies are warranted to further elucidate the underlying physiologic and molecular rationale.

In silico investigation of propofol binding sites in human serum albumin using explicit and implicit solvation models

All-atom molecular dynamics (MD) simulations are presented on general anesthetic propofol bound to human serum albumin (HSA) due to the drug pharmacokinetics and pharmacodynamics in the circulatory system. We implemented the explicit and implicit solvation models to compare the binding affinity of propofol at the different binding sites (PR1 and PR2) in the HSA protein. Only the implicit solvation models provided the evidence in accordance with the experimental data indicating that the HSA-ligand interactions are dominanted by hydrophobic forces due to the higher drug affinity at the PR1 position with a ΔG_MM-PB/SA value of -23.44kcalmol^-1. Overall, this study provides important information on the accuracy of explicit and implicit solvation models to characterize the propofol interaction with different HSA binding sites.

The influence of storage time and temperature on propofol concentrations in canine blood and plasma

Propofol is an intravenous anesthetic commonly used due to its favorable pharmacokinetic and pharmacodynamic profile. There are discrepancies in the literature about the most appropriate sample for determining propofol concentrations. Although plasma has been used for determining propofol concentrations, whole blood has been the preferred sample. There is also a lack of consistency in the literature on the effect of storage time and temperature on propofol concentrations and this may lead to errors in the design of pharmacokinetic/pharmacodynamics studies. The purpose of this study was to determine the difference in propofol concentrations in whole blood versus plasma and to evaluate the influence of storage time (56 days) and temperature (4 °C, −20 °C, −80 °C) on the stability of propofol concentrations in blood and plasma samples. Results from the study indicate that whole blood and plasma samples containing propofol stored at −80 °C have concentrations as high as or higher than those stored at 4 °C or −20 °C for 56 days; thus, −80 °C is an appropriate temperature for propofol sample storage. Plasma propofol concentrations were consistently higher than whole blood for all three storage temperatures. Consequently, plasma is the most appropriate sample for propofol analysis due to its consistent determinations.

Significant decreases in blood propofol concentrations during adrenalectomy for phaeochromocytoma

AIM

The kinetics of propofol are influenced by cardiac output. The aim of this study was to examine changes in blood propofol concentrations during phaeochromocytoma surgery using target-controlled infusion (TCI) anaesthesia with propofol.

METHODS

This is a prospective observational study. Ten patients with phaeochromocytoma who underwent unilateral adrenalectomy were included. Cardiac output was measured using an arterial pressure-based cardiac output analysis method. The target blood propofol concentrations were adjusted to maintain an approximate bispectral index (BIS) value of 40 before initiating surgery. The settings remained constant during surgery. Blood samples for propofol concentrations were collected from the radial artery at seven time points: two before tumour manipulation (T1, 2), two during tumour manipulation (T3, 4), and three after tumour vein ligation (T4-7). BIS values, the arterial pressure cardiac index (APCI) and haemodynamic parameters were measured at the same time points as the blood samples. The prop-ratio was calculated by dividing blood propofol concentrations by target concentrations of TCI.

RESULTS

APCI increased during tumour manipulation and after tumour vein ligation. The prop-ratio was reduced significantly by approximately 40% and showed a significant negative correlation with APCI. BIS values increased significantly and showed a significant negative correlation with the prop-ratio.

CONCLUSION

The increased APCI during tumour manipulation and after tumour vein ligation was associated with markedly reduced blood propofol concentrations. These results reveal that significant decreases in the anaesthetic effect may be observed in patients undergoing phaeochromocytoma surgery even if TCI anaesthesia is used with propofol.

Propofol-induced mitochondrial and contractile dysfunction of the rat ventricular myocardium

Propofol is a short-acting hypnotic agent used in human medicine for sedation and general anesthesia. Its administration can be associated with serious cardiovascular side-effects that include decrease in arterial blood pressure and cardiac output. The aim of the present study was to evaluate propofol effects on mitochondrial respiration, myocardial contractility and electrophysiology in the same samples isolated from the heart ventricles of adult rats. Mitochondrial oxygen consumption was measured in permeabilized samples dissected from free walls of both ventricles using high-resolution respirometry. State LEAK was determined with malate and glutamate. Active respiration was induced by ADP (state PI) and further by succinate, a Complex II substrate (PI+II). Rotenone was injected to measure state PII. Antimycin A, a Complex III inhibitor was used to determine residual oxygen consumption (ROX). N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride and ascorbate were injected simultaneously for respirometric assay of cytochrome c oxidase activity (CIV). Isometric contractions and membrane potentials were determined on multicellular preparations isolated from right and left ventricles. Propofol concentrations used ranged from 0.005 to 0.5 mmol/l. All respiratory parameters were significantly higher in the left control ventricles compared to the right ones. Propofol significantly decreased Complex I activity at concentration 0.025 mmol/l and papillary muscle contraction force at 0.1 mmol/l. Propofol did not affect action potential duration at any concentration studied. Our study suggests that mechanisms contributing to the impaired myocardial contraction during propofol anesthesia might include also mitochondrial dysfunction manifested by compromised activity of the respiratory Complex I.

Determination of binding properties of ampicillin in drug-human serum albumin standard solution using N-vinylpyrrolidone copolymer combined with the micellar systems

It is well-known that only the unbound (free) drug fraction can achieve a pharmacological effect. Therefore the determination of free drug concentration is a very important issue in the field of pharmacology. In this study poly-1-vinyl-2-pyrrolidone (VP) crosslinked with divinylbenzene (DVB) compared with the micellar liquid chromatography (MLC) with and without pre-made drug adsorption was used for quantitative analysis of free ampicillin concentration in the standard solution of drug-human serum albumin owing to its ability to block protein adsorption. The commonly recognized adsorption method based on drug adsorption on VP-DVB has been compared to the entirely new application of MLC with direct sample injection (DSI) not requiring pre-made adsorption. Micellar aggregates are able to solubilize various compounds therefore micellar environment can be used for direct determination of free drug concentration. The obtained results show that the free drug concentration values obtained in the micellar systems based on cetyltrimethylammonium bromide (CTAB) (93.98μgL^-1, 78.3%) as well as on polyoxyethylene (23) lauryl ether (Brij35) (91.15μgL^-1, 75.9%) are similar to those obtained after the drug adsorption on VP-DVB using both RP-HPLC (95.85μgmL^-1, 79.9%) and spectrophotometry (96.47μgmL^-1, 80.4%). However, only %PPB (% plasma protein binding) value calculated on the basis of Brij35 retention factor is similar to the literature data. The obtained results are within the analytical range of % of free drug concentration. Therefore N-vinylpyrrolidone copolymer as well as micellar system based on the non-ionic surfactant can be successfully applied for determination of free drug concentration. Moreover, the new application of MLC with DSI can be recognized as a promising, fast and simple method for quantitative determination of free drug concentration.

Propofol Enhances Hemoglobin-Induced Cytotoxicity in Neurons

BACKGROUND

It has been increasingly suggested that propofol protects against hypoxic-/ischemic-induced neuronal injury. As evidenced by hemorrhage-induced stroke, hemorrhage into the brain may also cause brain damage. Whether propofol protects against hemorrhage-induced brain damage remains unknown. Therefore, in this study, we investigated the effects of propofol on hemoglobin-induced cytotoxicity in cultured mouse cortical neurons.

METHODS

Neurons were prepared from the cortex of embryonic 15-day-old mice. Hemoglobin was used to induce cytotoxicity in the neurons. The neurons were then treated with propofol for 4 hours. Cytotoxicity was determined by lactate dehydrogenase release assay. Caspase-3 activation was examined by Western blot analysis. Finally, the free radical scavenger U83836E was used to examine the potential involvement of oxidative stress in propofol's effects on hemoglobin-induced cytotoxicity.

RESULTS

We found that treatment with hemoglobin induced cytotoxicity in the neurons. Propofol enhanced hemoglobin-induced cytotoxicity. Specifically, there was a significant difference in the amount of lactate dehydrogenase release between hemoglobin plus saline (19.84% ± 5.38%) and hemoglobin plus propofol (35.79% ± 4.41%) in mouse cortical neurons (P = 0.00058, Wilcoxon Mann-Whitney U test, n = 8 in the control group or the treatment group). U83836E did not attenuate the enhancing effects of propofol on hemoglobin-induced cytotoxicity in the neurons, and propofol did not significantly affect caspase-3 activation induced by hemoglobin. These data suggested that caspase-3 activation and oxidative stress might not be the underlying mechanisms by which propofol enhanced hemoglobin-induced cytotoxicity. Moreover, these data suggested that the neuroprotective effects of propofol would be dependent on the condition of the brain injury, which will need to be confirmed in future studies.

CONCLUSIONS

These results from our current proof-of-concept study should promote more research in vitro and in vivo to develop better anesthesia care for patients with hemorrhagic stroke.

Determination of total and unbound propofol in patients during intensive care sedation by ultrafiltration and LC-MS/MS

For the quantification of propofol total and unbound drug concentrations a sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated. To separate unbound propofol an ultrafiltration step before sample preparation was performed. Both the ultrafiltrate and plasma samples were extracted with solid-phase extraction and substituted with deuterated propofol as an internal standard. Separation was performed by gradient elution using UPLC-like system and analyzed by MS/MS consisting of an electrospray ionization source. To detect low and high concentration levels of propofol two calibration curves were identified and showed linearity within the range of 1-50ng/ml and 50-20000ng/ml. The lower limit of quantification was 1ng/ml. Intra- and interassay precision and accuracy did not exceed ±15%. The method was applied to a clinical study during intensive care treatment of patients after coronary artery bypass grafting.

Propofol Pharmacokinetics and Estimation of Fetal Propofol Exposure during Mid-Gestational Fetal Surgery: A Maternal-Fetal Sheep Model

BACKGROUND

Measuring fetal drug concentrations is extremely difficult in humans. We conducted a study in pregnant sheep to simultaneously describe maternal and fetal concentrations of propofol, a common intravenous anesthetic agent used in humans. Compared to inhalational anesthesia, propofol supplemented anesthesia lowered the dose of desflurane required to provide adequate uterine relaxation during open fetal surgery. This resulted in better intraoperative fetal cardiac outcome. This study describes maternal and fetal propofol pharmacokinetics (PK) using a chronically instrumented maternal-fetal sheep model.

METHODS

Fetal and maternal blood samples were simultaneously collected from eight mid-gestational pregnant ewes during general anesthesia with propofol, remifentanil and desflurane. Nonlinear mixed-effects modeling was performed by using NONMEM software. Total body weight, gestational age and hemodynamic parameters were tested in the covariate analysis. The final model was validated by bootstrapping and visual predictive check.

RESULTS

A total of 160 propofol samples were collected. A 2-compartment maternal PK model with a third fetal compartment appropriately described the data. Mean population parameter estimates for maternal propofol clearance and central volume of distribution were 4.17 L/min and 37.7 L, respectively, in a typical ewe with a median heart rate of 135 beats/min. Increase in maternal heart rate significantly correlated with increase in propofol clearance. The estimated population maternal-fetal inter-compartment clearance was 0.0138 L/min and the volume of distribution of propofol in the fetus was 0.144 L. Fetal propofol clearance was found to be almost negligible compared to maternal clearance and could not be robustly estimated.

CONCLUSIONS

For the first time, a maternal-fetal PK model of propofol in pregnant ewes was successfully developed. This study narrows the gap in our knowledge in maternal-fetal PK model in human. Our study confirms that maternal heart rate has an important influence on the pharmacokinetics of propofol during pregnancy. Much lower propofol concentration in the fetus compared to maternal concentrations explain limited placental transfer in in-vivo paired model, and less direct fetal cardiac depression we observed earlier with propofol supplemented inhalational anesthesia compared to higher dose inhalational anesthesia in humans and sheep.

Evidence of Different Propofol Pharmacokinetics under Short and Prolonged Infusion Times in Rabbits

Propofol is an anaesthetic widely used in both human beings and animals. However, the characterization of propofol pharmacokinetics (PK) is not well understood when long-term infusions are used. The main objective of this study was to explore the PK behaviour of propofol in a rabbit model during short and prolonged propofol infusions and to develop an internally validated PK model, for propofol dose individualization in the rabbit for future use. Population 1 (P1) was constituted by seven New Zealand rabbits and was used to characterize the PK profile of propofol at short infusions. Animals were anaesthetized with a bolus of 20 mg/kg, followed by an infusion rate of 50 mg/kg/hr of propofol at 1%, which was then maintained for 30 min. A second rabbit population (P2, n = 7) was sedated according to reflexes responses and Index of Consciousness values, for 20 consecutive hours using propofol 2% aiming at characterizing propofol behaviour at long-term infusions. Clinical data and blood samples were collected at specific time-points in both populations. Propofol plasma concentrations were determined by gas chromatography/ion trap mass spectrometry. The NONMEM VII software was used to evaluate the relationships between dose and plasma concentrations. A linear two-compartment model with different central compartment volume and plasma clearance (separately modelled in the two populations) was the one that best described propofol concentrations. The time course of propofol plasma concentrations was well characterized by the PK model developed, which simultaneously accounts for propofol short- and long-term infusions and can be used to optimize future PK studies in rabbits.

Propofol detection and quantification in human blood: the promise of feedback controlled, closed-loop anesthesia

The performance of a membrane-coated voltammetric sensor for propofol (2,6-diisopropylphenol) has been characterized in long term monitoring experiments using an automated flow analytical system (AFAS) and by analyzing human serum and whole blood samples by standard addition. It is shown that the signal of the membrane-coated electrochemical sensor for propofol is not influenced by the components of the pharmaceutical formulation of propofol (propofol injectable emulsion). The current values recorded with the electrochemical propofol sensor in buffer solutions and human serum samples spiked with propofol injectable emulsion showed excellent correlation with the peak heights recorded with an UV-Vis detector during the HPLC analysis of these samples (R(2) = 0.997 in PBS and R(2) = 0.975 in human serum). However, the determination of propofol using the electrochemical method is simpler, faster and has a better detection limit (0.08 ± 0.05 μM) than the HPLC method (0.4 ± 0.2 μM). As a first step towards feedback controlled closed-loop anesthesia, the membrane-coated electrochemical sensor has been implemented onto surface of an intravenous catheter. The response characteristics of the membrane-coated carbon fiber electrode on the catheter surface were very similar to those seen using a macroelectrode.