A simple method for detecting plasma propofol

Propofol misuse in Ireland - Two case reports and a review of the literature

Propofol is a rapidly acting sedative drug, which is usually administered intravenously. It is widely used in procedural sedation due to its rapid onset and easy reversibility. It has a good safety profile when used in combination with ventilation and monitoring. However, propofol can bring on feelings of euphoria, sexual disinhibition, tension relief and hallucinations, creating a potential for abuse. At an international level, recreational propofol use among medical staff is a growing, yet under reported problem. In order to highlight this issue in an Irish context, the case reports described are among the first recorded deaths in Ireland due to unmonitored self-administration of propofol. The difficulties facing forensic pathologists in detecting propofol and its metabolites in these cases are outlined. The potential for propofol abuse should influence healthcare facilities to make their staff aware of the risks associated with it. This in turn would promote vigilance and encourage those affected to seek treatment.

Gas chromatograph-surface acoustic wave for quick real-time assessment of blood/exhaled gas ratio of propofol in humans

BACKGROUND

Although pilot studies have reported that exhaled propofol concentrations can reflect intraoperative plasma propofol concentrations in an individual, the blood/exhaled partial pressure ratio RBE varies between patients, and the relevant factors have not yet been clearly addressed. No efficient method has been reported for the quick evaluation of RBE and its association with inter-individual variables.

METHODS

We proposed a novel method that uses a surface acoustic wave (SAW) sensor combined with a fast gas chromatograph (GC) to simultaneously detect propofol concentrations in blood and exhaled gas in 28 patients who were receiving propofol i.v. A two-compartment pharmacokinetic (PK) model was established to simulate propofol concentrations in exhaled gas and blood after a bolus injection. Simulated propofol concentrations for exhaled gas and blood were used in a linear regression model to evaluate RBE.

RESULTS

The fast GC-SAW system showed reliability and efficiency for simultaneous quantitative determination of propofol in blood (correlation coefficient R(2)=0.994, P<0.01) and exhaled gas (R(2)=0.991, P<0.01). The evaluation of RBE takes <50 min for a patient. The distribution of RBE in 28 patients showed inter-individual differences in RBE (median 1.27; inter-quartile range 1.07-1.59).

CONCLUSIONS

Fast GC-SAW, which analyses samples in seconds, can perform both rapid monitoring of exhaled propofol concentrations and fast analysis of blood propofol concentrations. The proposed method allows early determination of the coefficient RBE in individuals. Further studies are required to quantify the distribution of RBE in a larger cohort and assess the effect of other potential factors.

CLINICAL TRIAL REGISTRATION

ChiCTR-ONC-13003291.

Caveolae and propofol effects on airway smooth muscle

BACKGROUND

The i.v. anaesthetic propofol produces bronchodilatation. Airway relaxation involves reduced intracellular Ca(2+) ([Ca(2+)](i)) in airway smooth muscle (ASM) and lipid rafts (caveolae), and constitutional caveolin proteins regulate [Ca(2+)](i). We postulated that propofol-induced bronchodilatation involves caveolar disruption.

METHODS

Caveolar fractions of human ASM cells were tested for propofol content. [Ca(2+)](i) responses of ASM cells loaded with fura-2 were performed in the presence of 10 µM histamine with and without clinically relevant concentrations of propofol (10 and 30 μM and intralipid control). Effects on sarcoplasmic reticulum (SR) Ca(2+) release were evaluated in zero extracellular Ca(2+) using the blockers Xestospongin C and ryanodine. Store-operated Ca(2+) entry (SOCE) after SR depletion was evaluated using established techniques. The role of caveolin-1 in the effect of propofol was tested using small interference RNA (siRNA) suppression. Changes in intracellular signalling cascades relevant to [Ca(2+)](i) and force regulation were also evaluated.

RESULTS

Propofol was present in ASM caveolar fractions in substantial concentrations. Exposure to 10 or 30 µM propofol form decreased [Ca(2+)](i) peak (but not plateau) responses to histamine by ~40%, an effect persistent in zero extracellular Ca(2+). Propofol effects were absent in caveolin-1 siRNA-transfected cells. Inhibition of ryanodine receptors prevented propofol effects on [Ca(2+)](i), while propofol blunted [Ca(2+)](i) responses to caffeine. Propofol reduced SOCE, an effect also prevented by caveolin-1 siRNA. Propofol effects were associated with decreased caveolin-1 expression and extracellular signal-regulated kinase phosphorylation.

CONCLUSIONS

These novel data suggest a role for caveolae (specifically caveolin-1) in propofol-induced bronchodilatation. Due to its lipid nature, propofol may transiently disrupt caveolar regulation, thus altering ASM [Ca(2+)](i).

Headspace-SPME-GC/MS as a simple cleanup tool for sensitive 2,6-diisopropylphenol analysis from lipid emulsions and adaptable to other matrices

Due to increased regulatory requirements, the interaction of active pharmaceutical ingredients with various surfaces and solutions during production and storage is gaining interest in the pharmaceutical research field, in particular with respect to development of new formulations, new packaging material and the evaluation of cleaning processes. Experimental adsorption/absorption studies as well as the study of cleaning processes require sophisticated analytical methods with high sensitivity for the drug of interest. In the case of 2,6-diisopropylphenol - a small lipophilic drug which is typically formulated as lipid emulsion for intravenous injection - a highly sensitive method in the concentration range of μg/l suitable to be applied to a variety of different sample matrices including lipid emulsions is needed. We hereby present a headspace-solid phase microextraction (HS-SPME) approach as a simple cleanup procedure for sensitive 2,6-diisopropylphenol quantification from diverse matrices choosing a lipid emulsion as the most challenging matrix with regard to complexity. By combining the simple and straight forward HS-SPME sample pretreatment with an optimized GC-MS quantification method a robust and sensitive method for 2,6-diisopropylphenol was developed. This method shows excellent sensitivity in the low μg/l concentration range (5-200μg/l), good accuracy (94.8-98.8%) and precision (intraday-precision 0.1-9.2%, inter-day precision 2.0-7.7%). The method can be easily adapted to other, less complex, matrices such as water or swab extracts. Hence, the presented method holds the potential to serve as a single and simple analytical procedure for 2,6-diisopropylphenol analysis in various types of samples such as required in, e.g. adsorption/absorption studies which typically deal with a variety of different surfaces (steel, plastic, glass, etc.) and solutions/matrices including lipid emulsions.

Clinical effects and lethal and forensic aspects of propofol

Propofol is a potent intravenous anesthetic agent that rapidly induces sedation and unconsciousness. The potential for propofol dependency, recreational use, and abuse has only recently been recognized, and several cases of accidental overdose and suicide have emerged. In addition, the first documented case of murder using propofol was reported a few months ago, and a high profile case of suspected homicide with propofol is currently under investigation. A number of analytical methods have been employed to detect and quantify propofol concentrations in biological specimens. The reported propofol-related deaths and postmortem blood and tissue levels are reviewed. Importantly, limitations of propofol detection are discussed, and future considerations are presented. Because propofol has the potential for diversion with lethal consequences, the forensic scientist must have a basic understanding of its clinical indications and uses, pharmacologic properties, and detection methods. In addition, medical institutions should develop systems to prevent and detect diversion of this potential drug of abuse.

Investigation of Propofol Concentrations in Human Breath by Solid-Phase Microextraction Gas Chromatography–Mass Spectrometry

Propofol has been detected in human breath after being used as an intravenous anaesthetic, and this could provide a noninvasive method for monitoring propofol anaesthesia. The physicochemical properties of propofol allow it to diffuse across the alveolocapillary membrane and to be prepared as a calibration gas. In this study, headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC–MS), coupled with an external standard, was applied to assess propofol levels in the breath and plasma from three subjects under intravenous anaesthesia. Lower quantitation limits were 3.6 ng/l and 0.2 mg/l for propofol analysis in breath and arterial plasma, respectively. Intraday precision and recovery percentages for propofol detection in breath were 4.3-6.7% and 98-108%, respectively, and in plasma they were 3.8-6.1% and 90.1-125.1%, respectively. Propofol concentrations were 4.3-33.5 ng/l in breath and 3.2-6.8 mg/l in arterial plasma. A correlation was shown between propofol concentration in breath and plasma. Thus, HS-SPME-GC–MS, coupled with an external standard, could be a reliable and sensitive analytical technique for detecting propofol in breath during anaesthesia.

Rapid measurement of blood propofol levels: a proof of concept study

OBJECTIVE

Despite many advantages over traditional volatile anaesthetic techniques, propofol total intravenous anaesthesia (TIVA) makes up a small percentage of general anaesthetics administered. One of the reasons for this is the absence of a clinically useful method for measuring blood propofol concentrations. We have designed and tested a prototype system for rapidly measuring blood plasma levels of propofol using solid phase extraction (SPE) methodology, coupled with colorimetric and spectrometric techniques.

METHODS

Multiple venous blood samples were taken from 17 subjects during induction of anaesthesia with propofol. Samples were analysed in duplicate on both the prototype system and using High Performance Liquid Chromatography (HPLC). The prototype monitor response was calibrated against known methanol-based propofol standards and an estimate of the plasma concentration of propofol derived from regression analysis of the standard responses.

RESULTS

Bland Altman analysis from a total of 87 samples gave 95% limits of agreement between the two methods of -0.34 to 0.42 microg mL(-1) (with no significant bias). The mean absolute prediction error was 8.9(7.5)%. The run time per sample on the prototype system was 4.5 min, including sample preparation.

CONCLUSION

The results show that this methodology may be suitable for rapid and accurate clinical monitoring of propofol levels during general anaesthesia.

Mass spectral fragmentation of the intravenous anesthetic propofol and structurally related phenols

Propofol (2,6-diisopropyl phenol) is a widely used intravenous anesthetic. To define its pharmacokinetics and pharmacodynamics, methods for its quantitation in biological matrixes have been developed, but its pattern of mass spectral fragmentation is unknown. We found that fragmentation of the [M - H](-) ion (m/z 177) of propofol in both APCI MS/MS and ESI MS/MS involves the stepwise loss of a methyl radical and a hydrogen radical from one isopropyl side chain to give the most intense product ion, [M -H - CH(4)](-), at m/z 161. This two-step process is also the preferred mode of fragmentation for similar branched alkyl substituted phenols. This mode of fragmentation of the [M - H](-) ion is supported by three independent lines of evidence: (1) the presence of the intermediary [M - H - CH(3)](-) radical ion under conditions of reduced collision energy, (2) the determination of the mass of the predominant [M - H - CH(4)](-) product ion by high resolution mass spectrometry, and (3) the pattern of product ions resulting from further fragmentation of the [M - H - CH(4)](-) product ion. Phenols with a single straight chain alkyl substituent, in contrast, undergo beta elimination of the alkyl radical irrespective of the length of the alkyl chain, yielding the most intense product ion at m/z 106. This product ion represents a special case of a stable intermediary radical for the two-step process described for branched side chains, because further elimination of a hydrogen radical from the beta carbon is not possible.

Determination of thymol in human plasma by automated headspace solid-phase microextraction-gas chromatographic analysis

A reliable and sensitive method was developed for determination of thymol in human plasma by automated headspace solid-phase microextraction (SPME). After enzymatic cleavage of thymol sulfate thymol was extracted by a 65 microm polydimethylsiloxane-divinylbenzene crimped fiber (Supelco) after addition of sodium chloride and phosphoric acid (85%). Desorption of the fiber was performed in the injection port of a gas chromatograph at 220 degrees C (HP 5890; 50 m x 0.2 mm I.D., 0.2 microm HP Innowax capillary column; flame ionization detection). Fibers were used repeatedly up to 40 analysis. The recovery was 5% after 35 min of extraction. The calibration curve was linear in the range of 8.1-203.5 ng ml(-1) with a limit of quantitation (LOQ) of 8.1 ng ml(-1). The within-day and between-day precision and accuracy were < or = 20% at the LOQ and <15% at higher concentrations according to international guidelines for validation of bioanalytical methods. After administration of a thymol-containing herbal extract only thymol sulfate, no free thymol, could be detected in human plasma, thus analysis of thymol was after enzymatic cleavage of thymol sulfate. It is concluded that the newly developed automated method can be used in clinical trials on bioavailability and pharmacokinetics of thymol-containing herbal medicinal products.