Comparison of high-performance liquid chromatography and polyclonal fluorescence polarization immunoassay for the monitoring of midazolam in the plasma of intensive care unit patients

Clinical Pharmacokinetic Monitoring of Midazolam in Critically Ill Patients

Midazolam is a commonly used sedative in critically ill, mechanically ventilated patients in intensive care unit (ICU) settings worldwide. We used a nine-step decision-making algorithm to determine whether therapeutic monitoring of midazolam in the ICU is warranted. Midazolam has a higher clearance and shorter half-life than other benzodiazepines, and prolonged sedation is achieved with continuous infusion. There appears to be very good correlation between plasma concentrations of both midazolam and its active metabolite, alpha1-hydroxymidazolam, and the degree of sedation. However, due to high interpatient variability, it is not possible to predict the level of sedation in any given individual based on plasma concentration of midazolam or its metabolites. Moreover, no simple and practical assay is available to quantitate midazolam plasma concentrations in the acute ICU setting. Many scales are available to assess the sedative effects of midazolam. Because the plasma concentration of midazolam required to achieve a constant level of sedation is highly variable, it is usually more prudent for the clinician to monitor for sedation with a validated clinical scale than by plasma concentrations alone. Various physiologic parameters, including age-related effects, compromised renal function, and liver dysfunction affect the pharmacokinetics of midazolam and alpha1-hydroxymidazolam. Although routine drug monitoring for all critically ill patients receiving midazolam is not recommended, this practice is likely beneficial in patients with neurologic damage in whom sedation cannot be assessed and in patients who have renal failure with a prolonged time to awakening.

Sensitive determination of midazolam and 1′-hydroxymidazolam in plasma by liquid–liquid extraction and column-switching liquid chromatography with ultraviolet absorbance detection and its application for measuring CYP3A activity

This manuscript described a new sensitive determination of midazolam and its metabolite 1'-hydroxymidazolam by automated column-switching high-performance liquid chromatography. The test compounds were extracted from 2 ml of plasma using chloroform-hexane (30:70, v/v) and the extract was injected into a column I (TSK-PW precolumn, 10 microm, 35 mm x 4.6 mm i.d.) for clean-up and column II (C18 STR ODS-II analytical column (5 microm, 150 mm x 4.6 mm i.d.) for separation. The mobile phase for separation consisted of phosphate buffer (0.02 M, pH 4.6), perchloric acid (60%) and acetonitrile (57.9:0.1:42, v/v/v) and was delivered at a flow-rate of 0.6 ml/min. The peak was detected using a UV detector set at 254 nm. The method was validated for the concentration range 0.3-100 ng/ml, and good linearity (r > 0.998) was confirmed. Intra- and inter-day coefficient variations for midazolam and 1'-hydroxymidazolam were less than 8.5 and 6.1%, respectively, at the concentrations of 0.5, 5 and 50 ng/ml for the test compounds. Relative errors ranged from -14 to 6% and mean recoveries were 78-85%. The limit of quantification was 0.5 ng/ml for each compound. This method was sensitive enough for pharmacokinetic studies measuring CYP3A activity in human volunteers following an intravenous (1 mg) and a single-oral administration (2 mg) of a subtherapeutic midazolam dose.

Determination of midazolam in human plasma by solid-phase microextraction and gas chromatography/mass spectrometry

A new method is described for the qualitative and quantitative analysis of midazolam, a short-acting 1,4-imidazole benzodiazepine, in human plasma. It involves a plasma deproteinization step, solid-phase microextraction (SPME) of midazolam using an 85-microm polyacrylate fiber, and its detection by gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring (SIM) mode, using pinazepam as internal standard. The assay is linear over a midazolam plasma range of 1.5-300 ng/mL, relative intra- and inter-assay standard deviations at 5 ng/mL are below 7%, and the limit of detection is 1 ng/mL. The method is simple, fast and sufficiently sensitive to be applied in clinical and forensic toxicology as well as for purposes of therapeutic drug monitoring.

Methods for the measurement of benzodiazepines in biological samples

A review of methods for the measurement of benzodiazepines in biological specimens published over the last five years is presented. A range of immunoassay procedures using EIA, ELISA, FPIA, agglutination or kinetic interaction of microparticles, or RIA methods are now available. Cross reactivities to benzodiazepines are variable such that no one kit will recognise all benzodiazepines and their relevant metabolites at concentrations likely to be encountered during therapeutic use. Prior hydrolysis of urine to convert glucuronide metabolites to immunoreactive substances improves detection limits for many benzodiazepines. Several radioreceptor assays have now been published and show good sensitivity and specificity to benzodiazepines and offer the advantage (over immunoassay) of being able to detect these drugs with equal sensitivity. Solvent extraction techniques using a variety of solvents were still popular and offer acceptable recoveries and lack of significant interference from other substances. A number of papers describing solid phase extraction procedures were also published. Direct injection of specimens into a HPLC column with back flushing were also successfully described. Seventy two chromatographic methods using HPLC, LC-MS, GC and GC-MS methods were reviewed. HPLC was able to achieve detection limits for many benzodiazepines using UV or DAD detection down to 1-2 ng/ml using 1-2 ml of urine or serum (blood). ECD detectors gave detection limits better than 1 ng/ml from 1 ml of specimen, which was an order of magnitude lower than for NPD. EI-MS offered similar sensitivity, whilst NCI-MS was capable of detection down to 0.1 ng/ml. Methods suitable for the separation of enantiomers of benzodiazepines have been described using HPLC. Electrokinetic micellar chromatography has also been shown to be capable of the analysis of benzodiazepines in urine.