Determination of fentanyl in whole blood at subnanogram concentrations by dual capillary column gas chromatography with nitrogen sensitive detectors and gas chromatography/mass spectrometry

Two methods for the determination of fentanyl at subnanogram concentrations in whole blood have been developed and evaluated. The initial screening was by gas chromatography with nitrogen sensitive detection (GC/NPD) in a splitless injection onto two fused-silica, 0.32-mm i.d. capillary columns (5% and 50% phenyl methyl silicone). Confirmation was by gas chromatography/mass spectrometry (GC/MS) using selected ion monitoring of a splitless injection onto a 0.1-mm i.d., 0.34-microns 5% phenyl methyl silicone capillary column. The methods were studied at fentanyl concentrations over the range 0.05 to 5.0 ng/mL using 2 mL of blood. The detection limits were set at 0.10 ng/mL for GC/NPD and 0.05 ng/mL for GC/MS. The overall recovery of fentanyl was found to be greater than 75% over the range of 0.25 to 2.5 ng/mL. The within-run precision determined at fentanyl concentrations of 0.25 and 1.0 ng/mL showed coefficients of variation ranging from 8.7 to 14.8%. The between-run precision determined at concentrations of 0.4 and 0.8 ng/mL showed coefficients of variation ranging from 3.3 to 11.6%. The blood calibration curves in the range of 0.25 to 2.5 ng/mL monitored over a 3-month period showed a mean correlation coefficient of 0.99 for both the GC/NPD and GC/MS methods.

The analysis of several nonopiate narcotic analgesics and cocaine in serum using high-performance liquid chromatography

This paper describes a procedure for the quantitative determination of methadone, meperidine, normeperidine, pentazocine, propoxyphene, norpropoxyphene, and dextromoramide in serum down to levels of 10 micrograms/L and of cocaine down to 25 micrograms/L. The procedure involves a simple extraction technique and high-performance liquid chromatography and is suitable for use in overdose drug screening, forensic toxicology, therapeutic drug monitoring, and pharmacokinetic studies.

Opioid pharmacokinetics in relation to their effects

The chemical structure of drug molecules determines their fundamental pharmacological properties by 'fit' to the receptor, but the physicochemical properties, particularly lipid solubility and fraction un-ionised, dominate in determining distribution in the body and the rate of access to the biophase containing the drug receptors. For example, fentanyl appears much more potent than morphine because similar effective biophase concentrations are achieved with much smaller doses. Pharmacokinetic and pharmacodynamic investigations of the relationships between dose and the time-courses of blood concentrations and pharmacological effects of opioid drugs have helped explain the commonly observed variability between patients and have been useful in deriving effective dosage regimens of opioids such as pethidine, morphine, fentanyl and methadone where blood concentrations are a determinant of pharmacological response and 'target' analgetic blood opioid concentrations have been identifiable. However, there are instances when blood opioid concentrations are not determinants of the analgetic response. Examples include opioids, such as buprenorphine, for which the drug-receptor dissociation rate determines the duration of action, heroin which first has to be metabolised to become an agonist, pentazocine which is an agonist at some opioid receptors and an antagonist at others, and opioids placed intra-spinally acting on receptors in the spinal cord.

Narcotic pharmacokinetics and dynamics: the basis of infusion applications

Morphine, pethidine and fentanyl have similar pharmacokinetic profiles with moderately long elimination half-lives (3 to 4 hours), large steady-state volumes of distribution (2 to 4 l/kg), and high hepatic clearances (10 to 20 ml/kg/min). Alfentanil has a shorter terminal elimination half-life (1 1/2 hours) because of a decreased steady-state volume of distribution (0.5 to 1 l/kg). Physicochemical properties and blood:brain tissue solubility can explain the clinical differences in the rate of onset and dissipation of narcotic effect for these four narcotics. Morphine's low lipid solubility and limited rate of blood:brain barrier penetration results in the slow onset and dissipation of narcotic effect relative to pethidine or fentanyl. Alfentanil's lower blood:brain solubility results in the very rapid onset of narcotic effect when compared to fentanyl. All of the narcotics have a very steep blood concentration:narcotic effect curves. Thus, small changes of narcotic blood concentrations can have profound changes of narcotic effect. Finally, different degrees of perioperative stimuli result in different narcotic blood concentration requirements. Thus, narcotic infusion rates need be varied during surgical procedures to adjust for the varying opiate requirement.

Stereospecific opiate binding in living human polymorphonuclear leucocytes

Living human polymorphonuclear leucocytes were incubated with various opiate agonists and antagonists in radioreceptor assays. Binding of the opiate antagonists 3H-naloxone and 3H-diprenorphine and of the benzomorphan 3H-ethylketocyclazocine was found at 4 degrees C and at 37 degrees C, 3H-naloxone binding was stereospecific. Binding of the opiate agonist 3H-dihydromorphine was present at 37 degrees C but not at 4 degrees C and had a different time course as compared to the antagonists. At both temperatures no specific binding of the proteolytic stable analogue 3H-D-Ala-D-Leu-enkephalin was found. Autoradiography showed an unspecific accumulation of 3H-naloxone inside the cells and a specific localization of grains at the cell membrane.

[Clinical experiences with the short-acting opioid alfentanil (Rapifen)]

Alfentanil (R 39 209, Rapifen), a new short-acting narcotic analgesic, has been used in five modifications of routine anaesthesia. The results of these observations are discussed, as well as the haemodynamic and pharmacokinetic data reported in literature. Rapid onset and short duration of action due to a short elimination half-life time and a low distribution volume offer new possibilities in anaesthesiology. In premedicated patients the drug provides analgesia for very short lasting procedures and can supplement hypnotics like etomidate, short-acting barbiturates and benzodiazepines, e.g. midazolam. Thus it becomes possible to obtain a very pleasant anaesthesia under controlled or assisted ventilation with nitrous oxide/oxygen for procedures of a short or mean duration without further need for volatile anaesthetics.

Pharmacokinetics as applied to total intravenous anaesthesia. Practical implications

In six patients undergoing gynaecological surgery computer assisted total intravenous anaesthesia (CATIA) was performed using etomidate and alfentanil. Constant plasma levels of etomidate (0.3 microgram/ml) from the very beginning onwards were achieved using the so called B.E.T. infusion scheme. Alfentanil plasma concentrations of 0.45 microgram/ml were maintained by the same infusion scheme beginning with skin incision until 20 minutes prior to the end of surgery. The proposed concept of CATIA provided an adequate analgesic and hypnotic effect during anaesthesia for abdominal surgery with a recovery period of short duration.

Simultaneous determination of ketobemidone and its N-demethylated metabolite in patient plasma samples by gas chromatography mass spectrometry with selected ion monitoring

An analytical procedure has been developed for the simultaneous determination of ketobemidone and its N-demethylated metabolite, norketobemidone. After isolation from plasma and re-extraction to acidic aqueous phase, the two aminophenols were extracted as ions pairs with tetrabutylammonium to dichloromethane, where derivatization with ethyl chloroformate took place. Determination was performed by gas chromatography mass spectrometry with selected ion monitoring. Ketobemidone and norketobemidone could be detected in plasma in a concentration of 1 ng ml-1 and 3 ng ml-1, respectively. Determinations were performed down to 5 ng ml-1. The relative standard deviation of the method in the analysis of 10 ng ml-1 of ketobemidone and norketobemidone, respectively, was 8% and 9% (n=10). The absolute recovery of unconjugated ketobemidone and norketobemidone through the method at the 100 ng ml-1 level was 91% and 85%, respectively. The method was applied to the determination of ketobemidone and norketobemidone in plasma from patients given ketobemidone. The concentrations of unconjugated norketobemidone was too small to be detected.

The pharmacokinetics of alfentanil (R39209): a new opioid analgesic

The pharmacokinetics of alfentanil (R39209), a new short-acting opioid analgesic, have been studied in eleven patients. Six patients were given 50 micrograms/kg alfentanil and five patients 125 micrograms/kg as an intravenous bolus injection. Plasma concentrations were measured at intervals up to 6 h (50 micrograms/kg) or 8-10 h (125 micrograms/kg), using a specific radioimmunoassay technique. Plasma concentrations declined triexponentially in both groups. The initial elimination of alfentanil from the plasma was very rapid with 90% of the administered dose leaving the plasma within 30 min. The average half-lives for the three phases were similar for both groups. The combined mean (+/- SEM) half-lives for the 11 patients for the rapid and slow distribution phases were short (t 1/2 pi = 1.2 +/- 0.26 min, t 1/2 alpha = 11.6 +/- 1.63 min). The elimination half-life, t 1/2 beta was 94 +/- 5.87 min which is considerably shorter than that of other opioids. The mean (+/- SEM) total body clearance was 6.4 +/- 1.39 ml . kg-1 . min-1 and the volume of distribution (Vd) was 0.86 +/- 0.194 l/kg. The latter is considerably less than reported values for the chemically related drug, fentanyl, and suggests that alfentanil may have a lower tissue binding affinity than fentanyl. The rapid elimination and short duration of clinical action suggests the feasibility of repeated administration of alfentanil and its use by continuous intravenous infusion.

Pharmacokinetics of alfentanil in man

The distribution and elimination kinetics of alfentanil, a new short-acting analgesic, were studied in five surgical patients. Its behavior, following a bolus injection of 120 micrograms/ml, was compatible with a three-compartment open-model distribution. The disappearance of the drug from plasma was rapid (t 1/2 pi = 3.5 +/- 1.3 minutes, t 1/2 alpha = 16.8 +/- 6.4 minutes) with 96.4% of the drug eliminated from plasma in 1 hour, indicating extensive transfer to the remote peripheral compartment. This was followed by a slower elimination phase with a t 1/2 beta of 94 +/- 38 minutes. Total volume of distribution was 1.03 +/- 0.50 L/kg. Total plasma clearance was 456 +/- 155 ml/min. The short analgesic effect of this drug might be attributed to the rapid displacement of the drug from the central and intermediate compartments to the remote peripheral compartment. Approximately 25% of the injected dose was present in the remote peripheral compartment 30 to 60 minutes after alfentanil administration. As the return of drug from this peripheral to the central compartment is slower than the elimination rate of the drug, it could be the rate-limiting step in the elimination of alfentanil from the body.

Comparative pharmacokinetics of fentanyl and alfentanil

The pharmacokinetics of fentanyl and alfentanil were compared by the simultaneous i.v. administration of both drugs, measurement of plasma concentrations and compartmental analysis. In addition, plasma protein binding, erythrocyte:plasma partition, and heptane:water partition were compared. Alfentanil was found to have a very much smaller apparent volume of distribution, smaller total clearance, and shorter terminal half-time in plasma. Alfentanil was also found to have a greater plasma protein binding, but in contrast to fentanyl, no binding to erythrocytes. It is concluded that alfentanil is less cumulative than fentanyl, has restricted hepatic clearance, and will exhibit non-linear kinetics at very high doses. An appendix describes the model-fitting procedure in detail.

Radioimmunological screening and gas chromatographic determination of morphine and related narcotic analgesics in post mortem blood

A sensitive, reproducible, and relatively specific procedure is presented for the screening, identification, and quantitation of morphine, hydromorphone, codeine, oxycodone, and hydrocodone in autopsy blood. The drugs are isolated from whole blood by adsorption on an XAD-2 resin slurry and subsequent elution with an organic solvent mixture. Part of the resin extract is screened for morphine and related cross-reacting compounds by a commercially available radioimmunoassay (RIA) and the remainder of the same extract is analyzed by gas chromatography using a nitrogen/phosphorus detector (GC/NP). The procedure has been used frequently in forensic toxicological casework. Since toxic blood concentrations of hydrocodone have not been well documented, the results of toxicological examination of two fatalities involving this drug are presented.

Gas chromatographic determination of fentanyl and its analogues in human plasma

There is currently no published chromatographic assay for the fentanyl family of analgesics. This study reports the development of a sensitive, precise, and accurate gas chromatographic method for the determination of fentanyl and its analogues in human plasma. Sensitivity attained for fentanyl and sufentanil was 0.1 ng/mL plasma with an average coefficient of variation of 4.5%. Calibration curve correlation coefficients of 0.99% or greater were consistently obtained. Average recovery of drug into the final extract exceeded 80% and was independent of fentanyl concentration. The required degree of specificity was obtained by selective extraction, use of the nitrogen/phosphorous detector, and chromatographic resolution. This method appears suitable for clinical studies of fentanyl and its derivatives in man.