Solid-phase microextraction of human plasma samples for determination of sufentanil by gas chromatography-mass spectrometry

A solid-phase microextraction (SPME) method has been developed for the quantitative analysis of sufentanil from human plasma by gas chromatography-mass spectrometry (GC-MS). The immersion SPME sampling technique was optimized for the extraction of sufentanil from plasma. The influence of the pH and the ionic strength of the sample on the extraction of the analytes by the SPME fiber were investigated. Sufentanil and fentanyl (internal standard) were extracted from plasma with a 65-microm polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber for 30 minutes using salting out agents in basic conditions. The calibration curve was linear over a concentration range of 6-50 ng/mL. Intraday and interday relative standard deviations were 3.6% and 10.6%, respectively. The limit of quantification was 6 ng/mL for a plasma volume of 1 mL. With regard to selectivity, simplicity, and low cost, the SPME method described should be useful for a rapid extraction of sufentanil from human plasma.

Intrathecal morphine overdose during combined spinal-epidural block for Caesarean delivery

We describe a 25 mg intrathecal morphine overdose during a combined spinal-epidural block for a Caesarean delivery. Naloxone infusion (5.24 mg over 24 h) was started prior to the patient becoming symptomatic and almost immediately after the overdose. Invasive therapeutics such as mechanical ventilation were avoided.

Postdelivery of alfentanil and ketamine has no effect on intradermal capsaicin-induced pain and hyperalgesia

OBJECTIVE

The predelivery of intravenous alfentanil (a mu opioid agonist) and ketamine (an -methyl d-aspartate antagonist) has recently been shown to decrease the secondary hyperalgesia induced by intradermal capsaicin. The focus of this study was to determine the effects of the postdelivery of intravenous alfentanil and ketamine on intradermal capsaicin-induced secondary hyperalgesia.

DESIGN

Double-blind, placebo-controlled, randomized, crossover study. Five minutes after an intradermal capsaicin injection, alfentanil and ketamine infusions were administered for a target plasma concentration of 75 ng/ml for alfentanil and 150 ng/ml for ketamine or placebo equivalent using a computer-controlled infusion pump and maintained for the remainder of the study. The investigator recorded the magnitude of the pain score at the time of injection and at 5-minute intervals. Fifteen minutes after the intradermal capsaicin injection, the region of secondary hyperalgesia and flare response was determined.

RESULTS

Alfentanil and ketamine plasma levels targeted after injection of intradermal capsaicin had no significant effect on pain scores, flare response, or secondary hyperalgesia.

CONCLUSIONS

Consistent with animal studies on preemptive analgesia, this study demonstrates that alfentanil and ketamine have a differential effect when delivered before and after a painful stimulus. Because of the differential effect seen, future studies on the pharmacology of human experimental pain should evaluate both predrug and postdrug delivery.

Sequential first-pass metabolism of nortilidine: the active metabolite of the synthetic opioid drug tilidine

The disposition of nortildine, the active metabolite of the synthetic opioid drug tilidine, was investigated in healthy volunteers in a randomized, single-dose, three-way crossover design. Three different treatments were administered: tilidine 50 mg intravenously, tilidine 50 mg orally, and nortilidine 10 mg intravenously. The plasma concentrations of tilidine, nortilidine, and bisnortilidine were determined and subjected to pharmacokinetic analysis using noncompartmental methods. The systemic bioavailability of tilidine was low (7.6% +/- 5.3%) due to a pronounced first-pass metabolism. The areas under the plasma concentration versus time curves (A UC) of nortilidine were similar following either oral or intravenous administration of tilidine 50 mg (375 +/- 184 vs. 364 +/- 124 ng.h.ml(-1)). AUC of nortilidine was 229 +/- 42 ng.h.ml(-1) after IV infusion of nortilidine 10 mg and thus much greater than after IV tilidine corrected for differences in dose. Nortilidine had a much lower volume of distribution (275 +/- 79 vs. 1326 +/- 477 L) and a somewhat lower clearance (749 +/- 119 vs. 1198 +/- 228 ml/min) than tilidine. About two-thirds of the dose of tilidine was metabolized to nortilidine, although only half of the latter fraction was available in the peripheral circulation. Nortilidine was subsequently metabolized to bisnortilidine. The mean ratio of the AUC of bisnortilidine to nortilidine was 0.65 +/- 0.14 following IV administration of nortilidine but 1.69 +/- 0.38 and 1.40 +/- 0.27 following oral and intravenous administration of tilidine, respectively. The shapes of the plasma concentration-time curves of the metabolites and parent drug declined in parallel, indicating that the disposition of the metabolites is formation rate limited. Thus, although two-thirds of the dose of tilidine is metabolized to nortilidine, only one-third of the dose is available systemically as nortilidine for interaction with the opiate receptors after both intravenous and oral dosing of tilidine. The remaining part of nortilidine is retained in the liver and is subsequently metabolized to bisnortilidine and yet unknown compounds.

The magnitude of acute tolerance to morphine analgesia: concentration-dependent or time-dependent?

We evaluated the relationship of either the infusion time or the plasma morphine concentrations on the magnitude of acute tolerance to morphine analgesia. Male New Zealand White rabbits were randomly allocated to one of four groups. Group 1 received an IV bolus of morphine 40 mg followed by an infusion at 20 mg/h for 8 h. Group 2 received a 20-mg morphine bolus followed by an infusion at 10 mg/h. Group 3 received a 10-mg morphine bolus followed by an infusion at 5 mg/h. Group 4 received a saline bolus and infusion. Analgesia was determined by the paw-pressure test, and the plasma concentrations of morphine were measured by high-performance liquid chromatography. We found that the plasma concentrations of morphine were maintained at a steady-state between 2 and 8 h after the morphine administration. However, from 2 to 8 h after the morphine infusion, the longer the infusion time was, the less the analgesic effect remained. Furthermore, the magnitude of acute tolerance was significantly correlated to the duration of morphine infusion (r = 0.93; P < 0.01) but not the different steady-state plasma morphine concentrations. We conclude that the magnitude of morphine tolerance is significantly correlated to the duration of infusion but not the different steady-state plasma morphine concentrations.

IMPLICATIONS

We evaluated the relationship of either the infusion time or the plasma morphine concentrations on the magnitude of acute tolerance to morphine analgesia in rabbits. We found that the magnitude of morphine tolerance is significantly correlated to the duration of infusion but not to the different steady-state plasma morphine concentrations.

A new series of 13 buprenorphine-related deaths

OBJECTIVES

Buprenorphine at high dosage became available in France in 1996, as a substitution treatment for heroin addicts. Since this date, numerous deaths were attributed to this drug. This paper reports a new series of 13 fatalities involving buprenorphine observed at the Institute of Legal Medicine of Strasbourg, between August 2000 to October 2001.

DESIGN AND METHODS

During the mentioned period, about 800 forensic cases were screened at the laboratory. Buprenorphine and its primary metabolite norbuprenophine were assayed in postmortem specimens by HPLC/MS. From these 13 subjects, 11 were male. Blood levels ranged from 0.3 to 7.7 ng/mL (mean 3.5 ng/mL) and 0.3 to 16.2 ng/mL (mean 2.9 ng/mL) for buprenorphine and norbuprenorphine, respectively. The mean values appear to be within the therapeutic range.

CONCLUSIONS

IV injection of crushed tablets, a concomitant intake of psychotropics (especially benzodiazepines and neuroleptics) and the high dosage of the buprenorphine formulation available in France appear as the major risk factors for such fatalities.

Morphine glucuronide-to-morphine plasma ratios are unaffected by the UGT2B7 H268Y and UGT1A1*28 polymorphisms in cancer patients on chronic morphine therapy

OBJECTIVE

UDP-glucuronosyltransferase (UGT) 2B7 is the major UGT isoform responsible for the 3- and 6-glucuronidation of morphine in humans. Studies in rats have indicated that UGT1A1 may also contribute to the formation of morphine 3-glucuronide (M3G). Our objective was to investigate whether the UGT2B7 H268Y and UGT1A1*28 polymorphisms contribute to the variability in morphine glucuronide-to-morphine plasma ratios among cancer patients undergoing analgesic therapy with morphine.

METHODS

Seventy patients with normal hepatic and renal function using slow-release morphine to relieve cancer pain were included. UGT2B7 genotyping was performed using restriction enzyme analysis of polymerase chain reaction (PCR)-amplified DNA fragments. Wild-type and variant alleles of the UGT1A1 gene were identified using sizing of PCR-amplified fragments. Morphine 6-glucuronide (M6G)/morphine, M3G/morphine, and M3G/M6G plasma ratios were compared between genotypes.

RESULTS

The M3G/morphine, M6G/morphine, and M3G/M6G plasma ratios varied 16-, 42-, and sevenfold, respectively, among individuals. No statistically significant differences in plasma ratios were found between individuals possessing UGT2B7 H/H ( n=20), H/Y ( n=30), or Y/Y ( n=20) genotypes. Five patients were homozygous for the UGT1A1 TA(7) allele, which is associated with reduced UGT1A1 gene expression. However, the mean M3G/M6G and M3G/morphine plasma ratios in TA(7) homozygous subjects did not differ significantly from those of heterozygous or homozygous wild-type (TA(6)) individuals.

CONCLUSION

The UGT2B7 H268Y polymorphism cannot account for the considerable variation in glucuronide-to-morphine ratios in cancer patients. Moreover, the contribution of UGT1A1 to the formation of M3G appears to be of minor biological significance, at least in a UGT2B7 background.

Minimal interaction between gatifloxacin and oxycodone

Previous studies have demonstrated a significant reduction in the oral bioavailability of trovafloxacin and ciprofloxacin when administered concomitantly with an intravenous opiate, such as morphine. This decrease in absorption results in a 36% and 50% lower AUC for trovafloxacin and ciprofloxacin, respectively, which could cause clinical failures. The authors investigated the possibility of a similar interaction between oxycodone and gatifloxacin. Twelve healthy volunteers were randomized in an open-label, two-way crossover study to receive oxycodone (5 mgpo Q4H) andgatifloxacin (400 mg po 1 h) after starting the oxycodone or gatifloxacin 400 mg po alone. Blood samples were drawn at 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 18, and 24 hours postdosing. No significant difference was noted (p > 0.05) in AUC (31.6 +/- 7.3 vs. 31.7 +/- 7.1) and Cmax (3.2 +/- 0.6 vs. 3.0 +/- 0.6) for gatifloxacin versus gatifloxacin/oxycodone regimens; however, the tmax (1.8 +/- 0.8 vs. 4.3 +/- 1.5) was significantly delayed (p < 0.001). It was concluded that oral oxycodone and gatifloxacin can be administered concomitantly without a significant decrease in bioavailability.

Determination of remifentanil in human blood by capillary gas chromatography with nitrogen-selective detection

A validated method for the determination of remifentanil in human blood, applicable to all therapeutic concentrations, using capillary GC with nitrogen-specific detection and fentanyl as the internal standard has been developed. Citrated whole blood samples were extracted into 1-chlorobutane following precipitation of proteins with methanol. The drugs were back extracted into 10 mM HCl and re-extracted into methanol-1-chlorobutane. The extracts were reconstituted in methanol and injected onto a 25-m BPX-5 column. The lower limit of quantitation was 0.2 ng/ml with within- and between-day coefficients of variation of less than 15%.

Validation and application of a sensitive assay for butorphanol in human plasma by high-performance liquid chromatography with tandem mass spectrometry detection

A sensitive and convenient high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay for the opioid receptor agonist-antagonist butorphanol in human plasma is described. BC-2605, a cyclopropyl analogue of butorphanol, was employed as an internal standard. Butorphanol was recovered from plasma (84.4 +/- 10.9%) by liquid-liquid extraction. The mobile phase flow-rate was 0.3 ml/min and consisted of methanol-water-formic acid (90:10:0.1, v/v/v). The analytical column (4.6 x 100 mm) was packed with Partisil C(8) (5 microm). The standard curve was linear from 13.7 to 1374 pg/ml (r(2)>0.99). The lower limit of quantitation was 13.7 pg/ml. The assay was specific, accurate (% deviation from nominal concentrations were <15%), precise and reproducible (within- and between-day coefficients of variation <7%). Butorphanol in plasma was stable over 3 freeze/thaw cycles and at room temperature for 1 day. The utility of the assay was demonstrated by following butorphanol plasma concentrations in two healthy subjects for 24 h following a 1 mg intranasal dose.

[Analytical problems in examination of small amounts of blood samples taken from law offenders]

In the paper there have presented results of the analysis of small blood samples taken routinely from 3 cases after car accidents and 1 rapist. Fluorescence polarisation immunoassay (FPIA, Abott) was used for screening examinations of narcotics from the group of both opium and cocaine alkaloids, barbituric acid and benzodiazepine and also drugs from the group of tricyclic antidepressants. Confirmation of the obtained results and full identification of the substances analysed were carried out by liquid chromatography with mass spectrometry (LC-MS). In the causes of car accidents components of "compote" were found (poppy straw extract) morphine and codeine (1 case), cocaine (1 case) and also tramadol and diazepam (1 case) were also found. In the rapist methylenedioxymethamphetamine (MDMA) was determined.

Pre-emptive effect of epidural sufentanil in abdominal hysterectomy

BACKGROUND

Experimental studies suggest pre-emptive administration of analgesics is effective but clinical evidence is less convincing.

METHODS

Forty-one patients undergoing abdominal hysterectomy were allocated randomly in a double-blind fashion to receive sufentanil 50 micrograms via a lumbar epidural catheter before or at the end of surgery.

RESULTS

Sufentanil consumption from a patient-controlled epidural analgesia (PCEA) system and numerical pain scores at rest and during movement over the initial 72 h were similar in the two groups. When the study period was divided into five time intervals, sufentanil consumption in the pre-emptive group was significantly less than in the control group between 8 and 16 h after surgery (P = 0.04). Furthermore, the number of failed bolus attempts from the PCEA device was significantly lower and patient satisfaction was significantly better in the pre-emptive group during the 72 h of PCEA treatment (P < 0.05). In addition, the median decrease in ACTH and cortisol on the first postoperative morning relative to baseline values was greater in the pre-emptive group than in the control group (P < 0.05). In subjects who had a Pfannenstiel incision, touch and pain sensitivity in the wound area were less in the pre-emptive group over the first 4 postoperative days (P < 0.05).

CONCLUSIONS

We conclude that pre-emptive analgesia with epidural sufentanil was associated with a short-term sufentanil-sparing effect, and could have reduced stress hormone responses and wound sensitization after abdominal hysterectomy.

Method development and validation of a high-performance liquid chromatographic method for tramadol in human plasma using liquid-liquid extraction

An HPLC system using a simple liquid-liquid extraction and HPLC with UV detection has been validated to determine tramadol concentration in human plasma. The method developed was selective and linear for concentrations ranging from 10 to 2000 ng/ml with average recovery of 98.63%. The limit of quantitation (LOQ) was 10 ng/ml and the percentage recovery of the internal standard phenacetin was 76.51%. The intra-day accuracy ranged from 87.55 to 105.99% and the inter-day accuracy, 93.44 to 98.43% for tramadol. Good precision (5.32 and 6.67% for intra- and inter-day, respectively) was obtained at LOQ. The method has been applied to determine tramadol concentrations in human plasma samples for a pharmacokinetic study.

Morphine responsiveness in a group of well-defined multiple sclerosis patients: a study with i.v. morphine

Pain in multiple sclerosis (MS) is more common than has previously been believed. About 28% of all MS patients suffer from central pain (CP), a pain that is difficult to treat. In the present study we have investigated the responsiveness of this pain to morphine. Fourteen opioid-free patients (eight woman and six men) with constant, non-fluctuating, long-lasting CP caused by MS were investigated. Placebo (normal saline), morphine and naloxone were given intravenously in a standardized manner. The study design was non-randomized, single blind and placebo controlled. Ten patients experienced less than 50% pain reduction by placebo and less than 50% pain reduction by morphine. Four patients were opioid responders, i.e. had minimal or no effect on pain by placebo, >50% pain reduction after morphine and >25% pain increase after naloxone, given intravenously following morphine. However, this response was obtained after high doses of morphine (43 mg, 47 mg, 50 mg and 25 mg; mean 41 mg). Thus, compared with nociceptive pain, only a minority of the patients with CP due to MS responded to morphine and only at high doses. The present results are in accord with experimental studies indicating that neuropathic pain is poorly responsive but not totally unresponsive to opioids. The results do not support the routine use of strong opioids in MS patients with CP.

Absence of opioid withdrawal symptoms in patients receiving methadone and the protease inhibitor lopinavir-ritonavir

A study was designed to determine the interactions, both clinical and pharmacokinetic, between methadone and lopinavir-ritonavir. Results demonstrated a 36% reduction in the methadone area under the plasma concentration-time curve after the introduction of lopinavir-ritonavir, with no coincident symptoms of opioid withdrawal and no requirement for methadone dose adjustment.

The bioavailability and pharmacokinetics of subcutaneous, nebulized and oral morphine-6-glucuronide

AIMS

Morphine-6-glucuronide (M6G), one of the active metabolites of morphine, has attracted considerable interest as a potent opioid analgesic with an apparently superior therapeutic index. To date studies have used the intravenous route, which is generally unacceptable in the treatment of cancer related pain. The aim of this study was to define the pharmacokinetics, toxicity and cardio-respiratory effects of three alternative routes of administration of M6G.

METHODS

Ten healthy volunteers participated in an open randomized study. Subjects received M6G 2 mg as an intravenous bolus, 20 mg orally, 2 mg subcutaneously and 4 mg by the nebulized route. Pulse, blood pressure, respiratory rate and peak flow rate were monitored and subjective toxicity recorded on rating and visual analogue scales.

RESULTS

After i.v. M6G the mean (+/- s.d.) AUC(0,infinity) standardized to a dose of 1 mg was 223 +/- 57 nmol l(-1) h, mean elimination half-life was 1.7 +/- 0.7 h and the mean clearance was 157 +/- 46 ml min(-1). These parameters were virtually identical after subcutaneous administration which had a bioavailability (F(0,infinity)) of 102 +/- 35% (90% CI 82, 117%) and t(max) of 0.5 +/- 0.2 h. The mean bioavailability of nebulized M6G was 6 +/- 2% (90% CI 4, 7%) with a t(max) of 1.2 +/- 0.8 h. Following oral M6G two plasma M6G peaks were seen in 7 of the 10 subjects, the first with a t(max) of 3.1 (+/- 0.9) h. The second peak had a t(max) of 13.4 (+/-5.0) h, started approximately 4 h after dosing, and was associated with the detection of plasma M3G and morphine, suggesting that M6G was significantly hydrolysed in the gut to morphine, which was then glucuronidated following absorption. Although the overall mean bioavailability was 11 +/- 3% (90% CI 9, 12%), confining the analysis to data from the first peak suggested a bioavailability of directly absorbed M6G of only 4 +/- 4%. Apart from a characteristic dysphoria following intravenous and subcutaneous M6G, there was no significant toxicity.

CONCLUSIONS

With the minimal toxicity reported in this and previous studies, subcutaneous infusion of M6G may potentially provide clinically useful analgesia for advanced cancer pain. Nebulized M6G is not significantly absorbed via the lungs, and if opiates are shown to have a local effect in the lung, reducing the sensation of breathlessness, then nebulized administration is likely to minimize systemic effects. Oral M6G has poor bioavailability, but is significantly hydrolysed in the gut to morphine, which is subsequently glucuronidated following absorption. This circuitous route accounts for the majority of systemically available M6G after oral administration.

Validation of fentanyl pharmacokinetics in patients undergoing coronary artery bypass grafting

PURPOSE

The current emphasis on more rapid recovery and earlier tracheal extubation after cardiac surgery requires greater precision in administering opioids to reap their benefits while minimizing the duration of postoperative respiratory depression. Therefore, we aimed to define a pharmacokinetic model that accurately predicts fentanyl concentrations before, during, and after cardiopulmonary bypass (CPB) in patients undergoing coronary artery bypass grafting (CABG).

METHODS

Parameters for two-compartment and three-compartment models were estimated by applying population pharmacokinetic modelling to fentanyl concentration vs time data measured in 29 patients undergoing elective, primary CABG. The ability of these models to predict fentanyl concentrations in a second series of ten patients undergoing CABG was then assessed.

RESULTS

A simple, three-compartment model had excellent predictive ability, with a median prediction error (PE = ([Fentanyl]meas - [Fentanyl]pred)/[Fentanyl]pred x 100%) of -0.5%, and a median absolute PE (APE = /PE/) of 14.0%. In comparison to the two-compartment models, linear regression of measured:predicted concentration ratios indicated that the three-compartment model was free of systematic and time-related changes in bias (P < 0.05). The parameters of this three-compartment model are: V1 15.0 l, V2 20.0 l, V3 86.1 l, Cl1 1.08 L x min(-1), Cl2 4.90 L x min(-1), and Cl3 2.60 L x min(-1).

CONCLUSIONS

Our pharmacokinetic model provides a rational foundation for designing fentanyl dose regimens for patients undergoing CABG. When combined with previously published information regarding intraoperative fentanyl pharmacodynamics, dose regimens that reliably achieve and maintain desired fentanyl concentrations throughout the intraoperative period can be designed to achieve specific therapeutic goals.

Characterization of the pharmacokinetics of buprenorphine and norbuprenorphine in rats after intravenous bolus administration of buprenorphine

The purpose of this project was to characterize the dose-dependent pharmacokinetics of buprenorphine (BN) and norbuprenorphine (NBN), the primary metabolite, after intravenous administration of different doses of BN to rats. Adult male Sprague-Dawley rats were divided into six groups and received a single intravenous bolus dose of 0.1, 0.3, 1, 3, 10 or 30 mg/kg of BN. A separate study was performed where BN and NBN were simultaneously administered intravenously (1 mg/kg+1 mg/kg). Plasma samples were obtained by centrifugation of the blood and analyzed for BN and NBN using a sensitive and selective gas chromatographic-mass spectrometric (GC-MS) bio-analytical method. Noncompartmental and compartmental methods were used to perform pharmacokinetic data analysis. BN declined triexponentially with a dose-dependent increase in its volume of distribution, V(ss) (8.37-18.2 l/kg) and clearance CL (2.70-6.10 l/h per kg). The pharmacokinetics of NBN were linear and biexponential. Coadministration of BN and NBN resulted in a significant increase in the volume of distribution and clearance of BN. The present results suggest that the nonlinear disposition in the clearance and volume of distribution of BN can be attributed, in part, to the increasing concentration of the metabolite.

Differential tramadol and O-desmethyl metabolite levels in brain vs. plasma of mice and rats administered tramadol hydrochloride orally

OBJECTIVE

To investigate a possible differential brain uptake of tramadol vs. its major metabolite (O-desmethyl tramadol; M1) in mice and rats.

METHODS

An extraction and measurement technique (gas chromatograph equipped with a nitrogen phosphorus detector) was used to measure plasma and brain levels of tramadol and M1 at intervals 10-300 min after oral dosing of tramadol hydrochloride to mice and rats.

RESULTS

For all doses of tramadol administered (5, 10, 20, or 40 mg/kg), tramadol and M1 plasma levels were greatest 10 min after dosing: in mice, peak tramadol plasma levels were 47.75-736.72 ng/mL and peak M1 levels were 75.30-1084.92 ng/mL; in rats, peak tramadol plasma levels were 185.03-455.81 ng/mL and peak M1 levels were 106.74-455.70 ng/mL. Tramadol brain levels were also greatest 10 min after dosing. In mice, peak tramadol brain levels were 226.42-1847.46 ng/g. Peak M1 levels (72.17-572.97 ng/g) occurred 20-60 min after dosing. In rats, peak tramadol brain levels were 258.50-1777.37 ng/g and peak M1 levels were 80.35-289.60 ng/g. In mice, the ratio of tramadol/M1 in plasma was 0.5-1.0 throughout the measurements, whereas the ratio in brain was about 10 at 10 min and about 2 from 20 to 50 min. In rats, the ratio of tramadol/M1 in plasma was 0.5-1.5, whereas the ratio in brain was about 15 at 10 min and about 4-7 thereafter.

CONCLUSION

In mice and rats, there appears to be preferential brain vs. plasma distribution of tramadol over M1.