The mu-opioid agonist remifentanil attenuates hyperalgesia evoked by blunt and punctuated stimuli with different potency: a pharmacological evaluation of the freeze lesion in humans

Experimental pain models inducing hyperalgesia, i.e. an increased sensitivity to noxious stimuli often present in clinical pain, are important tools for studying antinociceptive drug profiles. The correct interpretation of results obtained in these models necessitates their mechanistic understanding. This study evaluated the freeze lesion, an experimental model of hyperalgesia, in humans. Twelve healthy subjects were tested with mechanical (brush, punctuated and blunt) and electrical (5, 250, and 2000 Hz sine wave current) stimuli before and after freezing the skin, and during a computer-controlled infusion of the mu-opioid agonist remifentanil targeting five different plasma concentrations between 0 and 6 ng/ml in a two-staged, single occasion, randomized, and double blind study design. Pharmacodynamic modeling techniques were used to describe the effect of freezing and drug administration on the mechanical and electrical pain thresholds. Freezing the skin resulted in hyperalgesia to blunt and punctuated stimuli and lowered the respective pain threshold by 29 and 73%. Hyperalgesia to brushing or electrical stimuli was not detected. Remifentanil attenuated hyperalgesia to blunt stimuli about twice as potently as hyperalgesia to punctuated stimuli, as indicated by a significantly steeper linear relationship between the remifentanil plasma concentration and the increase of the pain threshold to blunt stimuli. Remifentanil attenuated electrical pain with greater potency for low frequency stimulation. The potency difference of remifentanil suggests that different neuronal mechanisms mediate hyperalgesia to blunt and punctuated stimulation. Absence of brush-evoked and electrical hyperalgesia is compatible with the view that mechanical hyperalgesia to blunt and punctuated stimulation of the freeze lesion is predominantly caused by a peripheral mechanism.

Disposition and miotic effects of oral alfentanil: a potential noninvasive probe for first-pass cytochrome P4503A activity

BACKGROUND AND OBJECTIVES

Systemic clearance of the opioid alfentanil after intravenous administration is an excellent in vivo probe for hepatic cytochrome P4503A (CYP3A) activity and drug interactions. Alfentanil effect (miosis) is a surrogate for plasma alfentanil concentrations, and alfentanil effect kinetics may be a suitable noninvasive probe for hepatic CYP3A. Oral alfentanil might be a probe for first-pass CYP3A activity; however, it is not used clinically, and oral alfentanil disposition is unknown. This investigation evaluated the disposition and miotic effects of oral alfentanil.

METHODS

Ten healthy volunteers were studied in a dose-escalation fashion, receiving 23, 30, 43, and 75 microg/kg oral alfentanil on different days. Dark-adapted pupil diameter was measured at the time of venous blood sampling. Alfentanil was quantified by liquid chromatography-mass spectrometry. Plasma concentrations of alfentanil and pupil diameter change versus time data were analyzed by noncompartmental modeling.

RESULTS

Alfentanil was rapidly absorbed (time to maximum concentration [T(max)], 0.7 +/- 0.5 hour). Mean values for area under the plasma concentration-time curve extrapolated to infinity (AUC( infinity )) (27 +/- 14, 38 +/- 22, 57 +/- 31, and 105 +/- 59 ng x h x mL(-1)) and maximum concentration (16 +/- 8, 23 +/- 16, 31 +/- 18, and 50 +/- 22 ng/mL) were linear with dose, although there was considerable interindividual variability. T(max), elimination half-life (1.0 +/- 0.2 hours), total body clearance after oral administration (20 +/- 18 mL x kg(-1) x min(-1)), and dose-normalized AUC(infinity ) were independent of dose. Dose-dependent alfentanil disposition was mirrored by commensurate changes in clinical effect, although miosis was variable and not detectable in all subjects at the lowest dose. Mean miosis AUC (AUEC) and peak miosis were log-dose linear. Effect half-life (1.3 +/- 0.9 hours) was similar to plasma half-life.

CONCLUSION

Oral alfentanil is rapidly absorbed, exhibits linear and dose-independent kinetics, and undergoes substantial first-pass metabolism. Oral alfentanil may be a suitable probe for first-pass CYP3A activity. Alfentanil effect (miosis) may be an acceptable surrogate for plasma alfentanil concentrations. Oral alfentanil effect may be a noninvasive surrogate for conventional pharmacokinetics. Further studies are warranted to determine whether oral alfentanil and alfentanil effect kinetics may be a suitable noninvasive in vivo probe for first-pass CYP3A activity.

Plasma concentrations of morphine, morphine-6-glucuronide and morphine-3-glucuronide and their relationship with analgesia and side effects in patients with cancer-related pain

Morphine, the recommended drug for the management of moderate to severe cancer pain, is metabolized predominantly to the glucuronides morphine-6-glucuronide (M6G) and morphine-3-glucuronide (M3G). The quantitative clinical importance of these metabolites following the administration of oral morphine is unclear. This study investigates the relationship between plasma concentrations of morphine (M), M6G, M3G and clinical effects in patients receiving sustained release oral morphine for cancer-related pain. Peak and trough plasma concentrations of morphine and its metabolites were determined by high-performance liquid chromatography (HPLC). At corresponding time points, pain [Visual Analogue Scales (VAS), Verbal Rating Scales (VRS), Pain Relief Scores (PRS)] and toxicity (VAS and VRS) were assessed. Renal and liver function tests were performed. Forty-six patients were included in the study. There was a significant correlation between dose and both peak and trough plasma M, M6G and M3G (r > 0.60, P < 0.001 for each). Differences between peak and trough M, M6G, M3G, M+M6G, M6G:M, M3G:M and M3G:M6G were all significant (P < 0.001 for each). Pain was generally well controlled in the group, with a median VAS of 15 mm at the peak blood sampling time point. The differences between peak and trough values for VAS pain, VAS nausea and VAS drowsiness were not statistically significant (P = 0.078, 0.45 and 0.099, respectively). There were no differences in peak or trough morphine and metabolite concentrations or ratios between patients with low (< median) or high pain scores. Similarly, there was no significant relationship between high and low plasma concentrations and clinical effect. This study did not identify a simple relationship between plasma concentrations of morphine, morphine metabolites or metabolite ratios and clinical effects in patients with cancer and pain who were receiving chronic oral morphine therapy. Although overall pain control was good, there was marked interpatient variability in the dose of morphine and the plasma concentrations necessary to achieve this degree of analgesia.

Hydromorphone transfer into breast milk after intranasal administration

STUDY OBJECTIVES

To determine the distribution of hydromorphone into breast milk and the potential exposure of the suckling infant, and whether the distribution of hydromorphone into milk can be predicted accurately by a passive diffusion model.

DESIGN

Single-dose, pharmacokinetic study.

SETTING

University clinical research unit.

PATIENTS

Eight lactating, nonsmoking, healthy women aged 24-32 years.

INTERVENTION

Hydromorphone HCl 2 mg was given intranasally to the women to characterize its pharmacokinetics and extent of its transfer into breast milk.

MEASUREMENTS AND MAIN RESULTS

Plasma and milk samples were analyzed using liquid chromatography with tandem mass spectrometry detection. The milk:plasma ratio (M:P) was calculated as the total area under the concentration-time curve (AUC) of the milk divided by the total AUC of the plasma. Predicted in vitro M:P ratios were calculated using a diffusion model. Protein binding in milk and plasma, partitioning into milk fat (whole milk:skim milk ratios), as well as pH partitioning between plasma and milk were incorporated in the model. Protein binding was determined by equilibrium dialysis. Protein binding was minimal in both milk and plasma, with unbound fractions of 1 and 0.84, respectively There was little partitioning into milk fat, as demonstrated by the whole milk:skim milk ratio of 0.98. The observed and predicted M:P ratios +/- SD for hydromorphone were 2.57 +/- 0.47 and 1.11 +/- 0.28, respectively. The 95% confidence interval for the observed M:P ratio overlapped the confidence interval of the predicted M:P ratio, a finding that supports a role for both passive diffusion and active transport as mechanisms of hydromorphone transfer into milk.

CONCLUSION

Hydromorphone distributes rapidly from plasma into breast milk; however, the drug does not partition into fat. The suckling infant would receive approximately 0.67% of the maternal dose of hydromorphone (adjusted for body weight). As this is a limited exposure, further studies are needed to determine any potential impact to an infant who is fed breast milk from a mother treated with hydromorphone.

Postoperative analgesia in dogs receiving epidural morphine plus medetomidine

This investigation was carried out to compare the postoperative analgesia and plasma morphine concentrations in dogs given epidural morphine or epidural morphine combined with medetomidine prior to surgery. Twelve dogs (seven males and five females) with ruptured cranial cruciate ligaments presented to the Washington State University Veterinary Teaching Hospital. Six dogs received an epidural injection of morphine (0.1 mg/kg) and six dogs received epidural morphine (0.1 mg/kg) combined with medetomidine (0.005 mg/kg). Numeric rating scale (NRS) pain scores and cumulative pain scores (CPS) were assigned to 10-min segments of video. Video segments, heart rates and respiratory rates were recorded prior to premedication and at 4, 8, 12, 18 and 24 h after epidural injection. Blood was sampled from the cephalic vein at each of these times and during anesthesia at 0.5, 1, 2 and 3 h after epidural injection. Data were analyzed using either Friedman's test or one-way anova for repeated measures. In the morphine group, significant increases compared with premedication values were detected at 4, 8 and 12 h after epidural injection for NRS and at 4 and 12 h after epidural injection for CPS. In the morphine plus medetomidine group, NRS was significantly higher at 4 and 8 h whereas there were no differences from baseline values for CPS. Plasma morphine concentrations were not significantly different between treatment groups, but were significantly increased compared with preinjection values at 0.5, 1, 12, 18, and 24 h in the morphine plus medetomidine group. Epidurally administered morphine combined with medetomidine was associated with only minor benefits based on subjective pain scoring when compared with morphine alone in these dogs undergoing repair of a ruptured cranial cruciate ligament.

Predictive performance of computer-controlled infusion of remifentanil during propofol/remifentanil anaesthesia

BACKGROUND

The predictive performance of the available pharmacokinetic parameter sets for remifentanil, when used for target-controlled infusion (TCI) during total i.v. anaesthesia, has not been determined in a clinical setting. We studied the predictive performance of five parameter sets of remifentanil when used for TCI of remifentanil during propofol anaesthesia in surgical patients.

METHODS

Remifentanil concentration-time data that had been collected during a previous pharmacodynamic interaction study in 30 female patients (ASA physical status I, aged 20-65 yr) who received a TCI of remifentanil and propofol during lower abdominal surgery were used in this evaluation. The remifentanil concentrations predicted by the five parameter sets were calculated on the basis of the TCI device record of the infusion rate-time profile that had actually been administered to each individual. The individual and pooled bias [median performance error (MDPE)], inaccuracy [median absolute performance error (MDAPE)], divergence and wobble of the remifentanil TCI device were determined from the pooled and intrasubject performance errors.

RESULTS

A total of 444 remifentanil blood samples were analysed. Blood propofol and remifentanil concentrations ranged from 0.5 to 11 micro g ml(-1) and 0.1 to 19.6 ng ml(-1) respectively. Pooled MDPE and MDAPE of the remifentanil TCI device were -15 and 20% for the parameter set of Minto and colleagues (Anesthesiology 1997; 86: 10-23), 1 and 21%, -6 and 21%, and -6 and 19% for the three parameter sets described by Egan and colleagues (Anesthesiology 1996; 84: 821-33, Anesthesiology 1993; 79: 881-92, Anesthesiology 1998; 89: 562-73), and -24 and 30% for the parameter set described by Drover and Lemmens (Anesthesiology 1998; 89: 869-77).

CONCLUSIONS

Remifentanil can be administered by TCI with acceptable bias and inaccuracy. The three pharmacokinetic parameter sets described by Egan and colleagues resulted in the least bias and best accuracy.

Quantitative determination of piritramide in human serum applying liquid chromatography-two-stage mass spectrometry

A method for the determination of the synthetic narcotic analgesic piritramide in human serum utilizing high-performance liquid chromatography with atmospheric pressure chemical ionization two-stage mass spectrometry (HPLC-APCI-MS-MS) is presented. Pipamperone is used as the internal standard. Serum samples are prepared by liquid-liquid extraction under basic conditions with 1-chlorobutane. The chromatographic separation is achieved on an RP-18 stationary phase applying gradient elution with methanol-0.02% trifluoroacetic acid in water. Detection is carried out in the MS-MS single reaction monitoring mode of the ion-trap mass spectrometer. The limit of detection is 0.3 ng/ml and the calibration covers the range of 1-80 ng/ml. The intra-day RSDs are 6.1 to 7.3% over the calibration range, whereas the inter-day RSDs are 9.6 to 12.8%.

Simultaneous solid-phase extraction combined with liquid chromatography with ultraviolet absorbance detection for the determination of remifentanil and its metabolite in dog plasma

To establish pharmacokinetic/pharmacodynamic relationships, a selective and specific high-performance liquid chromatographic method was developed for the quantitation of remifentanil and its metabolite in dog plasma. The assay involves a solid-phase extraction and a reversed-phase chromatographic separation with ultraviolet detection (lambda=210 nm). The calibration curves are linear in the range of 7.89-1500 ng ml(-1). Intra-day assay variability is less than 7% for all standards evaluated. Good recovery, linearity, accuracy, and precision were achieved with the assay that proved readily applicable to pharmacokinetic studies in dogs.

Automated LC-MS Method for the Fast Stereoselective Determination of Methadone in Plasma

Methadone (MTD) is a chiral drug widely used for the treatment of opioid dependence for which a rapid analytical method for the determination of each enantiomer would be advantageous. In order to improve method sensitivity and to automate the entire analytical process, a column-switching configuration has been developed. An online extraction system coupled to a cellulose-based chiral stationary phase (CSP), namely Chiralcel OJ-R, was used and detection was performed by mass spectrometry. Fifty microl of plasma were injected into the liquid chromatography-mass spectrometry (LC-MS) system after addition of acetonitrile (ACN) containing methadone deuterated D9 (MTD-D9) (internal standard) and centrifugation. For the rapid extraction step, a large particle size support was selected. A baseline separation of MTD enantiomers was obtained in less than 12 min. Trueness and precision were evaluated with control samples at 500 ng/ml of (R,S)-methadone. Trueness values were 106.6% and 103.0% for (R)-MTD and (S)-MTD, respectively, with a coefficient of variation inferior to 2.5% for both compounds. Finally, a good concordance was found using this method for analysis of plasma samples from patients in maintenance treatment as compared to a previously described HPLC-UV method after liquid-liquid extraction.

Analgesic effects of morphine and morphine-6-glucuronide in a transcutaneous electrical pain model in healthy volunteers

OBJECTIVE

Our objective was to quantify the extent and time course of the effects of morphine-6-glucuronide and morphine on pain threshold, pain tolerance, pupil diameter, and side effects.

METHODS

In a double-blind, placebo-controlled, randomized, 3-way crossover study, 12 healthy volunteers (6 men and 6 women) received 63 to 112 mg of morphine-6-glucuronide or 26 to 66 mg of morphine as an intravenous bolus, followed by an infusion of the same medication for 1.8 to 6.4 hours. Analgesia was assessed every 30 minutes for up to 16 hours by means of transcutaneous electrical stimulation (sine wave, 5 Hz; intensity, 0-9.99 mA). Pupil diameter and side effects were recorded concomitantly.

RESULTS

At the administered doses, morphine-6-glucuronide and morphine had comparable effects on pain tolerance, pupil diameter, and side effects. The delay between the time course of the plasma concentrations and the time course of the effects was longer for morphine-6-glucuronide than for morphine (transfer half-life, 8.2 hours versus 2.6 hours for pain tolerance and 7.7 hours versus 2.8 hours for pupil diameter). The slope of the linear concentration versus effect relationship for pain tolerance was flatter for morphine-6-glucuronide than for morphine (0.05% versus 0.6% increase in pain tolerance per nanomole per liter of morphine-6-glucuronide and morphine at effect site, respectively). Morphine-6-glucuronide was less potent than morphine in producing pupil constriction (mean concentration at half-maximum effect, 745 nmol/L versus 26.4 nmol/L for morphine-6-glucuronide and morphine, respectively). In carriers of the mutated G118 allele of the mu-opioid receptor, the potency of the pupil-constricting effects of morphine-6-glucuronide and morphine was significantly smaller, and carriers of the G118 allele reported less nausea and vomited less often after administration of morphine-6-glucuronide.

CONCLUSIONS

Morphine-6-glucuronide clearly produced analgesic effects in healthy volunteers. However, the high amounts of systemic morphine-6-glucuronide needed to produce the same effects as morphine suggest that morphine-6-glucuronide barely contributes to the central nervous opioid effects after administration of analgesic doses of morphine.

Methadone maintenance treatment and St. John's Wort - a case report

St. John's wort, a popular over-the-counter drug for treatment of depression, might reduce concentrations of drugs such as cyclosporin and indinavir and lead to drug resistance and treatment failure. No studies as yet have examined its influence on methadone plasma levels. The trough methadone plasma levels were measured in four patients (2 males, median age: 31 years; range 19 - 40 years) in methadone maintenance treatment just before the introduction of St. John's wort (900 mg/d) and after a median period of 31-day treatment (range 14 - 47). The study was proposed to addict patients about to start an antidepressant therapy. Introduction of St. John's wort resulted in a strong reduction of (R,S)-methadone concentration-to-dose ratios in the four median patients included, with a median decrease to 47 % of the original concentration (range: 19 % - 60 % of the original concentration). Two patients reported symptoms that suggested a withdrawal syndrome. Thus, prescription of St. John's wort might decrease methadone blood levels and induce withdrawal symptoms which, if not correctly identified and handled (by changing the antidepressant or by increasing the methadone dose), might cause unnecessary discomfort to the patient, lead to resumption of illicit drug uses, or be a risk factor for discontinuation of the methadone or antidepressant treatment.

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.