Determination of morphine, morphine-3-glucuronide and (tentatively) morphine-6-glucuronide in plasma and urine using ion-pair high-performance liquid chromatography

Comprehensive Characterization of Mouse UDP-Glucuronosyltransferase (Ugt) Belonging to the Ugt2b Subfamily: Identification of Ugt2b36 as the Predominant Isoform Involved in Morphine Glucuronidation

UDP-Glucuronosyltransferases (UGTs) are classified into three subfamilies in mice: Ugt1a, 2b, and 2a. In the Ugt1a subfamily, Ugt1a1 and 1a6 appear to correspond to human UGT1A1 and 1A6 The mouse is an important animal for its use in investigations, but the substrate specificities of Ugt isoforms belonging to the 2b subfamily in mice remain largely unknown. To address this issue, we characterized the substrate specificity of all isoforms of the Ugt2b subfamily expressed in the mouse liver. The cDNAs of Ugt1a1, Ugt2a3, and all the Ugt2b isoforms expressed in the liver were reverse-transcribed from the total RNA of male FVB-mouse livers and then amplified. A baculovirus-Sf9 cell system for expressing each Ugt was established. Of all the Ugts examined, Ugt2b34, 2b36, and 2b37 exhibited the ability to glucuronidate morphine with Ugt2b36, the most active in this regard. Ugt1a1, but also Ugt2b34, 2b36, and 2b37 to a lesser extent, preferentially catalyzed the glucuronidation of 17β-estradiol on the 3-hydroxyl group (E3G). With these isoforms, E3G formation by Ugt1a1 was efficient; however, Ugt2b5 exhibited a preference for the 17β-hydroxyl group (E17G). Ugt2b1 and Ugt2a3 formed comparable levels of E3G and E17G. Ugt2b1 and 2b5 were the only isoforms involved in chloramphenicol glucuronidation. As Ugt2b36 is highly expressed in the liver, it is most likely that Ugt2b36 is a major morphine Ugt in mouse liver. Regarding E3G formation, Ugt1a1, like the human homolog, seems to play an important role in the liver.

Alkaloid production and capacity for methyljasmonate induction by hairy roots of two species in Tribe Anthocercideae, family Solanaceae

In addition to producing medicinally important tropane alkaloids, some species in the mainly Australian Solanaceous tribe Anthocercideae, sister to genus Nicotiana, are known to also contain substantial levels of the pyridine alkaloids nicotine and nornicotine. Here, we demonstrate that axenic hairy root cultures of two tribe Anthocercideae species, Cyphanthera tasmanica Miers and Anthocercis ilicifolia ssp. ilicifolia Hook, contain considerable amounts of both nicotine and nornicotine (~0.5-1% DW), together with lower levels of the tropane alkaloid hyoscyamine (<0.2% DW). Treatment of growing hairy roots of both species with micromolar levels of the wound stress hormone methyl-jasmonate (MeJa) led to significant increases (P<0.05) in pyridine alkaloid concentrations but not of hyoscyamine. Consistent with previous studies involving Nicotiana species, we also observed that transcript levels of key genes required for pyridine alkaloid synthesis increased in hairy roots of both Anthocercideae species following MeJa treatment. We hypothesise that wound-associated induction of pyridine alkaloid synthesis in extant species of tribe Anthocercideae and genus Nicotiana was a feature of common ancestral stock that existed before the separation of both lineages ~15million years ago.

Detection of morphine-3-sulfate and morphine-6-sulfate in human urine and plasma, and formation in liver cytosol

Morphine is still the mainstay in treatment of severe pain and is metabolized in the liver mainly by glucuronidation, partly to the pharmacologically active morphine-6-glucuronide (M6G). The sulfation pathway has attracted much less attention but may also form active metabolites. The aim of the present study was to study two sulfate metabolites of morphine in humans. Urine and plasma from newborns, adult heroin addicts, and terminal cancer patients was analyzed for the presence of morphine-3-sulfate (M3S) and morphine-6-sulfate (M6S) by a new liquid chromatography – tandem mass spectrometry (LC-MS/MS) method. In addition, morphine sulfation was studied in vitro in human liver cytosol preparations. M3S was present in urine and plasma from all study groups although at lower concentrations than morphine-3-glucuronide (M3G). The plasma M3S/M3G ratio was 30 times higher in newborns than in adults indicating that the relative sulfation is more important at early stage of life. M6S was measurable in only one plasma sample from a newborn patient, and in one of the urine sample from the drug testing group. The incubation of morphine with liver cytosol extracts resulted in approximately equal rate of formation of both M3S and M6S. In conclusion, sulfation of morphine is catalyzed in human liver but this minor metabolic pathway probably lacks clinical significance. The M6S metabolite is formed at a low rate, making it undetectable in most individuals.

Influence of UGT2B7, OPRM1 and ABCB1 gene polymorphisms on postoperative morphine consumption

Therapeutic modulation of pain with morphine and other opioids is associated with significant variation in both effects and adverse effects in individual patients. Many factors including gene polymorphisms have been shown to contribute to the interindividual variability in the response to opioids. The aim of this study was to investigate the significance of UGT2B7, OPRM1 and ABCB1 polymorphisms for interindividual variability in morphine-induced analgesia in patients undergoing hysterectomy. The frequency of these polymorphisms was also investigated in forensic autopsies as morphine is also a very commonly abused drug. Blood samples were collected from 40 patients following abdominal hysterectomy, 24 hr after initiation of analgesia through a patient-controlled analgesia (PCA) pump. Samples were genotyped and analysed for morphine and its metabolites. We also genotyped approximately 200 autopsies found positive for morphine in routine forensic analysis. Patients homozygous for UGT2B7 802C needed significantly lower dose of morphine for pain relief. The same trend was observed for patients homozygous for ABCB1 1236T and 3435T, as well as to OPRM1 118A. The dose of morphine in patients included in this study was significantly related to variation in UGT2B7 T802C. Age was significantly related to both dose and concentration of morphine in blood. Regression analysis showed that 30% of differences in variation in morphine dose could be explained by SNPs in these genes. The genotype distribution was similar between the forensic cases and the patients. However, the mean concentration of morphine was higher in forensic cases compared to patients. We conclude that gene polymorphisms contribute significantly to the variation in morphine concentrations observed in individual patients.

Dispositional study of opioids in mice pretreated with sympathomimetic agents

Brain and plasma levels of morphine and codeine were determined by an assay method involving solid-phase extraction and ion-pair reversed phase HPLC. Detection was by a variable wavelength UV-detector (for codeine) and an amperometric electrochemical detector (for morphine) coupled in series. Ephedrine or phenylpropanolamine pretreatment did not interfere with the plasma disposition of morphine, evidenced by overlapping plasma concentration-time profiles. Brain opioid levels were equally unaffected by sympathomimetic pretreatment. The relative ratios of brain to plasma concentrations at the time corresponding to the respective peak anti-nociceptive activity for morphine and codeine revealed no significant differences. It is concluded that single doses of ephedrine and phenylpropanolamine do not affect the disposition of morphine and codeine in mice.

Morphine-3-glucuronide inhibits morphine induced, but enhances morphine-6-glucuronide induced locomotor activity in mice

The main metabolite of morphine, morphine-3-glucuronide (M3G) has no opioid effects. Some studies have rather indicated that it antagonizes the antinociceptive and respiratory depressive effects of both morphine and the active metabolite morphine-6-glucuronide (M6G). We studied the possible influence of M3G on the psychostimulant properties of morphine and M6G measured by locomotor activity. Mice were given two injections, one with either 80, 240 or 500 micromol/kg M3G or saline followed by an injection of 20 or 30 micromol/kg morphine or M6G. M3G influenced the locomotor activity induced by both morphine and M6G, but in opposite directions. M3G reduced the morphine induced locomotor activity during the first hour following morphine injection in a concentration dependent manner. M3G pretreatment did not significantly influence brain concentrations of morphine indicating that the interaction was of a pharmacodynamic type. In contrast M3G pretreatment increased the M6G induced locomotor activity. M3G pretreatment increased serum and brain M6G concentrations to an extent indicating that this interaction was mainly of a pharmacokinetic type. In conclusion our results disclose complicated interactions between morphine and its two metabolites with respect to induction of locomotor activity and possibly also with respect to mechanisms related to drug reward.

Morphine and its metabolites: Analytical methodologies for its determination

The present article reviews the methods of determination published for morphine and its metabolites covering the period from 1980 until at the first part of 2006. The overview includes the most relevant analytical determinations classified in the following two types: (1) non-chromatographic methods and (2) chromatographic methods.

Pharmacokinetic and Pharmacodynamic Evaluations of Novel Oral Morphine Sustained Release Granules

Pharmacokinetics and pharmacodynamics of novel oral sustained-release granules based on swelling polymer incorporation layer system (SPILA granules) containing morphine hydrochloride was evaluated. SPILA granules were designed to release morphine faster in neutral environment than in acidic one to keep higher plasma levels over a protracted period, especially after 12 h post dose. SPILA granules were orally administered to beagle dogs to compare the pharmacokinetics with commercially available twice-a-day dosage form, MS Contin. T(max) and AUC(0-24 h) values of SPILA granules were 6 h and 191 microg.h/ml, respectively. T(max) and AUC(0-24 h) values of MS Contin were 2 h and 146 microg.h/ml, respectively. Relative bioavailability following SPILA granules administration to twice-a-day MS Contin (30 mg) administration was 131%. In rats, analgesic effect was evaluated over 24 h. SPILA granules and aqueous solutions were administered to rats to compare the analgesic effect. AUC(0-24 h) value for SPILA granules was 8.88 microg.h/ml, which was a little lower than that for the aqueous solution (10.1 microg.h/ml), whereas the analgesic effect after SPILA granules once-a-day administration expressed as AURC (1701% Analgesia.h) was similar to that after the aqueous solution 4 times-a-day administration (1603% Analgesia.h). These results indicate that SPILA granules based on the pH-dependent release regulating polymer system can be a good candidate for an oral once-a-day sustained-release dosage form.

High-performance liquid chromatographic assay for morphine in small plasma samples: Application to pharmacokinetic studies in rats

In order to perform a reliable pharmacokinetic study of morphine during subchronic treatment in rats, an easy, rapid, sensitive and selective analytical method was proposed and validated. The analyte and internal standard (naloxone) were extracted from plasma samples (100 microL) by a single solid-phase extraction method prior to reverse-phase high performance liquid chromatography (HPLC) along with electrochemical detection (ED). Standard calibration graphs were linear within a range of 3.5-1,000 ng/mL (r=0.999). The intra-day coefficients of variation (CV) were in the range of 5.8-8.5% at eight concentration levels (7-1,000 ng/mL) and the inter-day coefficient of variation ranged from 7.4 to 8.8%. The intra-day assay accuracy was in the range of -5-10% and the inter-day assay accuracy ranged from 3.0 to 9.3% of relative error (RE). The limit of quantification was 3.5 ng/mL using a plasma sample of 100 microL (15.8% of CV and 12.8% of RE). Plasma samples were stable for 2 months at -20 degrees C. This method was found to be suitable for pharmacokinetic studies in rats, after subcutaneous administration of morphine (5.6 mg/kg per day) in subchronic treatment for 6 and 12 days.

Transport is not rate-limiting in morphine glucuronidation in the single-pass perfused rat liver preparation

Binding, transport, and metabolism are factors that influence morphine (M) removal in the rat liver. For M and the morphine 3beta-glucuronide metabolite (M3G), modest binding existed with 4% bovine serum albumin (unbound fractions of 0.89 +/- 0.07 and 0.98 +/- 0.09, respectively), and there was partitioning of M into red blood cells. Transport studies of M (<750 microM) showed similar, concentration-independent uptake clearances (CLs) of 1.5 ml min(-1) g(-1) among zonal and homogeneous, isolated rat hepatocytes. Transport of M3G, ascertained in multiple indicator dilution studies at various steady-state M3G concentrations (10-262 microM), uncovered a low and concentration-independent influx clearance (<10% of flow rate). The outflow dilution curve of [(3)H]M3G was superimposable onto that of [(14)C]sucrose, the extracellular reference, displaying similarity in transit times (23.5 and 22.2 s), negligible biliary excretion, and almost complete dose recovery from perfusate. In contrast, M3G occurred abundantly in both perfusate and bile in single-pass perfusion studies of the precursor, M, and revealed a biliary clearance of formed M3G that was 12.3-fold that of preformed M3G, suggesting a sinusoidal, diffusional barrier for M3G. With increasing concentrations of M (9-474 microM), clearance decreased, and metabolism and biliary excretion displayed concentration-dependent kinetics. Fitting of the data to a physiologically based liver model revealed that M removal mechanisms were saturable, with a K(m,met) of 52.2 microM and V(max,met) of 58.8 nmol min(-1) g(-1) for metabolism, and a K(m,ex) of 41.2 microM and V(max,ex) of 8.1 nmol min(-1) g(-1) for excretion. Sinusoidal transport was not rate-limiting for M removal.

Simple and sensitive determination of free and total morphine in human liver and kidney using gas chromatography-mass spectrometry

We developed a reliable, simple and sensitive method to determine free and total morphine in human liver and kidney, using gas chromatography-mass spectrometry (GC-MS). Free morphine or total morphine obtained by acid hydrolysis from 0.2g tissue sample was extracted using an Extrelut NT column with an internal standard, dihydrocodeine, followed by trimethylsilylation. The derivatized extract was submitted to GC-MS analysis of EI-SIM mode. The calibration curves of morphine in both liver and kidney samples were linear in the concentration range from 0.005 to 5 microg/g. The lower limits of detection of morphine were 0.005 microg/g. This method proved successful when we determined free and total morphine in liver and kidney obtained from an autopsied man who was mis-ingested morphine compound in the hospital, which resulted in the cause of death being morphine intoxication.

THE CONTRIBUTION OF FETAL METABOLISM TO THE DISPOSITION OF MORPHINE

The contribution of fetal metabolism to drug disposition in pregnancy is poorly understood. With maternal administration of morphine, like many drugs, steady-state concentrations in fetal plasma are less than in maternal plasma. The contribution of fetal metabolism to this difference is unknown. Morphine was used as a model drug to test the hypothesis that fetal metabolism contributes significantly to drug clearance by the fetus. Infusions of morphine, morphine-3-beta-glucuronide (M3G), and morphine-6-beta-glucuronide (M6G) were administered to the fetal baboon. Plasma concentrations of drug and metabolite obtained near steady state were measured by high-performance liquid chromatography. During morphine infusion, morphine, M3G, and M6G concentrations rose linearly with dose. M3G concentrations exceeded M6G by 20-fold. Mean +/- S.D. clearances of morphine, M3G, and M6G from the fetus were 69 +/- 17, 2.3 +/- 0.60, and 1.6 +/- 0.24 ml x min(-1), respectively. Clearances seemed to be dose-independent. The mean +/- S.D. fraction of morphine dose metabolized was 32 +/- 5.5%. This converts to a fetal metabolic clearance of 22 +/- 6.5 ml x min(-1). In conclusion, one third of the elimination of morphine from the fetal baboon is attributable to metabolism, one third to passive placental transfer, and one third undefined. Furthermore, there is no evidence for saturation of metabolism. Fetal metabolism is surprisingly high compared with in vitro estimates of metabolism and morphine clearance in human infants. For morphine, fetal drug metabolism accounts for half the difference between fetal and maternal plasma concentrations.

Determination of morphine, morphine-3-glucuronide and morphine-6-glucuronide in monkey and dog plasma by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry

A specific and simultaneous assay of morphine, morphine-3-glucuronide (M-3-G) and morphine-6-glucuronide (M-6-G) in monkey and dog plasma has been developed. These methods are based on rapid isolation using solid phase extraction cartridge, and high-performance liquid chromatography (HPLC)-electrospray ionization (ESI)-tandem mass spectrometric (MSMS) detection. Analytes were separated on a semi-micro ODS column in acetonitrile-formic (or acetic) acid mixed solution. The selected reaction monitoring for assay in monkey and dog plasma, as precursor-->product ion combinations of m/z 286-->286 for morphine, m/z 462-->286 for glucuronides and m/z 312-->312 for internal standard (IS, nalorphine) were used. The linearity of morphine, M-3-G and M-6-G was confirmed in the concentration range of 0.5-50, 25-2500, 2.5-250 ng/ml in monkey plasma, 0.5-100, 25-5000, 2.5-500 ng/ml in dog plasma, respectively. The precision of this assay method, expressed as CV, was less than 15% over the entire concentration range with adequate assay accuracy. Therefore, the HPLC-ESI-MSMS method is useful for the determination of morphine, M-3-G and M-6-G with sufficient sensitivity and specificity in pharmacokinetic studies.

The effect of blood sampling site and physicochemical characteristics of drugs on bioavailability after nasal administration in the sheep model

PURPOSE

Investigate the effect of blood sampling site and physicochemical characteristics of drugs on the pharmacokinetic (PK) parameters obtained after intravenous and nasal administration in sheep and compare results with computer simulations.

METHODS

Three drugs, insulin, morphine, and nicotine, were administered nasally and by intravenous (IV) injection to sheep, and serial blood samples collected concurrently from the carotid artery (insulin, morphine) or cephalic vein (nicotine) and jugular vein. Plasma drug concentrations were measured, and pharmacokinetic and statistical analyses performed, to evaluate sampling site differences.

RESULTS

After nasal insulin, bioavailabilities calculated from the two blood sampling site data were comparable. In contrast, apparent bioavailabilities following nasal morphine or nicotine were significantly higher when sampling was from the jugular vein. These results were supported by computer simulations. These observations are attributed to the greater effects of noninstantaneous mixing of drugs for jugular vein sampling following nasal dosing, compared to the other sampling sites, which is significant for drugs that are rapidly and well absorbed and that have a high volume of distribution (Vd).

CONCLUSION

The results clearly show that the characteristics of the drug and the blood sampling site can have a significant effect on the pharmacokinetic results obtained after nasal administration in sheep.

Discrepancies between ordered and delivered concentrations of opiate infusions in critical care

OBJECTIVES

We sought to test the assumption that the measured concentrations of medication infusions are within pharmaceutical standards (+/-10% of intended concentrations) and whether, at the time the infusion was mixed, the professional background of persons preparing the infusion or the unit for which the infusion was prepared were related to the observed variation.

DESIGN, SETTING, AND PARTICIPANTS

This prospective, observational study was conducted in the neonatal and pediatric intensive care units of a university-affiliated tertiary pediatric center. Morphine infusions prepared for clinical use were randomly sampled over a 7-month period. Those with no error between labeled and ordered concentration were further analyzed. High-performance liquid chromatography was used to determine the concentration of morphine infusions. The primary outcome was a difference of >10% between ordered and measured concentrations.

MEASUREMENTS AND MAIN RESULTS

The measured concentration of 65% of the 232 infusions was >10% different from the ordered concentration (95% confidence interval, 58-71%). The concentrations of 6% of infusions represented two-fold errors (95% confidence interval, 3-9%). The difference was normally distributed around zero, suggesting a cumulative effect of random errors, rather than a systematic bias. The time that the infusion was prepared, the professional background of the persons preparing the infusion, and the unit for which the infusion was mixed were not significant predictors of discrepancy (p =.74, analysis of variance).

CONCLUSIONS

The concentration of two thirds of infusions prepared for clinical use was outside accepted industry standards. These findings are likely to be broadly representative of intravenous drug administration in hospitalized children and pediatric pharmacokinetic studies. Further study of the causes and clinical impact is required.

Determination of heroin metabolites in human urine using capillary zone electrophoresis with β-cyclodextrin and UV detection

A method has been developed for the detection of a mixture of morphine, codeine, 6-acetyl morphine (6-AM) and normorphine using capillary zone electrophoresis (CZE). The method utilized urinary 6-AM as a diagnostic indicator of heroin abuse because it is not a product of either morphine or codeine metabolism. The electrophoretic separation was achieved using an uncoated (50 microm I.D.) fused-silica capillary, 77 cm long, containing the detector window 10.0 cm from the outlet end. The running buffer (pH 6.0) contained 50 mM sodium phosphate and 0.015 M beta-cyclodextrins (beta-CD). The samples were first extracted using a mixed-mode solid-phase extraction procedure and then analyzed by CZE. The UV absorbance detection was monitored at 214 nm. It has been found that beta-CDs can improve separation efficiency due to their hydrophobic cavity. The effect of the concentration of beta-CD and pH was also evaluated. The application of electrokinetic injection with field amplified sample stacking results in low detection limits (40 ng/ml for each analyte) and the method has good reproducibility, precision, accuracy, and high recovery.

Interpretation of the Presence of 6-Monoacetylmorphine in the Absence of Morphine-3-glucuronide in Urine Samples

The presence of morphine in a urinary sample may be caused not only by intake of heroin but also by intake of poppy-seed-containing food shortly before urine sampling or intake of drugs containing morphine, ethyl morphine, or codeine. To facilitate the interpretation, the heroin-specific metabolite 6-monoacetylmorphine (6-MAM) can be analyzed along with morphine-3-glucuronide (M3G) in an LC-MS verification analysis. In sporadic samples positive in the immunologic opiate screening test, 6-MAM, but not M3G, was found. To systematically analyze the finding all specimens with positive 6-MAM and/or M3G found during a 1-year period were investigated (n = 1923). Of these, 423 were positive for 6-MAM. In 32 (7.6%) of the samples 6-MAM was detected while the M3G concentrations were below cutoff (300 ng/mL) and in some cases even below the limit of detection (15 ng/mL). The 32 samples with this excretion pattern came from 13 different individuals, all but one with previously known heroin abuse. Eleven urine samples, nine containing M3G and 6-MAM and two with only 6-MAM, were also analyzed for the presence of heroin. In six samples, including the two with only 6-MAM, heroin was detected. There are several plausible explanations for these findings. The intake may have taken place shortly before urine sampling. High concentrations of heroin and 6-MAM may inhibit UGT 2B7, the enzyme responsible for glucuronidation of morphine. The hydrolyzation of 6-MAM to morphine may be disturbed by either internal or external causes. To elucidate this, further studies are required. Nevertheless, our finding demonstrates that routine measurement of 6-MAM when verifying opioid-positive immunologic screening results facilitates interpretation of low concentrations of M3G in urine specimens.

Pharmacokinetic differences of morphine and morphine-glucuronides are reflected in locomotor activity

The main metabolites of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), have been considered to participate in some of the effects of morphine. There is limited knowledge of the pharmacokinetics and dynamics of morphine and the main metabolites in mice, but mice are widely used to study both the analgesic effects and the psychomotor effects of morphine. The present study aimed to explore pharmacokinetic differences between morphine and morphine-glucuronides in mice after different routes of administration, and to investigate how possible differences were reflected in locomotor activity, a measure of psychostimulant properties. Mice were given morphine, M3G or M6G by different routes of administration. Serum concentrations versus time curves, pharmacokinetic parameters and locomotor activity were determined. Intraperitoneal administration of morphine reduced the bioavailability compared to intravenous and subcutaneous administration, but not so for morphine-glucuronides. The two morphine-glucuronides had similar pharmacokinetics, but morphine demonstrated higher volume of distribution and clearance than morphine-glucuronides. The present results demonstrated no locomotor effect of M3G, but a serum concentration effect relationship for morphine and M6G. When serum concentrations and effect changes were followed over time, there was some right hand shifts with respect to locomotor activity, especially during the declining phase of the concentration curve and particularly for M6G.

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.

Intranasal delivery of morphine

Morphine administered nasally to humans as a simple solution is only absorbed to a limited degree, with a bioavailability of the order of 10% compared with intravenous administration. This article describes the development of novel nasal morphine formulations based on chitosan, which, in the sheep model, provide a highly increased absorption with a 5- to 6-fold increase in bioavailability over simple morphine solutions. The chitosan-morphine nasal formulations have been tested in healthy volunteers in comparison with a slow i.v. infusion (over 30 min) of morphine. The results show that the nasal formulation was rapidly absorbed with a T(max) of 15 min or less and a bioavailability of nearly 60%. The shape of the plasma profile for nasal delivery of the chitosan-morphine formulation was similar to the one obtained for the slow i.v. administration of morphine. Furthermore, the metabolite profile obtained after the nasal administration of the chitosan-morphine nasal formulation was essentially identical to the one obtained for morphine administered by the intravenous route. The levels of both morphine-6-glucuronide and morphine-3-glucuronide were only about 25% of that found after oral administration of morphine. It is concluded that a properly designed nasal morphine formulation (such as one with chitosan) can result in a non-injectable opioid product capable of offering patients rapid and efficient pain relief.

Sex-specific differences in levels of morphine, morphine-3-glucuronide, and morphine antinociception in rats

A number of studies reported striking differences in antinociceptive responses to morphine as a function of sex. Although sex differences in the sensitivity to morphine are widely characterized in rodents, the underlying causes are not identified. Gonadal steroids are believed to contribute to sex differences in response to opioid-induced antinociception. In rats, morphine is metabolized by glucuronidation to morphine-3-glucuronide (M3G). M3G was found to be a functional antagonist of the actions of morphine. Knowledge about the role morphine glucuronides play in sex-specific responses to the antinociceptive effect of morphine may be useful in evaluating therapeutic outcomes of morphine treatment. The purpose of this project was to investigate the effects of sex on the systemic formation of M3G in rats and to correlate glucuronidation variability with differences in antinociceptive responses to morphine. Female rats showed significantly lower morphine-induced antinociception as compared to male rats; 4.6+/-0.5s vs. 11.7+/-2.2s, respectively. Female rats also demonstrated about three-fold higher maximum plasma levels of M3G compared with male rats; 6.2+/-2.2 microg/ml vs. 1.9+/-0.7 microg/ml, respectively. The M3G:morphine AUC ratio was 6.6:1 in female rats and 0.7:1 in male rats. Gonadectomy only partially eliminated sex differences in morphine antinociception and plasma levels of M3G. The results of this study demonstrate that sex and sex differences in the M3G:morphine plasma ratio may play a role in male-female differences observed in morphine antinociception.

LC determination of morphine and morphine glucuronides in human plasma by coulometric and UV detection

A reversed-phase high-performance liquid chromatographic method with coulometric and UV detection has been developed for the simultaneous determination of morphine, morphine-3-glucuronide and morphine-6-glucuronide. The separation was carried out by using a Supelcosil LC-8 DB reversed-phase column and 0.1 M potassium dihydrogen phosphate (pH 2.5)--acetonitrile--methanol (94:5:1 v/v) containing 4 mM pentanesulfonic acid as the mobile phase. The compounds were determined simultaneously by coulometry for morphine and with UV detection for morphine-3-glucuronide and morphine-6-glucuronide. Morphine, morphine glucuronides and the internal standard were extracted from human plasma using Bond-Elut C18 (1 ml) solid-phase extraction cartridges. In the case of coulometric detection, the detection limit was 0.5 ng/ml for morphine; in the case of UV detection the detection limit was 10 ng/ml for morphine-3-glucuronide and for morphine-6-glucuronide, too.

On the assessment of drug metabolism by assays of codeine and its main metabolites

Codeine and its main metabolites appear to have advantages for assessing drug metabolic phenotypes. The authors have further developed a high-performance liquid chromatography (HPLC) method for the quantification of codeine and six of its metabolites in urine. Quantification was performed by electrochemical detection for morphine, normorphine, morphine-6-glucuronide, and the internal standard 4-O-methyldopamine; and by ultraviolet detection for codeine, norcodeine, and morphine-3-glucuronide. The method had a detection limit of 2 nmol/L(-1) for morphine and normorphine, 4 nmol/L(-1) for morphine-6-glucuronide, 3 nmol/L for the internal standard, 20 nmol/L(-1) for morphine-3-glucuronide, and 60 nmol/L(-1) for codeine and norcodeine. The coefficients of variations were <9% for intraday and <10% for interday analyses. The recovery of codeine and its metabolites ranged from 55% (for morphine-3-glucuronide) to 90% (for codeine, norcodeine, morphine, and morphine-6-glucuronide). Eleven healthy volunteers were phenotyped for CYP2D6 using codeine as well as debrisoquine and dextromethorphan. Ten subjects were extensive metabolizers (EM) and one a poor metabolizer (PM) of codeine, debrisoquine, and dextromethorphan. Significant correlations between the metabolic ratios (MRs) of the different probe drugs were obtained (r2 > 0.95, p < 0.001). This HPLC method is simple, sensitive, accurate, and reproducible for assessing the CYP2D6 phenotype.

Intraarticular morphine after arthroscopic ACL reconstruction: a double-blind placebo-controlled study of 40 patients

We compared analgesic effects and pharmacokinetics of intraarticular versus intravenous administration of morphine after arthroscopic anterior cruciate ligament surgery. In a double-blind placebo-controlled study, 40 patients were randomly allocated to one of four treatment groups. Group I received 1 mg morphine intraarticularly and saline intravenously; group II received 5 mg morphine intraarticularly and saline intravenously; group III received 5 mg saline intraarticularly and morphine intravenously and group IV, the control group, received saline both intraarticularly and intravenously. The pain scores were significantly lower in groups I and II at 24 hours postoperatively than in group IV, and in group II during the rest of the postoperative period, as compared to groups III and IV. After intraarticular injection of 1 mg and 5 mg morphine, respectively, low concentrations of morphine-6-glucuronide (M6G) were found in the circulation, while morphine-3-glucuronide (M3G) appeared late after the injection in concentrations that considerably exceeded those of morphine in groups I and II. The analgesic effect of intraarticular morphine together with the low levels of morphine and morphine-6-glucuronide in plasma further strengthens the view that opioids have a peripheral mechanism of action.

High-performance liquid chromatographic determination of morphine and its 3- and 6-glucuronide metabolites by two-step solid-phase extraction

To provide more accurate measurement of morphine and its metabolites for a study of the genetic differences on morphine response, a method for the analysis of morphine and its metabolites is described which has the advantages of increased sensitivity and specificity by using a cleaner extraction. The new extraction method involves both the hydrophobic isolation on a carbon cartridge and ion-exchange isolation on ion-exchange resin which has not preliminary been described for morphine analysis. The combination of these two steps successfully purified drugs from human plasma with maximum removal of interfering substance comparing with a conventional C18 cartridge alone. The analytes are quantified by high-performance liquid chromatography on a reversed-phase C18 column employing a mobile phase consisting of 25% acetonitrile in 0.05 M phosphate buffer (pH 2.1), and 2.5 mM sodium dodecyl sulfate as the pairing ion with a combination of electrochemical and fluorometric detections. The recoveries for morphine (M), morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G) and hydromorphone after the SPE procedure were 86+/-7.1%, 82+/-6.9%, 79+/-6.0% and 85+/-6.0%, respectively. Limits of detection for this method are 0.1 ng/ml for M, and 0.18 ng/ml for M3G and M6G. Limits of quantitation were approximately 0.25 ng/ml for M, and 0.45 ng/ml for M3G and M6G. The present assay was applied to measure M, M3G and M6G content in human plasma to test the applicability and suitability of this method for clinical and research use.

Route-dependent metabolism of morphine in the vascularly perfused rat small intestine preparation

PURPOSE

1. To compare the disposition of tracer morphine ([3H]M) following systemic and intraduodenal administration in the recirculating, rat small intestine preparation in absence or presence of verapamil (V), an inhibitor of P-glycoprotein. 2. To develop a physiological model to explain the observations.

METHODS

A bolus dose of [3H]M was added to the reservoir or injected into the duodenum of the rat small intestine preparation. V (200 microM in reservoir) was either absent (control studies) or present. Intestinal microsomal, incubation studies were performed to evaluate the effect of V on morphine glucuronidation.

RESULTS

After systemic administration, [3H]M was not metabolized but was exsorbed into lumen. By contrast, both [3H]M and the 3beta-glucuronide metabolite, [3H]M3G, appeared in reservoir and lumen after intraduodenal administration. A physiologically-based model that encompassed absorption, metabolism and secretion was able to describe the route-dependent glucuronidation of M. The presence of V resulted in diminished levels of M3G in perfusate and lumen and mirrored the observation of decreased glucuronidation in microsomal incubations. Verapamil appeared to be an inhibitor of glucuronidation and not secretion of M.

CONCLUSIONS

M was secreted and absorbed by the rat small intestine. Route-dependent glucuronidation of M was explained by physiological modeling when M was poorly partitioned in intestinal tissue, with a low influx clearance from blood and a even poorer efflux clearance from tissue. The poor efflux rendered a much greater metabolism of M that was initially absorbed from the lumen. V increased the extent of M absorption through inhibition of M glucuronidation.

Method for quantification of morphine and its 3- and 6- glucuronides, codeine, codeine glucuronide and 6-monoacetylmorphine in human blood by liquid chromatography-electrospray mass spectrometry for routine analysis in forensic toxicology

Simultaneous determination of opiates and their glucuronides in body fluids has a great practical interest in the forensic assessment of heroin intoxication. A selective and sensitive method for quantification of morphine and its 3- and 6-glucuronides, codeine, codeine glucuronide and 6-monoacetylmorphine (6-MAM) based on liquid chromatography-electrospray ionisation mass spectrometry is described. The drugs were analysed in human autopsy whole blood after solid-phase extraction on a C8 cartridge. The separation was performed on an ODS column in acetonitrile (analysis time 15 min). For the quantitative analysis, deuterated analogues of each compound were used as internal standards. Selected-ion monitoring was applied where the molecular ion was chosen for quantification. The limits of quantification were 0.5 ng/ml for morphine and 6-MAM and 1 ng/ml for the 6-glucuronide of morphine, codeine-6-glucuronide and codeine and 5 ng/ml for the 3-glucuronide of morphine.

Comparison of analgesic efficacy of oxycodone and morphine in postoperative intravenous patient-controlled analgesia

BACKGROUND

Morphine has been the standard opioid in patient-controlled analgesia (PCA). Oxycodone, the analgesic potency of which in i.v. administration has been suggested to be slightly greater than that of morphine, has not yet been studied for its efficacy in PCA.

METHODS

Fifty patients, undergoing a plastic reconstruction of the breast or a major operation of the vertebrae, such as lumbar spinal fusion, used PCA for postoperative pain. Patients were randomized to receive either morphine 45 microg/kg or oxycodone 30 microg/kg as i.v. bolus doses. Patients were assessed for pain with a visual analogue scale (VAS) and side effects at 3, 9 and 24 h. Venous blood samples for the measurement of plasma concentration of oxycodone and that of morphine and its metabolites were taken.

RESULTS

In this study patients needed, on average, the same amount of oxycodone and morphine in the recovery room and on the ward. There was no difference in the quality of analgesia (VAS) or incidence of side effects, such as nausea, vomiting, pruritus and urinary retention. The plasma concentrations of morphine-6-glucuronide showed that this metabolite might contribute to the analgesia resulting from morphine administration.

CONCLUSIONS

The same dose of intravenous oxycodone and morphine administered by PCA pump was needed for immediate postoperative analgesia. The two drugs appear to be equipotent.

Near fatal intoxication with controlled-release morphine tablets in a depressed woman

BACKGROUND

A 46-year-old woman suffering from a reactive depression was admitted to the emergency room in coma and with severe respiratory failure. She later developed cardiovascular instability and general convulsions. Two days following admission the patient had no respiratory effort but was able to communicate in writing that she had ingested a large amount of controlled-release morphine tablets. Following treatment with naloxone she was successfully weaned from the respirator the next day.

METHODS

Sampling for determination of plasma and urine concentrations of morphine and its metabolites morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) was started 60 h after the presumed time of intake and continued up to 8 days after admission.

RESULTS

The initial plasma concentrations of morphine, M3G and M6G were 2160, 13100 and 2330 nM, respectively, compatible with a lethal dose in an opioid-naive patient. The urinary recovery of morphine, M3G and M6G corresponded to 6.8 mmol, equivalent to an oral intake of at least 2500 mg.

CONCLUSION

The plasma concentrations of morphine and morphine metabolites documented in this case, indicative of considerable absorption of drug, demonstrate that prolonged observation is necessary following intoxications with controlled-release morphine tablets. This case also highlights the importance of continuous follow-up of oral morphine therapy, so that unused drug is not left unaccounted for in the patient's home.

Simultaneous determination of codeine and its seven metabolites in plasma and urine by high-performance liquid chromatography with ultraviolet and electrochemical detection

A sensitive and selective high-performance liquid chromatography method has been developed for the measurement of codeine and its seven metabolites, norcodeine, morphine, normorphine, codeine-6-glucuronide, morphine-6-glucuronide, morphine-3-glucuronide and norcodeine glucuronide, in plasma and urine. The compounds were recovered from plasma and urine using solid-phase extraction with C18 cartridges and separated on a reversed-phase C8 column with a mobile phase consisting of 77% buffer (5 mM sodium phosphate monobasic and 0.70 mM sodium dodecyl sulfate, pH 2.35) and 23% acetonitrile. Codeine, norcodeine, codeine-6-glucuronide, norcodeine glucuronide and morphine-3-glucuronide were detected by ultraviolet detection at 214 nm, with a detection limit of 0.02 nmol/ml for each compound in plasma. Morphine-6-glucuronide, normorphine and morphine were monitored by electrochemical detection at 350 mV, with a detection limit of 0.003 nmol/ml for each compound in plasma. The assay showed good reproducibility and accuracy using external standardization. The recovery and inter-day variation for all compounds in plasma samples were 63.40-77.90% and 3.49-16.77% (R.S.D.) and while in urine were 64.98-90.13% and 2.93-9.96% (R.S.D.), respectively.

High-performance liquid chromatography-mass spectrometry-mass spectrometry analysis of morphine and morphine metabolites and its application to a pharmacokinetic study in male Sprague-Dawley rats

A high-performance liquid chromatography tandem mass spectrometry-mass spectrometry (LC-MS-MS) assay was developed for the analyses of morphine, morphine glucuronides and normorphine in plasma samples from rats. The analytes were extracted by using C2 solid-phase extraction cartridges. The extraction recoveries were 100% for morphine, 84% for morphine-3-glucuronide, 64% for morphine-6-glucuronide and 88% for normorphine. Both intra- and inter-assay variabilities were below 11%. Using a plasma sample size of 100 microliters, the limits of detection were 13 nmol l-1 (3.8 ng ml-1) for morphine, 12 nmol l-1 (5.5 ng ml-1) for morphine-3-glucuronide, 26 nmol l-1 (12 ng ml-1) for morphine-6-glucuronide and 18 nmol l-1 (5.0 ng ml-1) for normorphine, at a signal-to-noise ratio of 3. The present assay was applied to a pharmacokinetic study in rats after intraperitoneal administration of morphine.

A universal radiochemical high-performance liquid chromatographic assay for the determination of UDP-glucuronosyltransferase activity

A new unified assay for the determination of UDP-glucuronosyltransferase (UGT) activities has been developed. The resolution of [14C]uridine diphosphate glucuronic acid from radiolabeled glucuronides formed by incorporation of this radiolabel can now be achieved by a sensitive and rapid-gradient HPLC method which utilizes a radioactivity endpoint as a universal detection method. One important application of this method is the determination of kinetic parameters for cloned and expressed UGT isoforms with greater speed and precision than can be afforded by TLC methodology. Moreover, assays with 14C-labeled substrates indicate that gradient HPLC can easily resolve the substrate from the glucuronide products and present an alternative to the time-consuming optimization of conditions for organic phase extraction assays.

Does prolonged oral treatment with sustained-release morphine tablets influence immune function?

Opioids such as morphine are the mainstay of acute and chronic pain treatment. The purpose of this study was to investigate the immunosuppressive effects of morphine in patients with pain syndromes. We investigated 10 patients with chronic pain syndromes undergoing treatment with oral sustained-release morphine (30-240 mg/d) before and after 1,4, and 12 wk of treatment compared with healthy control subjects without morphine treatment. Immunological variables of the cellular and humoral immune axis showed that 1) total lymphocyte counts and the distribution of lymphocyte subpopulations, including helper T-cell/suppressor cytotoxic T-cell ratios (CD4/CD8 ratios), did not change compared with baseline or healthy control subjects; 2) proliferation of peripheral mononuclear cells (PMC) was not impaired by morphine treatment; 3) interleukin 2 production increased after 4 wk of treatment with morphine; and 4) immunoglobulin (Ig) production was reduced before initiation of therapy in pain patients and decreased further during morphine treatment, whereas Ig concentrations in the circulation remained at normal levels. These results indicate that treatment with oral, sustained-release morphine does not have a suppressive effect on overall PMC function. On the other hand, Ig production was impaired in patients with chronic pain and was further suppressed by morphine. Whether this suppression of humoral immune function has a clinical impact on the immune system as a whole remains to be determined.

IMPLICATIONS

Treatment of patients with chronic pain with oral, sustained-release morphine does not influence cellular immune function, but it suppresses the already attenuated production of immunoglobulins.

Determination of morphine and its 3- and 6-glucuronides, codeine, codeine-glucuronide and 6-monoacetylmorphine in body fluids by liquid chromatography atmospheric pressure chemical ionization mass spectrometry

A selective assay of morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G), morphine, codeine, codeine-6-glucuronide (C6G) and 6-monoacetylmorphine (6-MAM) based on liquid chromatography atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS) is described. The drugs were extracted from serum, autopsy blood, urine, cerebrospinal fluid or vitreous humor using C18 solid-phase extraction cartridges and subjected to LC-APCI-MS analysis. The separation was performed on an ODS column in acetonitrile-50 mM ammonium formate buffer, pH 3.0 (5:95), using a flow-rate gradient from 0.6 to 1.1 ml/min (total analysis time was 17 min). The quantitative analysis was done using deuterated analogues of each compound. Selected-ion monitoring detection was applied: m/z 286 (for morphine, M3G-aglycone and M6G-aglycone), 289 (for morphine-d3, M3G-d3-aglycone and M6G-d3-aglycone), 300 (for codeine and C6G-aglycone), 303 (for C6G-d3-aglycone), 306 (for codeine-d6), 328 (for 6-MAM), 334 (for 6-MAM-d6), 462 (for M3G and M6G), 465 (for M3G-d3 and M6G-d3), 476 (for C6G) and 479 (for C6G-d3). The limits of quantitation were: 1 microg/l for morphine, 2 microg/l for 6-MAM, 5 microg/l for M3G, M6G and codeine and 200 microg/I for C6G. The recovery ranged from 85 to 98% for each analyte. The method appeared very selective and may be used for the routine determination of opiates in body fluids of heroin abusers and patients treated with opiates.

Decreased patient analgesic requirements after liver transplantation and associated neuropeptide levels

BACKGROUND

Decreased morphine requirements have been reported after liver transplantation when compared with other types of major abdominal surgery. The aim of this study was to examine plasma concentrations of three neuropeptides involved in pain modulation-metenkephalin (ME), beta-endorphin (BE), and substance P (SP)-in patients undergoing orthotopic liver transplantation (OLT) and in control patients undergoing other liver operations. We then compared the postoperative analgesic requirements in these two groups of patients.

METHODS

Plasma levels of ME, BE, and SP were measured by radioimmunoassay at preincision, preemergence, and for 3 days after operation in 13 patients undergoing OLT and in 10 control patients. Patient-controlled analgesia morphine delivery was recorded for all patients postoperatively, and plasma morphine, its metabolites, and patient pain and sedation scores were also measured.

RESULTS

ME levels were elevated in all OLT patient samples when compared with control patient samples. BE levels were not significantly different at any time. SP levels were significantly decreased only in preincision and preemergence OLT patient samples. Total patient-controlled analgesia morphine delivered during the first 3 postoperative days was significantly less in OLT patients (70+/-8 mg) than in control patients (101+/-12 mg). Plasma morphine, morphine-3-glucuronide, and morphine-6-glucuronide levels were decreased in OLT patients, however, statistical significance was seen only in the morphine-6-glucuronide results.

CONCLUSIONS

We have shown that postoperative analgesic requirements are decreased in OLT patients, and we suggest that associated increased peripheral ME levels may be contributing to this decreased requirement. Based on our results, circulating BE and SP are less significant factors affecting postoperative analgesic requirements.

Highly sensitive gas chromatographic-mass spectrometric method for morphine determination in plasma that is suitable for pharmacokinetic studies

A sensitive method was devised to determine morphine plasma concentrations by gas chromatography-mass spectrometry (GC-MS) using selected ion monitoring (SIM) with nalorphine as the internal standard. This method was rugged, reliable, selective and sensitive and was used to determine the morphine content of over 2000 samples. Sample preparation involved extraction of basified sample using n-butyl chloride-chloroform (5:1) and evaporation of the extract to dryness. The residue was derivatised with pentafluoropropionic anhydride, evaporated to dryness, reconstituted in 40 microl toluene and injected onto the GC-MS. For a sample size of 1 ml, the limit of quantitation was 0.75 ng/ml (S/N ratio 10:1) and the estimated limit of detection was calculated to be 0.2 ng/ml (S/N ratio 3:1), expressed as morphine base. Precision (n=5) was 4.9% at 0.75 ng/ml, 6.8% at 1.5 ng/ml, 3.0% at 37.5 ng/ml and 2.3% at 150 ng/ml. Standard curves for the range of 0-750 ng/ml morphine in plasma were linear with all r2 values greater than 0.99. No interfering peaks were seen for either morphine or internal standard in the blank samples. The method is suitable for pharmacokinetic studies after subclinical doses of morphine where it has been used to study morphine plasma concentrations for 6 h after a dose of only 2 mg.