The analgesic activity of morphine-6-glucuronide

Pharmacokinetics of morphine and its glucuronides after intravenous infusion of morphine and morphine-6-glucuronide in healthy volunteers

Steady-state pharmacokinetics of morphine and morphine-6-glucuronide (M-6-G) after intravenous administration of either morphine or M-6-G were determined in healthy volunteers. With a dosing regimen calculated on the basis of data obtained in a first series of experiments in four subjects (morphine: intravenous loading dose of 0.24 mg/kg for 5 minutes and an intravenous infusion of 0.069 mg.kg-1.hr-1 for 4 hours; M-6-G: loading dose of 0.011 mg/kg for 5 minutes and an infusion of 0.006 mg.kg-1.hr-1 for 4 hours), it was possible to yield plasma concentrations of morphine and M-6-G in another four subjects close to predefined targeted levels (35 and 45.5 ng/ml morphine and M-6-G, respectively). This dosing regimen may be used in further pharmacodynamic studies to compare the analgesic effects of morphine and M-6-G. In addition, metabolite kinetics of M-6-G were calculated as a function of time with use of a linear systems approach to the estimation of rate and fraction of morphine glucuronidation to M-6-G.

Evidence for P-glycoprotein-modulated penetration of morphine-6-glucuronide into brain capillary endothelium

1. Morphine-6-glucuronide is one of the major metabolites of morphine. The potent analgesic action of this compound together with its potential lower apparent toxicity in man, when compared with morphine, indicated its clinical importance. 2. Primary cultures of porcine brain capillary endothelial cells were used to study brain penetration of morphine-6-glucuronide. Biochemical characterization of the cell cultures revealed a marked enrichment in enzymatic activity of alkaline phosphatase (56 fold) and angiotensin converting enzyme (230 fold) as compared to whole brain tissue. By immunostaining the presence of vimentin, factor VIII, the tight junction associated protein ZO-1, and P-glycoprotein was shown. Functional characterization revealed that the carrier system responsible for transport of neutral amino acids was intact. 3. Uptake and transport of morphine-6-glucuronide was marginal and in the range of the extracellular marker sucrose. However, uptake of morphine-6-glucuronide was enhanced significantly (P < 0.0001) in presence of the inhibitors of P-glycoprotein, verapamil or vincristine. The finding that morphine-6-glucuronide may serve as a substrate for P-glycoprotein was confirmed in multidrug-resistant P388 tumour cells. 4. We conclude that penetration of the blood-brain barrier by morphine-6-glucuronide may depend on the expression of the product of the multidrug-resistance (MDR) gene in brain capillary endothelial cells.

Practical use of rectal medications in palliative care

The rectal route of drug administration is an efficient and economical method for pharmacologic intervention in the terminally ill patient for whom the oral route is precluded. This review first describes the physiology and general considerations surrounding rectal drug administration, then evaluates the literature pertaining to analgesic and adjuvant medications and dosage forms that are and are not approved for rectal administration by the U.S. Food and Drug Administration. A paucity of studies deal with rectal administration in terminally ill patients, and data have been gathered from pharmacokinetic studies or studies in which the drugs were used for other indications. Where plausible, practical clinical recommendations for the rectal use of opioids, nonopioid analgesics, anxiolytics, and other adjuvants are formulated.

Opioid analgesics: comparative features and prescribing guidelines

The term 'opioid' is a generic term for naturally occurring, semisynthetic and synthetic drugs which combine with opioid receptors to produce physiological effects and which are stereospecifically antagonised by naloxone. For clinical purposes, opioids can be classified according to their receptor interactions (agonist, partial agonist, agonist-antagonist and antagonist), the pain intensity for which they are conventionally used (moderate or severe), and their half-life (short or long). Pure agonists conventionally used for moderate pain, short and long half-life pure agonists conventionally used for severe pain, mixed agonist-antagonists and partial agonist opioids are described in detail. The effective clinical use of opioid drugs requires familiarity with drug selection, routes of administration, dosage guidelines and potential adverse effects. Opioids are unequivocally indicated in the management of severe acute pain and moderate to severe pain associated with cancer. There is increasing acceptance of the role of opioids in the management of recurring acute pain, chronic nonmalignant pain of organic origin and severe neuropathic pain. The selection of opioids is influenced by pain intensity, pharmacokinetic and formulary considerations, previous adverse effects and the presence of coexisting disease. Some patients will require sequential trials of several different opioids before a drug which is effective and well tolerated is identified. Opioid agents should be administered by the most comfortable and convenient route that meets the specific needs of the patient. The regimen for opioid medications should generally provide around-the-clock analgesia with provision for rescue doses for the management of exacerbations of the pain not covered by the regular dosage. At all times, uncontrolled pain should be addressed by gradual increase in the opioid dose until either pain control is achieved or intolerable and unmanageable adverse effects supervene. The management of pain with opioid analgesics demands frequent patient assessment and a readiness to re-evaluate the therapeutic plan in the setting of either inadequate relief or adverse effects.

Rectal administration of morphine in children. Pharmacokinetic evaluation after a single-dose

BACKGROUND

There is limited knowledge about the pharmacokinetics of morphine and its metabolites after rectal administration in children. In this study the pharmacokinetics of two different rectal formulations of morphine were examined and compared with intravenous morphine.

METHODS

Children undergoing elective surgery received rectal morphine 0.2 mg/kg before start of surgery. Ten children (mean age 14 months) received morphine rectally in a hydrogel formulation and another 10 children (mean age 16 months) received morphine rectally in a parenteral formulation. For comparison, 6 children (mean age 21 months) were given the same dose intravenously. The plasma concentrations of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) were measured by HPLC over 6 h after drug administration.

RESULTS

The mean rectal bioavailability of morphine was 35% (range 18-59) after hydrogel administration and 27% (range 6-93) after the solution. Mean values of Cmax were 76 nmol/l (25-129) and 56 nmol/1 (15-140), respectively. The results showed that morphine gel had a significantly higher bioavailability (P < 0.02) than the solution. The ratios of plasma (M3G + M6G) to morphine were higher after rectal administration (mean 7.5-8.7) than after i.v. injection (mean 5.3), indicating the presence of first-pass metabolism using the rectal route.

CONCLUSIONS

The rectal morphine hydrogel has pharmacokinetic properties which makes it a useful formulation for premedication and pain alleviation in paediatric patients.

A highly sensitive assay for the simultaneous determination of morphine, morphine-3-glucuronide, and morphine-6-glucuronide in human plasma by high-performance liquid chromatography with electrochemical and fluorescence detection

A novel, highly sensitive and specific bioanalytical method has been developed for the simultaneous determination of morphine and its major metabolites, morphine-3-glucuronide and morphine-6-glucuronide, in human plasma, using noroxymorphone as the internal standard. The analytes are isolated from human plasma using a nonpolar/polar C2 solid-phase extraction cartridge and analyzed by high-performance liquid chromatography with serial detection using electrochemical detection for morphine, morphine-6-glucuronide (M6G), and noroxymorphone and fluorescence detection for morphine-3-glucuronide (M3G). The limit of quantitation (sensitivity) using a 0.5-ml sample of plasma is 1 ng/ml, 10 ng/ml, and 5 ng/ml for morphine, M3G, and M6G, respectively. Standard curves were linear (correlation coefficients > 0.999) over the ranges 1-30 ng/ml, 10-500 ng/ml, and 5-100 ng/ml for morphine, M3G, and M6G, respectively. The overall interday accuracy of the method was -1.58% for morphine, 2.27% for M3G, and -5.34% for M6G. The assay is routinely used for the study of morphine, M3G, and M6G pharmacokinetics after oral administration of morphine.

Analgesic and immunomodulatory effects of codeine and codeine 6-glucuronide

PURPOSE

The antinociceptive and immunosuppressive effects of codeine and codeine 6-glucuronide were determined in rats after intracerebroventricular administration.

METHODS

Codeine 6-glucuronide was synthesized using a modification of the Koenigs-Knorr reaction. A lipophilic intermediate formed during synthesis, methyl [codein-6-yl-2,3,4-tri-O-acetyl-beta-D-glucopyranosid] uronate, was also tested. Morphine was used as a positive control to compare antinociceptive potencies of these compounds.

RESULTS

All compounds tested produced significant analgesic responses, as assessed by the tail flick model. Additionally, codeine 6-glucuronide showed significantly less immunosuppressive effects than codeine in vitro.

CONCLUSIONS

We conclude that codeine 6-glucuronide and related compounds may have clinical benefit in the treatment of pain in immune compromised patients.

Solid phase extraction of morphine and its metabolites from postmortem blood

A simple and rapid high-performance liquid chromatographic method is described for the determination of morphine-3-glucuronide, morphine-6-glucuronide, normorphine and morphine in postmortem blood. A solid phase extraction technique employing C18 Sep-Pak cartridges was used to recover morphine and its metabolites from 0.5 ml of blood. Reverse phase ion-pair chromatography was used to achieve separation with a C18 bonded column. The mobile phase consisted of acetonitrile, lauryl sulphate and sodium dihydrogen orthophosphate buffer at low pH. Electrochemical detection (ECD) in series with ultraviolet (UV) spectrophotometric detection (210 nm) was used for quantitation. The lower limit of detection using ECD was 10 ng/ml for all analytes and a linear response was observed to 5000 ng/ml. Coefficients of variation for all analytes ranged between 3-13% for both intra- and inter-assay. This method is reproducible, quick and easy to perform and allows morphine conjugates and morphine to be measured simultaneously in postmortem blood.

Rapid and highly automated determination of morphine and morphine glucuronides in plasma by on-line solid-phase extraction and column liquid chromatography

A high-performance liquid chromatography (HPLC) method has been developed for the determination of morphine and its main metabolites, morphine-6-glucuronide (M-6-G) and morphine-3-glucuronide (M-3-G), in plasma or cerebrospinal fluid. Samples were extracted using on-line solid-phase extraction followed by reversed-phase HPLC with fluorescence detection. Recoveries of 20 ng morphine and morphine glucuronides in plasma were over 95%. The limit of detection using 400 microliters of a biological matrix was 0.85, 3.4 and 1.0 ng/ml of M-3-G, M-6-G and morphine, respectively. Inter- and intra-day assay precision was better than 10%. The main advantages of the present described method are increased recoveries (> 95%) and a high degree of automation allowing a high speed in routine analysis. The time required for the fully automated analysis of one sample was less than 26 min.

Opioids: a pharmacologist's delight!

1. Opioids, in one form or another, have been used for their pain-relieving properties from prehistoric times: they are still the first line medication for the treatment of severe nociceptive pain and are likely to remain so for the foreseeable future. 2. The therapeutic index of opioids used for pain management is low: opioid side effects are essentially extensions of therapeutic effects and no available agent has a marked advantage over the others. When used for opioid 'anaesthesia', differences in therapeutic index are more obvious due to differences in non-opioid effects. 3. Opioid receptors in brain and spinal cord periphery are the main 'therapeutic targets' and clinical dosage strategies have been derived using a variety of systemic (indirect or blood-borne) methods as well as intraspinal and intracerebroventricular (direct) methods: no method, however, is without potential side effects. Peripheral opioid effects are now being exploited with intra-articular injection. 4. Opioid pharmacokinetics and pharmacodynamics are characterized by high inter-subject variability: accordingly, patient-controlled dosage strategies are found to be more successful for pain control than deterministic recipes.

Morphine and morphine metabolite concentrations in cerebrospinal fluid and plasma in cancer pain patients after slow-release oral morphine administration

In 34 cancer patients treated with chronic slow-release oral morphine, plasma and cerebrospinal fluid (CSF) minimum steady-state concentrations of morphine (M), morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) were determined by high-performance liquid chromatography (HPLC). Both plasma and CSF morphine, M3G and M6G, concentrations were linearly related to dose of morphine. At steady state, the mean +/- SEM CSF/plasma morphine concentration ratio was 0.8 +/- 0.1. In plasma and CSF, the mean steady-state concentrations of M3G and M6G substantially exceeded those of morphine where the mean CSF M/M3G/M6G ratio was 1:47:5 (weight basis), 1:34:4 (molar basis) and the mean plasma ratio was M/M3G/M6G 1:150:23 (weight basis), 1:109:17 (molar basis). The mean M3G and M6G concentrations in CSF at steady state were 15-18% of those found in plasma. Pain relief, evaluated by a visual analogue scale (VAS), did not correlate with the CSF M3G concentrations or with the M3G/M ratio. Since CSF M6G concentrations were high, M6G could, however, contribute to pain relief. We conclude that after oral administration of slow-release morphine, there is a significant passage of the morphine glucuronide metabolites to the CSF and that the M3G and M6G metabolites in CSF are in the concentration range where they may have an influence on analgesia.

Respiratory depression following morphine and morphine-6-glucuronide in normal subjects

1. Morphine 6-glucuronide (M6G) is a metabolite of morphine with analgesic activity. A double-blind, randomised comparison of the effects of morphine and M6G on respiratory function was carried out in 10 normal subjects after i.v. morphine (10 mg 70 kg-1) or M6G (1, 3.3 and 5 mg 70 kg-1). Analgesic potency was also assessed using an ischaemic pain test and other toxic effects were monitored. 2. Following morphine there was a significant increase in arterial PCO2, as measured by blood gases 45 min post dose (0.54 +/- 0.24 (s.d.) kPa, P < 0.001), and in transcutaneous PCO2 from 15 min post dose until the end of the study period (4 h), whereas blood gas and transcutaneous PCO2 were unchanged after M6G at 1.0, 3.3 and 5.0 mg 70 kg-1. This increased PCO2 following morphine was associated with an increase in expired CO2 concentration (FECO2) (0.20 +/- 0.14% expired air at 15 min post dose, P = 0.002), compared with small but significant reductions in FECO2 following morphine 6-glucuronide (-0.15 +/- 0.17% at 1 mg 70 kg-1 P = 0.030, -0.14 +/- 0.15% at 3.3 mg 70 kg-1 P = 0.017, -0.18 +/- 0.11% at 5 mg 70 kg-1 P = 0.024). Maximum transcutaneous PCO2 was significantly increased after morphine (0.63 +/- 0.28 kPa P = 0.009), but was not changed after M6G at 1 mg (0.10 +/- 0.34 kPa P = 0.11) 3.3 mg (0.06 +/- 0.37 kPa P = 0.34) or 5 mg (0.26 +/- 0.07 kPa P = 0.10).(ABSTRACT TRUNCATED AT 250 WORDS)

Biotransformation and pharmacokinetics of ethylmorphine after a single oral dose

1. The pharmacokinetics of ethylmorphine after administration of a single dose of the cough mixture Cosylan were investigated in 10 healthy subjects. 2. The median urinary recovery of ethylmorphine and measured metabolites was 77% over 48 h. The median tmax of unchanged ethylmorphine was 45 min, and the terminal elimination t1/2 was 2 h. Ethylmorphine-6-glucuronide was found to be the major metabolite. 3. Two subjects had significantly lower urinary recovery (0.48 h) of morphine and morphine-glucuronides than the remainder. Furthermore, these two had urinary metabolic ratios (MRO) and partial metabolic clearances (CLmO) for O-deethylation of ethylmorphine tentatively classifying them phenotypically as poor metabolisers of the debrisoquine/sparteine type. 4. Genotyping for cytochrome P450 (CYP) 2D6 alleles revealed five homozygote (wt/wt) and five heterozygote subjects. Two subjects phenotypically classified as poor metabolisers were genotypically CYP2D6A/wt and CYP2D6D/wt, respectively. 5. Serum and urine samples taken more than 8 and 24 h after administration of ethyl-morphine respectively, contained morphine and morphine-glucuronides, but no ethylmorphine, ethylmorphine-6-glucuronide or (serum only) norethylmorphine. Norethylmorphine could be detected after hydrolysis of urine samples in all subjects. The urinary recovery of the active metabolites morphine and morphine-6-glucuronide after administration of ethylmorphine varied by a factor of 9 between individuals. 6. The wide variation in recovery of morphine and morphine-glucuronides after oral administration of ethylmorphine could not be explained simply by a difference in CYP2D6 genotype. Constitutional variation in other enzymatic pathways involved in ethylmorphine metabolism is probably crucial. Ratios of morphine to parent drug cannot be used to distinguish the source of morphine after administration of ethylmorphine. Norethylmorphine should be included in urine assays for opiates in forensic toxicology, and no firm conclusions about the source of morphine are possible based on serum samples obtained more than 24 h after drug administration.

A specific radioimmunoassay for the determination of morphine-6-glucuronide in human plasma

A specific antiserum for morphine-6-glucuronide (M6G) has been raised in a rabbit in response to immunization with a novel hapten:protein conjugate (N-aminobutylnormorphine-6-glucuronide-thyroglobulin). Cross-reactivity with morphine and structurally related compounds was found to be negligible as expected from the nature of this immunogen. Using this antiserum, a simple, rapid and robust radioimmunoassay (RIA) has been developed for determination of M6G in samples of human plasma. The assay has a sensitivity of 0.05 ng/mL using 100 microL sample volumes and affords complete recovery of M6G over the range 2-200 ng/mL. The presence of morphine or morphine-3-glucuronide at concentrations up to 100 times the levels of M6G did not result in any measurable interference. Close agreement was obtained between M6G results obtained using the RIA and a specific high-performance liquid chromatography assay. This RIA offers an attractive alternative to existing methods for the determination of M6G in human plasma and will facilitate further metabolic and pharmacokinetic studies of morphine and M6G in the clinical setting.

The disposition of morphine and its metabolites in the in-situ rat isolated perfused liver

A specific HPLC method with UV detection was used to investigate the disposition of morphine and its metabolites in the in-situ rat isolated perfused liver preparation. Livers of male Sprague-Dawley rats (n = 4) were perfused under single pass conditions with protein- and erythrocyte-free perfusate, containing 2.66 microM morphine, for up to 90 min. The concentration of morphine, normorphine and morphine-3-glucuronide (M3G) in outflow perfusate, and the biliary excretion of M3G and normorphine glucuronide, all reached steady-state levels within 15-20 min after commencing perfusion. At steady-state, the mean (+/- s.d.) extraction ratio of morphine was 0.87 +/- 0.06 and clearance (26.0 +/- 1.7 mL min-1) approached perfusate flow rate (30 mL min-1). Although M3G was the main metabolite, accounting for 72.8 +/- 12.7% of eliminated morphine, a significant proportion (21.6 +/- 13.5%) was N-demethylated to normorphine and was recovered as unchanged normorphine in outflow perfusate and normorphine glucuronide in bile. The biliary extraction ratio of hepatically-formed M3G was 0.61 +/- 0.31. Results from an additional six experiments, in which livers were perfused with 1.33 and 2.66 microM of morphine for 30 min each in a balanced cross-over manner, indicated that the disposition of morphine and its metabolites was approximately linear within this concentration range.

Intravenous morphine pharmacokinetics in pediatric patients with sickle cell disease

To examine the pharmacokinetics of parenteral opioids, such as morphine, in patients with sickle cell disease, we determined the plasma morphine clearances in 18 patients (aged 6 to 19 years) who were receiving continuous intravenous infusions, and the pharmacokinetics of morphine in an additional six patients after single intravenous doses. Plasma morphine clearances ranged from 6.2 to 59.1 ml min-1 kg-1 (35.5 +/- 12.4, mean +/- SD) during steady-state infusions. There was a negative correlation between clearance values and age over the age range studied (p = 0.013). A significant difference (p = 0.042) was also observed in clearance values between patients who had serious adverse symptoms (23.4 +/- 10.7 ml min-1 kg-1) and those who had less serious symptoms (36.3 +/- 6.4 ml min-1 kg-1) when morphine was given at high dosage rates (> or = 0.15 mg kg-1 hr-1). Pharmacokinetic modeling of plasma morphine concentrations adequately fit a two-compartment model with a short initial distribution phase (mean half-life = 4.5 minutes) and a rapid terminal elimination half-life (77.6 +/- 19.2 minutes). These findings suggest that considerable individualization of morphine dosing may be necessary to achieve optimal analgesia and minimal adverse effects in these patients.

High-performance liquid chromatographic-electrospray mass spectrometric determination of morphine and its 3- and 6-glucuronides: application to pharmacokinetic studies

A rapid and selective assay of morphine and its 3- and 6-glucuronides in serum, based on high-performance liquid chromatography-electrospray mass spectrometry has been developed. The analytes and the internal standard, codeine or naltrexone, were subjected to solid-phase extraction, using ethyl solid-phase extraction columns, prior to chromatography. A reversed-phase column and a gradient mobile phase consisting of water and methanol were used. The mass spectrometer was operated in the selected-ion monitoring mode. The following ions were used: m/z 286 for morphine, m/z 300 for codeine, m/z 342 for naltrexone, and m/z 462 for morphine 3- and 6-glucuronides. The limit of quantitation observed with this method was 10 ng/ml morphine, 50 ng/ml morphine-6-glucuronide and 100 ng/ml morphine-3-glucuronide. The present method proved useful for the determination of serum levels of the parent drug and its metabolites in pain patients, heroin addicts and in morphine-treated mice.

Plasma and cerebrospinal fluid concentrations of morphine and morphine glucuronides in rabbits receiving single and repeated doses of morphine

The pharmacokinetics of morphine in plasma and the distribution of morphine and its glucuronidated metabolites within the cerebrospinal fluid were investigated in rabbits. After single morphine dosage, the plasma AUC ratio of morphine-3- glucuronide/morphine was 11.1 compared with 0.14 for morphine-6-glucuronide/morphine. The similar elimination half-lives of morphine (107 min), morphine-3-glucuronide (122 min), and morphine-6-glucuronide (105 min) suggested the glucuronidation to be the rate-limiting step, which was substantiated by the observation that morphine-3-glucuronide becomes eliminated four times faster when applied intravenously. Both after single and repeated morphine administration, the ratios of CSF and plasma levels of the parent drug were higher than those of morphine-3-glucuronide or morphine-6-glucuronide. These data demonstrate a poor penetration of the glucuronides across the blood-brain barrier and do not support the previously postulated accumulation of morphine-6-glucuronide in the central nervous system during chronic morphine treatment.

Affinity profiles of morphine, codeine, dihydrocodeine and their glucuronides at opioid receptor subtypes

The affinity of morphine, codeine, dihydrocodeine and their glucuronides for mu-, delta-, and kappa-opioid receptors was investigated. Binding was studied on guinea-pig brain homogenates with [3H]DAMGO, [3H]DPDPE, and [3H]U69593. The substitution of the free phenolic group of morphine caused a decrease in binding at opioid receptors without affecting the mu/delta-ratio nor that of mu/kappa. Glucuronidation of the 6-hydroxyl group of morphine, codeine or dihydrocodeine did not affect the affinity to mu-receptors, slightly increased the affinity for delta-receptors and reduced the affinity for kappa-receptors. The 6-glucuronides possess a decreased selectivity for mu-receptors over delta-receptors whereas that for mu- over kappa-receptors was increased. It is concluded that chemical variations at 3- and 6-position of morphine independently affect the affinity to opioid receptor subtypes.

Active hydroxymetabolites of antidepressants. Emphasis on E-10-hydroxy-nortriptyline

Hydroxymetabolites of the antidepressants nortriptyline and desipramine, like the parent drugs, inhibit neuronal uptake of noradrenaline (norepinephrine). In both plasma and cerebrospinal fluid (CSF), the concentrations of the 10-hydroxymetabolites of nortriptyline (10-OH-NT) are usually higher than those of the parent drugs, but there is a pronounced interindividual variation in the plasma concentrations. This shows that during treatment with nortriptyline, hydroxymetabolites exert, at least in some patients, major effects on brain noradrenaline neurons. Hydroxymetabolites of antidepressants are formed by the polymorphic cytochrome P450 enzyme CYP2D6. Nortriptyline is hydroxylated by this enzyme in a highly stereospecific way to the (-)-enantiomer of E-10-OH-NT. Among Caucasians, 7% are poor metabolisers of the CYP2D6 probe drug debrisoquine. These patients will form very little hydroxymetabolite. The affinity of E-10-OH-NT for muscarinic acetylcholine receptors in vitro was only one-eighteenth of the affinity of nortriptyline for these receptors. In healthy individuals, nortriptyline decreased saliva flow to a significantly greater extent than either E-10-OH-NT or placebo. In an ultrarapid hydroxylator of nortriptyline treated with very high doses of nortriptyline, the plasma concentration of unconjugated 10-OH-NT was very high without any sign of anticholinergic adverse effects. These results show that hydroxymetabolites of nortriptyline have much less anticholinergic effect than the parent drug. When racemic E-10-OH-NT per se was given to healthy individuals, the plasma concentration of the (-)-enantiomer was 5-fold higher than that of (+)-E-10-OH-NT. The 2 enantiomers were eliminated in parallel with an elimination half-life of 8 to 10 hours. A combined in vitro and in vivo investigation showed that a mean of 64% of (+)-E-10-OH-NT was glucuronidated in the liver and subsequently eliminated in urine. Of the administered (-)-enantiomer, a mean of 36% was eliminated as glucuronide formed in the intestine and 35% was actively secreted as unchanged form in urine. Plasma protein binding, determined by ultrafiltration, of the (+)- and (-)-enantiomers of E-10-OH-NT was 54 and 69%, respectively, which is less than that of nortriptyline (92%). The concentration of E-10-OH-NT in CSF was 50% of the concentration of unbound in plasma. There seems to be a stereoselective active transport of E-10-OH-NT from the CSF to blood. We administered racemic E-10-OH-NT to 5 patients during a major depressive episode.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential hemodynamic, metabolic and hormonal effects of morphine and morphine-6-glucuronide

Although the hyperglycemic effect of morphine has been previously described, it is not clear whether this is the result of increased glucose production and/or decreased glucose utilization and if this metabolic effect is lost with glucuronidation. This study assessed the hemodynamic (heart rate; HR and mean arterial blood pressure; MABP), hormonal and whole body glucose metabolic effects of morphine (MOR) and its metabolite morphine 6-glucuronide (MOR-6G) in conscious unrestrained chronically catheterized rats. Whole body glucose kinetics were assessed with a primed constant intravenous infusion of [3-3H]glucose in rats infused i.c.v. with H2O (Con; 5 microliters/h), MOR (80 micrograms/h) or MOR-6G (1 microgram/h) for a total of 4 h. MOR administration resulted in a significant 20% elevation in HR and no change in MABP. MOR-6G produced a 14% increase in HR and no change in MABP. A significant rise in plasma glucose (+23%), hepatic glucose production (Ra; +27-61%) and whole body glucose utilization (Rd; +31-61%) was also observed within 60 min of MOR administration. I.c.v. MOR-6G resulted in hyperglycemia (+60%), stimulation of glucose Ra (+60%) and glucose Rd (+50%). No significant alterations were noted in hemodynamic, metabolic and hormonal parameters of H2O infused rats. I.c.v. MOR resulted in a significant increases in epinephrine (2-fold), norepinephrine (50%), corticosterone (97%) with no alterations in plasma insulin and glucagon. I.c.v. MOR-6G resulted in more marked elevations in norepinephrine (5-fold), epinephrine (7-fold) and similar elevation in corticosterone (99%) and modest elevation of glucagon (40%).(ABSTRACT TRUNCATED AT 250 WORDS)

The dose-response relationship of controlled-release codeine (Codeine Contin) in chronic cancer pain

The improved pain control provided by regular dosing of opioid analgesics in patients with severe cancer pain has been well established. However, the treatment of mild-to-moderate cancer pain is often limited to "as needed" dosing with fixed combinations of codeine or oxycodone plus a nonopioid analgesic, which do not allow optimal titration of the individual components. This randomized double-blind study was designed to evaluate the efficacy of controlled-release codeine (Codeine Contin) in patients with cancer pain, and to estimate its dose equivalence to a standard combination of acetaminophen plus codeine. Twenty-four patients with at least moderate cancer pain were randomized to Codeine Contin 100, 200, or 300 mg every 12 hr or acetaminophen plus codeine (600 mg/60 mg) every 6 hr. On days 1 and 4 of dosing, pain intensity and pain relief were assessed hourly for 12 hr. The sum of pain intensity differences (SPID) from baseline and the total pain relief (TOTPAR) scores demonstrated a dose-response relationship for Codeine Contin on days 1 and 4 that was statistically significant on day 1 and suggested greater analgesic efficacy on day 4, compared with day 1. Codeine Contin 150 mg every 12 hr was estimated to be equianalgesic to acetaminophen plus codeine (600 mg/60 mg) given every 6 hr. Because a similar equivalence was also demonstrated from analysis of adverse event data, it is concluded that Codeine Contin 150 mg produces analgesia and a side-effect profile similar to a 40% lower dose of codeine provided by the combination.(ABSTRACT TRUNCATED AT 250 WORDS)

Palliative care

Though many of the treatment strategies used in palliative care have never been subjected to clinical trial, it has been argued that advances in palliative care have outstripped those in many other specialties. This article is not a comprehensive review of therapeutic options, nor even of recent advances in this topic, but concentrates on the latest developments and controversies in the pharmacological treatment of four frequent and important symptoms: neuropathic pain, anorexia and cachexia, intestinal obstruction, and breathlessness. It is difficult to perform blinded, randomised trials in patients with advanced disease and poor performance status, yet it is these patients who may gain most from the adoption of new well evaluated treatment strategies.

Evaluation of a differential radioimmunoassay technique for the determination of morphine and morphine-6-glucuronide in human plasma

A modified differential radioimmunoassay (RIA) technique for the measurement of morphine and its active metabolite, morphine-6-glucuronide (M6G), in plasma is described. Plasma samples were assayed following appropriate dilution, using a morphine specific antiserum and the results subtracted from those obtained with an antiserum which cross-reacts with both morphine and M6G. The sensitivity of measurement for morphine and M6G was 0.88 and 0.27 nmol l-1, respectively and inter-assay variation ranged from 3.4 to 11.0%. Recovery of morphine and M6G was quantitative over a range of concentrations (1-5000 nmol l-1). The presence of either M6G or morphine-3-glucuronide (M3G) did not affect the recovery of morphine. M6G was quantitatively recovered in the presence of morphine but high concentrations (> 1:20) of M3G caused some overestimation of M6G. Results obtained by differential RIA for both morphine and M6G correlated well with the results of HPLC analysis. The assay has been applied to the measurement of M6G in plasma following its administration to human volunteers.

Concentrations of morphine, morphine-6-glucuronide and morphine-3-glucuronide in serum and cerebrospinal fluid following morphine administration to patients with morphine-resistant pain

Recent studies have suggested that morphine-3-glucuronide (M3G) may antagonize the analgesic effects of morphine and morphine-6-glucuronide (M6G). To investigate this hypothesis, steady-state concentrations of morphine, M6G and M3G in serum and cerebrospinal fluid (CSF) were measured in 11 patients receiving chronic morphine therapy (9 orally and 2 subcutaneously) for treatment of cancer-related pain. All patients appeared to have morphine-resistant pain and had elected to proceed to intrathecal bupivacaine or percutaneous cordotomy. Morphine, M6G and M3G concentrations were measured by high-performance liquid chromatography. The concentrations (median and range) for morphine, M6G and M3G in serum were 193 (14-1086) nmol/l, 847 (210-4113) nmol/l and 4553 (1324-24035) nmol/l, respectively, while in CSF concentrations of morphine, M6G and M3G were 200 (21-1461) nmol/l, 115 (30-427) nmol/l and 719 (249-3252) nmol/l, respectively. Median molar ratios of M6G/morphine and M3G/morphine in serum were 3.79 and 22.1, respectively, while in CSF the same ratios were 0.42 and 2.39, respectively. Median molar ratios of M3G/M6G in serum and CSF were 5.84 and 6.61, respectively. The median molar ratios for CSF/serum distribution of morphine, M6G and M3G were 1.23, 0.12 and 0.14, respectively. Thus, despite their relatively poor ability to penetrate into the CSF, the high serum concentrations of M6G and M3G resulted in substantial concentrations of these metabolites in the CSF. Nevertheless, M3G/M6G ratios in our morphine-resistant patients were similar to published values in patients with well-controlled pain, suggesting that the hypothesis that M3G plays a major role in morphine-resistance is not correct.

Different biotransformation of morphine in isolated liver cells from guinea pig and rat

The biotransformation of morphine was characterized in freshly isolated parenchymal and non-parenchymal liver cells from rats and guinea pigs in suspension culture to establish an in vitro model for morphine metabolism. Liver cells were prepared by a collagenase perfusion technique, and separated by differential centrifugation. Morphine metabolism was investigated at different concentrations (1, 5, 100 and 200 microM). Samples were taken repeatedly during 2-4 hr of incubation, and subsequently analysed on a HPLC system employing both UV and electrochemical detection. In suspensions of hepatocytes from both animal species morphine-3-glucuronide (M3G) was the major metabolite of morphine, and was formed at comparable rates at all concentrations examined. Guinea pig hepatocytes in addition produced considerable quantities of morphine-6-glucuronide (M6G), whereas this metabolite was detected only intracellularly in minor quantities in rat hepatocytes. The ratio between the two morphine glucuronides (M3G/M6G) in suspensions of guinea pig hepatocytes was approximately 4:1. N-Demethylation of morphine was more pronounced per mg cell protein in rat hepatocytes compared to guinea pig cells. Metabolic activity towards morphine was not detected in non-parenchymal cells of the two species. The morphine glucuronidation pattern found in guinea pig hepatocytes resembles to a greater extent than that found in rat hepatocytes the pattern found in in vivo studies of humans. It was concluded that isolated guinea pig parenchymal cells appeared to be a promising in vitro system for studies of morphine glucuronidation, and to observe metabolism in general.

Effects of morphine metabolites on micturition in normal, unanaesthetized rats

1. By means of continuous cystometry in normal, unanaesthetized rats, the effects on micturition of intrathecally (i.t.) administered morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), the two main metabolites of morphine, were studied and compared with those of i.t. morphine. 2. Both M6G (0.01, 0.1, and 0.5 microgram) and M3G (5 micrograms) were found to have significant effects on micturition. Like morphine (0.1, 0.5, and 10 micrograms), M6G was able to inhibit the micturition reflex, and produce urinary retention and dribbling incontinence in a dose-dependent manner. The potency of M6G for inhibiting micturition was approximately 10 times higher than that of morphine, and the duration of its effect was longer. All effects of M6G could be reversed by naloxone. 3. M3G (5 micrograms) facilitated the micturition reflex, resulting in decreases in bladder capacity and micturition volume, and an increase in spontaneous contractile activity. Pretreatment with naloxone (10 micrograms), which by itself had no effect on micturition, enhanced the facilitatory effects of M3G. In addition, M3G tended to counteract the inhibitory effects of both morphine and M6G on micturition. M3G (5 micrograms) also produced an excitatory behavioural syndrome. 4. It is concluded that in rats, i.t. M3G has excitatory effects on micturition and behaviour, probably not mediated via opioid receptors. I.t M6G has a potent inhibitory effect on micturition mediated by stimulation of opioid receptors. It may have effects on somatosensory afferent input in lower doses than those required for effects on micturition.

Plasma concentrations and renal clearance of morphine, morphine-3-glucuronide and morphine-6-glucuronide in cancer patients receiving morphine

The plasma concentrations and renal clearance values of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) were determined in 11 adult cancer patients maintained on a long term oral morphine dosage (10 to 100mg every 4h). Concentrations in plasma and urine were determined by a specific high performance liquid chromatography assay. In this group of patients, whose creatinine clearance values ranged from 52 to 180 ml/min (3.12 to 10.8 L/h), average steady-state plasma concentrations of morphine, M3G and M6G were related (p < 0.01) to the morphine dose per kilogram of bodyweight. The mean total urinary recovery as morphine, M3G and M6G was 74.6 +/- 26.5% of the dose. Renal clearance values for M3G and M6G were closely related (r2 = 0.80; p < 0.0005). It was not possible to detect a relationship between the renal clearance of morphine, M3G and M6G, and that of creatinine. The renal tubular handling of all 3 compounds showed wide interindividual variation, and there was evidence of either net renal tubular secretion or reabsorption. There was no apparent relationship between plasma morphine and M6G concentrations and pain relief.