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

Morphine and hydromorphone pharmacokinetics in human volunteers: population-based modelling of interindividual and opioid-related variability

BACKGROUND

Morphine and hydromorphone have differing onsets, magnitudes, and durations of effects and side-effects. Differences between opioids in their interindividual variabilities in pharmacokinetics and pharmacodynamics might influence rational drug selection. Crossover drug studies can provide more informative interindividual variability data than parallel group studies. Using data from a crossover study of i.v. morphine and hydromorphone in healthy volunteers, we tested the hypothesis that morphine and hydromorphone differ in their interindividual pharmacokinetic variability.

METHODS

Arterial opioid and metabolite concentrations from a randomised crossover study in 51 volunteers receiving a 2-h infusion of hydromorphone (0.05 or 0.1 mg kg-1 i.v.) or morphine (total 0.1 or 0.2 mg kg-1 i.v.) 1-2 weeks apart were evaluated with a three-compartmental model for parent opioid and incorporating glucuronides using population modelling (NONMEM). The primary outcome was interindividual variability in pharmacokinetics, based on the coefficient of variation (%CV) of individual model parameters, calculated as √[exp(ω2)-1]×100 where ω2 is the interindividual variability.

RESULTS

Data were analysed per drug and in a combined morphine-hydromorphone model. Both analyses indicate that interindividual variabilities for hydromorphone and morphine were comparable with %CV ranging from 9% to 31% for structural model parameters (combined analysis). Similarly, additive and relative residual errors had comparable variabilities, 20-40% and 72-87%, respectively, for morphine and hydromorphone (combined analysis).

CONCLUSIONS

Morphine and hydromorphone did not differ in a statistically significant or clinically meaningful manner in their interindividual pharmacokinetic variability. Interindividual pharmacokinetic variability does not appear a meaningful consideration in the choice between these two opioids.

Revision of Pharmacological Treatment Recommendations for Cancer Pain: Clinical Guidelines from the Japanese Society of Palliative Medicine

Background: Pain is one of the most common symptoms in cancer patients. The Japanese Society for Palliative Medicine (JSPM) first published its clinical guidelines for the management of cancer pain in 2010. Since then, more research on cancer pain management has been reported, and new drugs have become available in Japan. Thus, the JSPM has now revised the clinical guidelines using a validated methodology. Methods: This guideline was developed through a systematic review, discussion, and the Delphi method, following a formal guideline development process. Results: Thirty-five recommendations were created: 19 for the pharmacological management of cancer pain, 6 for the management of opioid-induced adverse effects, and 10 for pharmacological treatment procedures. Due to the lack of evidence that directly addressed our clinical questions, most of the recommendations had to be based on consensus among committee members and other guidelines. Discussion: It is critical to continue to build high-quality evidence in cancer pain management, and revise these guidelines accordingly.

Bridging the gap between in silico and in vivo by modeling opioid disposition in a kidney proximal tubule microphysiological system

Opioid overdose, dependence, and addiction are a major public health crisis. Patients with chronic kidney disease (CKD) are at high risk of opioid overdose, therefore novel methods that provide accurate prediction of renal clearance (CL_r) and systemic disposition of opioids in CKD patients can facilitate the optimization of therapeutic regimens. The present study aimed to predict renal clearance and systemic disposition of morphine and its active metabolite morphine-6-glucuronide (M6G) in CKD patients using a vascularized human proximal tubule microphysiological system (VPT-MPS) coupled with a parent-metabolite full body physiologically-based pharmacokinetic (PBPK) model. The VPT-MPS, populated with a human umbilical vein endothelial cell (HUVEC) channel and an adjacent human primary proximal tubular epithelial cells (PTEC) channel, successfully demonstrated secretory transport of morphine and M6G from the HUVEC channel into the PTEC channel. The in vitro data generated by VPT-MPS were incorporated into a mechanistic kidney model and parent-metabolite full body PBPK model to predict CL_r and systemic disposition of morphine and M6G, resulting in successful prediction of CL_r and the plasma concentration–time profiles in both healthy subjects and CKD patients. A microphysiological system together with mathematical modeling successfully predicted renal clearance and systemic disposition of opioids in CKD patients and healthy subjects.

Opioid Management in Older Adults with Chronic Kidney Disease: A Review

Chronic pain, a common comorbidity of chronic kidney disease, is consistently under-recognized and difficult to treat in older adults with nondialysis chronic kidney disease. Given the decreased kidney function associated with aging and chronic kidney disease, these patients are at increased risk for drug accumulation and adverse events. Emerging research has demonstrated the efficacy of opioids in chronic kidney disease patients, but research specifically focusing on older, nondialysis chronic kidney disease patients is scarce. The primary objective of this review is to determine which oral and transdermal opioids are the safest for older, nondialysis chronic kidney disease patients. We discuss the limited existing evidence on opioid prescription in older, nondialysis chronic kidney disease patients and provide recommendations for the management of oral and transdermal opioids in this patient population. Specifically, transdermal buprenorphine, transdermal fentanyl, and oral hydromorphone are the most tolerable opioids in these patients; hydrocodone, oxycodone, and methadone are useful but require careful monitoring; and tramadol, codeine, morphine, and meperidine should be avoided due to risk of accumulation and adverse events. Because older adults with nondialysis chronic kidney disease are at increased risk for adverse events, vigilant monitoring of opioid prescription is critical. Lastly, collaboration among an interprofessional clinical team can ensure safe prescription of opioids in older adults with nondialysis chronic kidney disease.

Integrated Model to Describe Morphine Pharmacokinetics in Humans

The pharmacokinetics (PK) of morphine has been extensively investigated. Though different publications have focused on the various aspects of morphine PK, none have quantitatively interpreted morphine PK across different publications. The objective of this research is to summarize the current understanding of morphine PK in humans quantitatively. In this research, a parent-metabolite compartmental PK modeling approach was used to summarize the current understanding of morphine PK in humans. Plasma concentration-time profiles and cumulative urine recovery time profiles of morphine, morphine-3-glucuronide, and morphine-6-glucuronide were digitized from the previous publications to develop the parent-metabolite PK model. The parent-metabolite PK model successfully described the plasma concentration-time profiles and cumulative urine recovery of morphine as well as its two major metabolites, morphine-3-glucuronide and morphine-6-glucuronide, after intravenous and oral administration of morphine. This research separated out the first-pass effect on morphine metabolism after oral administration. By integrating these results with two mass balance studies of morphine, a clear picture of morphine absorption and disposition is given. Though the results are mainly based on data collected from healthy volunteers or patients whose disease is not expected to impact morphine PK, the parent-metabolite model sets a framework to further evaluate morphine PK in special populations, such as pediatrics and patients with renal impairment.

A Prospective Population Pharmacokinetic Study on Morphine Metabolism in Cancer Patients

Background

Oral and subcutaneous morphine is widely used for the treatment of cancer-related pain; however, solid pharmacokinetic data on this practice are lacking. Furthermore, it is largely unknown which factors contribute to the variability in clearances of morphine and its metabolites and whether morphine clearance is related to treatment outcome.

Methods

Blood samples from 49 cancer patients treated with oral and/or subcutaneous morphine were prospectively collected and were used to develop a population pharmacokinetic model for morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). The influence of age, gender, renal function and several polymorphisms possibly related to the pharmacokinetics of the three compounds was investigated. In addition, the relation between treatment failure and morphine and metabolite clearances was explored.

Results

A one-compartment model including an extensive first-pass effect adequately described the data of morphine and its metabolites. Estimated mean area under the plasma concentration–time curve (AUC) ratios following oral versus subcutaneous administration were: M3G/morphine 29.7:1 vs. 11.1:1; M6G/morphine 5.26:1 vs. 1.95:1; and M3G/M6G 5.65:1 vs. 5.70:1. Renal function was significantly correlated with clearance of the metabolites, which increased 0.602 L/h per every 10 mL/min/1.73 m² increase of estimated glomerular filtration rate (eGFR), reaching a plateau for eGFR >90 mL/min/1.73 m². The clearance of morphine or its metabolites was not found to be correlated with treatment failure.

Conclusion

The influence of age-, gender- and pharmacokinetic-related polymorphisms was not identified on the pharmacokinetics of morphine. Clearance of morphine or its metabolites was not found to explain treatment outcome; however, large variations in plasma concentrations of morphine, M3G and M6G support further studies on the relation between plasma concentrations and treatment outcome.

Dutch Trial Register ID: NTR4369.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-016-0471-7) contains supplementary material, which is available to authorized users.

Population Pharmacokinetics of Morphine in Patients With Nonalcoholic Steatohepatitis (NASH) and Healthy Adults

Altered expression and function of transporters in nonalcoholic steatohepatitis (NASH) patients may affect the pharmacokinetics (PK), efficacy, and safety of substrate drugs. A population pharmacokinetic (PopPK) analysis was performed to assess differences in morphine and morphine-3-glucuronide (M3G) disposition in NASH and healthy subjects. A total of 315 serum and 42 urine samples from 21 subjects (14 healthy; 7 NASH) were analyzed using NONMEM. Morphine and M3G PK were described by three- and one-compartment models, respectively. After accounting for the effect of total body weight on all clearance and volume of distribution parameters using an allometric scaling approach, NASH severity score (NASF; combination of fibrosis and nonalcoholic fatty liver disease activity scores) was the most significant predictor of differences in M3G exposure. The model predicted a linear decrease in the clearance of M3G with increasing NASF scores on a natural logarithmic scale. These results may provide some insight into the potential effect of NASH on the disposition of hepatic transporter substrates.

Renal function and symptoms/adverse effects in opioid-treated patients with cancer

BACKGROUND

Renal impairment and the risk of toxicity caused by accumulation of opioids and/or active metabolites is an under-investigated issue. This study aimed at analysing if symptoms/adverse effects in opioid-treated patients with cancer were associated with renal function.

METHODS

Cross-sectional multicentre study (European Pharmacogenetic Opioid Study, 2005-2008), in which 1147 adult patients treated exclusively with only one of the most frequently reported opioids (morphine/oxycodone/fentanyl) for at least 3 days were analysed. Fatigue, nausea/vomiting, pain, loss of appetite, constipation and cognitive dysfunction were assessed (EORTC QLQ-C30). Glomerular filtration rate (GFR) was estimated using Cockcroft-Gault (CG), Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI Creatinine) equations.

RESULTS

Mild to severe low GFR was observed among 40-54% of patients. CG equation showed that patients with mild and moderate/severe low GFR on morphine treatment had higher odds of having severe constipation (P < 0.01) than patients with normal GFR. In addition, patients with moderate/severe low GFR on morphine treatment were more likely to have loss of appetite (P = 0.04). No other significant associations were found.

CONCLUSION

Only severe constipation and loss of appetite were associated with low GFR in patients treated with morphine. Oxycodone and fentanyl, in relation to the symptoms studied, seem to be safe as used and titrated in routine cancer pain care.

Heroin crystal nephropathy

In this paper we present an interesting case of acute kidney injury and severe metabolic alkalosis in a patient with a history of heavy heroin abuse. Urine microscopy showed numerous broomstick-like crystals. These crystals are also identified in light and electron microscopy. We hypothesize that heroin crystalizes in an alkaline pH, resulting in tubular obstruction and acute kidney injury. Management is mainly supportive as there is no known specific therapy for this condition. This paper highlights the utility of urine microscopy in diagnosing the etiology of acute kidney injury and proposes a novel disease called heroin crystal nephropathy.

Pharmacological consequences of long-term morphine treatment in patients with cancer and chronic non-malignant pain

BACKGROUND

In patients with pain of malignant origin morphine may be administered in high and often increasing doses during extended periods of time. In patients with chronic pain of non-malignant origin morphine may be an important remedy, and in these cases the goal is to keep the morphine dose stable. The pharmacokinetic as well as the pharmacodynamic consequences of long-term morphine treatment with special reference to the two most important metabolites of morphine morphine-6-glucuronide (M-6-G) and morphine-3-glucuronide (M-3-G) remain to be settled.

METHODS

Assessments for pain, sedation and other morphine induced side effects were made several times for 19 cancer patients treated with changing doses of oral sustained release (SR) morphine and twice for 17 non-cancer patients treated with stable doses of SR morphine. Blood samples were obtained simultaneously and analysed for contents of morphine, M-3-G and M-6-G by high-performance liquid chromatography (HPLC).

RESULTS

Significant correlations were found between the daily dose of SR morphine and plasma morphine (r = 0.469, p < 0.01), plasma M-6-G (r = 0.677, p < 0.01), and plasma M-3-G ((r = 0.827, p < 0.01), in the cancer patient group, but only between the daily dose of SR morphine and plasma M-3-G (0.662, p < 0.01) and plasma M-6-G (0.571, p < 0.01) in the non-cancer patient group. Normalised M-3-G/M and M-6-G/M ratios for the cancer patient group were independent of duration of treatment and daily dose of SR morphine. Likewise in the non-cancer patient group duration of treatment did not influence the metabolite ratios. Correlations between pain score and plasma morphine, M-6-G and M-6-G/M were weak in the cancer patient as well as in the non-cancer patient group making it impossible to draw any conclusion regarding the potential contributory analgesic effect of M-6-G. Dryness of the mouth was the most frequent adverse effect reported in the non-cancer as well as the cancer patient group. In the latter group patients complaining of dryness of the mouth had significantly higher plasma morphine and M-6-G concentrations than patients who did not suffer from this side effect. This difference persisted (or was close to significance) when excluding patients receiving antidepressants.

CONCLUSION

In the cancer patient group neither dose nor treatment period seems to influence morphine glucuronidation. Likewise in the non-cancer patient group receiving stable doses of morphine duration of treatment does not seem to influence morphine glucuronidation. Dryness of the mouth was positively correlated to high plasma concentrations of morphine and M-6-G.

A systematic review of the use of opioid medication for those with moderate to severe cancer pain and renal impairment: a European Palliative Care Research Collaborative opioid guidelines project

BACKGROUND

Opioid use in patients with renal impairment can lead to increased adverse effects. Opioids differ in their effect in renal impairment in both efficacy and tolerability. This systematic literature review forms the basis of guidelines for opioid use in renal impairment and cancer pain as part of the European Palliative Care Research Collaborative's opioid guidelines project.

OBJECTIVE

The objective of this study was to identify and assess the quality of evidence for the safe and effective use of opioids for the relief of cancer pain in patients with renal impairment and to produce guidelines.

SEARCH STRATEGY

The Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, MedLine, EMBASE and CINAHL were systematically searched in addition to hand searching of relevant journals.

SELECTION CRITERIA

Studies were included if they reported a clinical outcome relevant to the use of selected opioids in cancer-related pain and renal impairment. The selected opioids were morphine, diamorphine, codeine, dextropropoxyphene, dihydrocodeine, oxycodone, hydromorphone, buprenorphine, tramadol, alfentanil, fentanyl, sufentanil, remifentanil, pethidine and methadone. No direct comparator was required for inclusion. Studies assessing the long-term efficacy of opioids during dialysis were excluded.

DATA COLLECTION AND ANALYSIS

This is a narrative systematic review and no meta-analysis was performed. The Grading of RECOMMENDATIONS Assessment, Development and Evaluation (GRADE) approach was used to assess the quality of the studies and to formulate guidelines.

MAIN RESULTS

Fifteen original articles were identified. Eight prospective and seven retrospective clinical studies were identified but no randomized controlled trials. No results were found for diamorphine, codeine, dihydrocodeine, buprenorphine, tramadol, dextropropoxyphene, methadone or remifentanil.

CONCLUSIONS

All of the studies identified have a significant risk of bias inherent in the study methodology and there is additional significant risk of publication bias. Overall evidence is of very low quality. The direct clinical evidence in cancer-related pain and renal impairment is insufficient to allow formulation of guidelines but is suggestive of significant differences in risk between opioids.

RECOMMENDATIONS

RECOMMENDATIONS regarding opioid use in renal impairment and cancer pain are made on the basis of pharmacokinetic data, extrapolation from non-cancer pain studies and from clinical experience. The risk of opioid use in renal impairment is stratified according to the activity of opioid metabolites, potential for accumulation and reports of successful or harmful use. Fentanyl, alfentanil and methadone are identified, with caveats, as the least likely to cause harm when used appropriately. Morphine may be associated with toxicity in patients with renal impairment. Unwanted side effects with morphine may be satisfactorily dealt with by either increasing the dosing interval or reducing the 24 hour dose or by switching to an alternative opioid.

The intravenous to oral relative milligram potency ratio of morphine during chronic dosing in cancer pain

Morphine (M) is the opioid analgesic of choice for severe cancer pain. The IV to PO M equipotent switch ratio (CR) is controversial. We designed this prospective observational cohort to confirm the efficacy and safety of M IV to PO CR of 1:3. Consecutive cancer patients admitted to an inpatient palliative medicine unit were screened for inclusion. Pain was managed by palliative medicine specialists. They were blinded to the patient data collected, and the calculated CR. The switch was considered successful if the following criteria were met: (1) Pain adequately controlled: pain rated as none or mild (2) Number of RD less than 4 (for non incident pain) per 24 hours (3) No limiting side effects. We used Day 3 ATC M dose for CR calculations. The major outcome measures were the IV : PO CR ratio, morphine doses (mg/day), pain severity, number of PRN doses, and day 1 and day 3side effects. Descriptive statistics were used to report mean, median, standard deviation and range of different variables. Two hundred and fifty six consecutive admissions were screened, and 106 were eligible for the study. Sixty two underwent a successful M route switch and were included in this analysis. A ratio of 1:3 was safely implemented over a wide M dose range. About 80% were successfully switched with a calculated CR of 1:3. 20% required an oral M dose adjustment after route switch either to better pain control or reduce side effects with a resultant higher (e.g. 1:4) or lower (e.g. 1:2) calculated potency ratios respectively. A potency ratio of 1:3 was safe as evaluated by common M side-effects, the dose also easy to calculate. The 1: 3 M IV to PO relative milligram potency ratio appears correct and practical for most patients over a wide M dose range.

Flexible dosing of tincture of opium in the management of opioid withdrawal: pharmacokinetics and pharmacodynamics

AIMS

The aim was to evaluate the clinical effectiveness, pharmacodynamics and pharmacokinetics of a range of Tincture of Opium (TOP) doses in the management of opioid withdrawal.

METHODS

Forty-five opium-dependent Thai subjects were allocated to three dosing groups (6.66, 13.3 and 20 mg morphine equivalents, twice daily) depending on their self-reported prior opium use. On day 5 of dosing subjects underwent an interdosing interval study where blood, withdrawal scores, heart rate and blood pressure (BP) were collected at 0, 1, 3 and 8 h. Plasma morphine concentrations were quantified by high-performance liquid chromatography, and plasma morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) concentrations by LCMS.

RESULTS

Thirty-two subjects completed the study. Withdrawal scores were low for all subjects (range 9-23% of maximum response). There were dose-dependent changes in both systolic and diastolic BP (P = 0.021 and P = 0.01, respectively), but these were not considered clinically significant. There were no effects of dose on respiratory rate. Plasma morphine concentrations changed significantly across the interdosing interval (P = 0.0001), rising to a maximum at 1 h after dosing. Plasma morphine concentrations also differed according to dose (P < 0.05). The mean ratios of the morphine glucuronides were found to be: M3G/M6G = 7.7, M3G/morphine = 35.6 and M6G/morphine = 4.9, values comparable to those previously reported.

CONCLUSION

The management of opioid withdrawal can be achieved, with minimal adverse effects, by using flexible dosing of TOP.

Cholestasis and endogenous opioids: liver disease and exogenous opioid pharmacokinetics

A class of endogenous opioids is upregulated in liver disease particular to cholestasis, which contributes to symptoms in liver disease such as pruritus, hypotension and encephalopathy. Symptoms associated with cholestasis are reversed or at least ameliorated by mu opioid receptor antagonists. Palliation of symptoms related to cholestatic liver disease also involves bile acid binding agents. Opioid receptor antagonists, unlike bile acid binding agents, have been reported to relieve multiple symptoms, except for pruritus, and improve liver function as demonstrated in experimental cholestasis. Exogenous opioid pharmacology is altered by liver disease. Dose reduction or prolongation of dose intervals is necessary depending on the severity of liver disease.

Developmental pharmacokinetics of morphine and its metabolites in neonates, infants and young children

BACKGROUND

Descriptions of the pharmacokinetics and metabolism of morphine and its metabolites in young children are scant. Previous studies have not differentiated the effects of size from those related to age during infancy.

METHODS

Postoperative children 0-3 yr old were given an intravenous loading dose of morphine hydrochloride (100 micro g kg(-1) in 2 min) followed by either an intravenous morphine infusion of 10 micro g h(-1) kg(-1) (n=92) or 3-hourly intravenous morphine boluses of 30 micro g kg(-1) (n=92). Additional morphine (5 micro g kg(-1)) every 10 min was given if the visual analogue (VAS, 0-10) pain score was >/=4. Arterial blood (1.4 ml) was sampled within 5 min of the loading dose and at 6, 12 and 24 h for morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). The disposition of morphine and formation clearances of morphine base to its glucuronide metabolites and their elimination clearances were estimated using non-linear mixed effects models.

RESULTS

The analysis used 1856 concentration observations from 184 subjects. Population parameter estimates and their variability (%) for a one-compartment, first-order elimination model were as follows: volume of distribution 136 (59.3) litres, formation clearance to M3G 64.3 (58.8) litres h(-1), formation clearance to M6G 3.63 (82.2) litres h(-1), morphine clearance by other routes 3.12 litres h(-1) per 70 kg, elimination clearance of M3G 17.4 (43.0) litres h(-1), elimination clearance of M6G 5.8 (73.8) litres h(-1). All parameters are standardized to a 70 kg person using allometric 3/4 power models and reflect fully mature adult values. The volume of distribution increased exponentially with a maturation half-life of 26 days from 83 litres per 70 kg at birth; formation clearance to M3G and M6G increased with a maturation half-life of 88.3 days from 10.8 and 0.61 litres h(-1) per 70 kg respectively at birth. Metabolite formation decreased with increased serum bilirubin concentration. Metabolite clearance increased with age (maturation half-life 129 days), and appeared to be similar to that described for glomerular filtration rate maturation in infants.

CONCLUSION

M3G is the predominant metabolite of morphine in young children and total body morphine clearance is 80% that of adult values by 6 months. A mean steady-state serum concentration of 10 ng ml(-1) can be achieved in children after non-cardiac surgery in an intensive care unit with a morphine hydrochloride infusion of 5 micro g h(-1) kg(-1) at birth (term neonates), 8.5 micro g h(-1) kg(-1) at 1 month, 13.5 micro g h(-1) kg(-1) at 3 months and 18 micro g h(-1) kg(-1) at 1 year and 16 micro g h(-1) kg(-1) for 1- to 3-yr-old children.

Opioids and renal function

Opioids, both endogenous and exogenous, have a strong influence on the renal function through different mechanisms, producing changes in the renal excretion of water and sodium. Several studies have demonstrated that opioids influence renal function, according to the agonist profile used. Mu, kappa, and delta agonists produce different renal effects, although the mechanisms remain unclear. Experimental data have given the input for a possible therapeutic role of kappa agonists for some specific conditions, for example, in treating water retention or hyponatremia occurring in patients who have hepatic cirrhosis with ascites. On the other hand, changes in renal function might strongly condition the use of opioids in the clinical setting, and the knowledge of the relationship between opioids and renal function is mandatory for a tailored approach to accommodate the individual responses in terms of pain intensity, tolerance, and adverse effects experienced by these groups of patients. The influence of renal function when using different opioids in the clinical setting is reviewed, as well as problems related to transplantation, renal damage induced by opioid addiction, and problems related to the use of opioid antagonists in such conditions.

PERSPECTIVE

Endogenous opioids exert physiologic effects on renal function, and the use of opioids may have an influence on renal activity. Renal impairment has a serious impact on the clearance of most opioids used in the clinical setting. Biochemical and clinical monitoring is mandatory to prevent serious complications.

Routine drug monitoring of serum concentrations of morphine, morphine-3-glucuronide and morphine-6-glucuronide do not predict clinical observations in cancer patients

The clinical importance of routine drug monitoring of serum concentrations of morphine, morphine-6-glucuronide (M6G) and morphine-3-glucuronide (M3G) during chronic morphine therapy is not established. We measured morphine, M6G and M3G serum concentrations in cancer pain patients receiving oral (n = 263, median dose 80 mg/24 hours) or subcutaneous (sc) (n = 35, median dose 110 mg/24 hours) morphine. Regression analyses were performed to investigate if serum concentrations of morphine, M3G and M6G predicted pain intensity (Brief Pain Inventory), health-related quality-of-life variables (EORTC QLQ-C30) and cognitive function (Mini-Mental Score). Serum concentrations were also compared in patients categorized as morphine 'treatment successes' and 'treatment failures'. We observed that serum concentrations of morphine, M6G or M3G did not predict pain intensity, cognitive function, nausea or tiredness. 'Treatment failures' caused by nausea, tiredness, cognitive failure or constipation did not have statistically significant different morphine, M6G and M3G serum concentrations than patients classified as 'treatment successes'. In conclusion, this study did not observe any concentration-effect relationships of morphine, M3G or M6G with pain intensity, nausea, constipation, tiredness or cognitive failure in blood samples obtained during routine clinical drug monitoring in cancer patients. This result suggests that therapeutic drug monitoring as a routine tool during chronic morphine treatment has limited value for clinical decision making.

Relationships among morphine metabolism, pain and side effects during long-term treatment: an update

The two metabolites of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), have been studied intensively in animals and humans during the past 30 years in order to elucidate their precise action and possible contribution to the desired effects and side effects seen after morphine administration. M3G and M6G are formed by morphine glucuronidation, mainly in the liver, and are excreted by the kidneys. The metabolites are found in the cerebrospinal fluid after single as well as multiple doses of morphine. M6G binds to opioid receptors, and animal studies have demonstrated that M6G may be a more potent analgesic than morphine. Results from human studies regarding the analgesic effect of M6G are not unanimous. The potency ratio between systemic M6G and morphine in humans has not been settled, but is probably lower than previously assumed. Hitherto, only a few studies have found evidence for a contributory effect of M6G to the overall effects observed after morphine administration. Several studies have demonstrated that administration of M6G is accompanied by fewer and a milder degree of opioid-like side effects than observed after morphine administration, but most of the studies have used lower doses of M6G than of morphine. M3G displays very low affinity for opioid receptors and has no analgesic activity. Animal studies have shown that M3G may antagonize the analgesic effect of morphine and M6G, but no human studies have demonstrated this. M3G has also been connected to certain neurotoxic symptoms, such as hyperalgesia, allodynia and myoclonus, which have been observed after administration of M3G or high doses of morphine in animals. The symptoms have been reported sporadically in humans treated primarily with high doses of morphine, but the role of M3G in eliciting the symptoms is not fully elucidated.

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

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

Pain, sedation and morphine metabolism in cancer patients during long-term treatment with sustained-release morphine

BACKGROUND

Morphine-6-glucuronide (M-6-G) and morphine-3-glucuronide (M-3-G) are the two most important metabolites of morphine. Both are pharmacologically active, however, with different effects. M-6-G has been demonstrated capable of inducing anti-nociception and sedation, and M-3-G may induce behavioural excitation and possibly antagonise anti-nociception. Their impact on pharmacodynamics in patients in long-term treatment with oral morphine remains to be settled.

METHODS

Forty-two cancer patients treated with oral sustained-release (SR) morphine were assessed for pain, sedation and other side effects related to morphine treatment. Blood samples were analysed for morphine, M-3-G and M-6-G by high-performance liquid chromatography (HPLC).

RESULTS

Significant correlations were found between the daily dose of SR morphine and plasma morphine (M) (r = 0.535, P < 0.001), plasma M-6-G (r = 0.868, P < 0.001) and plasma M-3-G (r = 0.865, P < 0.001). There was no relationship between plasma morphine, M-6-G, M-6-G/M and pain and sedation scores. Seventy-nine percent of the patients suffered from dryness of the mouth, which was the most frequent side effect observed. Patients in this group had higher plasma morphine and M-6-G concentrations than patients who did not suffer from this side effect.

CONCLUSION

The plasma concentrations of morphine and its metabolites, M-3-G and M-6-G, are significantly correlated to the daily dose of SR morphine. Although M-6-G has analgesic properties, no associations were found between pain and plasma morphine and morphine metabolites. This may be due to the multitudinous factors affecting the dose-effect relationship. Patients with dryness of the mouth had higher concentrations of morphine and M-6-G than patients without this side effect.

Changing M3G/M6G ratios and pharmacodynamics in a cancer patient during long-term morphine treatment

A cancer patient receiving long-term oral sustained-release morphine treatment and periodically presenting with unusually high plasma M3G/M6G ratios is described. We found the patient's formation of M6G more unstable and perhaps delayed compared to the formation of M3G. There is no apparent explanation for this phenomenon and the high M3G/M6G ratios had no implications for the patient's pain experience or side effects from the morphine treatment.

Pharmacokinetics of morphine and its glucuronidated metabolites in burn injuries

OBJECTIVE

To investigate the effects of major thermal burn injury and continuous intravenous morphine infusion on the disposition of morphine and its glucuronidated metabolites, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) once a week for three weeks.

CASE SUMMARIES

Five patients with major first-, second-, or third-degree burn injuries received long-term intravenous morphine infusion. The required dose varied greatly (from 4 to 39.5 mg/h). The steady-state concentrations of morphine, M3G, and M6G ranged from 20 to 452, 29 to 3436, and 20 to 1240 mumol/L, respectively. The systemic clearance (Cls) of morphine ranged from 14.8 to 40.3 mL/min/kg and did not change over time. The ratios of M6G and M3G to morphine were not affected by dose, even with the wide variation of intravenous dosage. Morphine kinetics appeared to be first-order. Mean recovery of morphine, M3G, and M6G in urine was 1.7 +/- 1.0%, 42.0 +/- 16.8%, and 11.8 +/- 3.2%, respectively, and renal clearance ranged from 8 to 64, 26 to 325, and 59 to 589 mL/min, respectively. Mean pain intensity ratings at rest remained low and stable (0.7 +/- 0.9 on day 7, 0.4 +/- 0.3 on day 14, 0 +/- 0 on day 21).

DISCUSSION

To our knowledge, this is the first published report describing morphine, M3G, and M6G disposition in patients with major thermal burn injury. The Cls of morphine is similar to that observed in other patient populations and healthy subjects, suggesting that the presence of major burn injuries or a continuous morphine infusion over a three-week period may not contribute significantly to the variability among individuals. In these cases, the renal clearance of morphine and its glucuronides was within the range of values reported for other populations of patients and healthy subjects. Recovery of morphine and its glucuronides in urine was also similar to that in healthy individuals.

CONCLUSIONS

These cases suggest that the effects of major burn injuries and of long-term intravenous infusion of morphine did not seem to modify morphine, M3G, and M6G disposition. Among patients with burn injuries, the severity of burns of duration of administration are not a cause of nonlinear kinetic of morphine or of morphine resistance. The morphine infusion rate was substantially variable and not directly related to its clearance, suggesting that monitoring of morphine should be focused on the clinical response.

A pharmacodynamic study of morphine and its glucuronide metabolites after single morphine dosing in cancer patients with pain

Eleven morphine naïve patients with cancer-related pain were given a single dose of either intravenous morphine (n = 5) or oral morphine (n = 6). Blood sampling was performed over a 24-hr period and serial pain assessments were made using a categorical scale. Plasma samples were analyzed for morphine, morphine-6-glucuronide (M-6-G), morphine-3-glucuronide (M-3-G), and normorphine using high-performance liquid chromatography. In neither the intravenous nor oral group was there a correlation between analgesia duration and the half-lives of morphine and M-6-G. There was no correlation between the time to peak analgesia and time to peak concentration for morphine or M-6-G. There was no significant difference in absolute concentrations of M-6-G or M-3-6 nor in the ratio of M-3-G to M-6-G at peak analgesia versus relapse.

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.

Plasma morphine and glucuronide (M3G and M6G) concentrations in hospice inpatients

Plasma morphine, morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) concentrations were quantified by high performance liquid chromatography (HPLC) in 36 hospice inpatients receiving morphine orally or subcutaneously. The data were analyzed in relation to dose, serum creatinine, serum gamma glutamyl transferase, and presence or absence of opioid-induced adverse effects. There were significant associations (P < 0.05) between plasma morphine, M3G (subcutaneous route only), and M6G concentrations and dose for both routes of administration. The mean dose-corrected plasma morphine concentration for the subcutaneous group was three times that of the oral group, confirming present oral to subcutaneous dose conversion practices. Nineteen patients experienced symptoms attributed to morphine: nausea and vomiting in ten and acute delirium in nine. Serum creatinine was elevated in patients with adverse effects (P = 0.031), as were the dose-corrected plasma M3G (P = 0.029) and M6G (P = 0.043) concentrations. All seven patients with serum creatinine concentrations above the normal range had symptoms attributed to opioid-induced adverse effects. Plasma M3G, M6G, and dose-corrected plasma M3G and M6G concentrations were significantly (P < 0.001) higher in these patients than in those with normal serum creatinine concentrations. The data indicate that accumulation of M3G and M6G may be a causal or aggravating factor in the nausea and vomiting and cognitive function profile of palliative and terminal care patients with significant renal function impairment.

Epidural and subcutaneous morphine in the management of cancer pain: a double-blind cross-over study

Ten patients who suffered from severe cancer-related pain participated in a randomised, double-blind and cross-over study to compare the effectiveness and acceptability of epidural and subcutaneous administration of morphine. The patients titrated themselves pain-free in 48 h using a patient controlled analgesia system. The median daily doses calculated from the consumption of the last 4-h study period were 372 mg for subcutaneous and 106 mg for epidural administration. The two modes of morphine administration turned out to be comparable in terms of both effectiveness and acceptability. Both treatments provided better pain relief with less adverse effects compared with the prestudy oral morphine treatment.

Ethanol interference with morphine metabolism in isolated guinea pig hepatocytes

It has previously been shown that guinea pig hepatocytes metabolise morphine in a fashion similar to humans. The metabolism of morphine (5 muM) and the formation of metabolites morphine-3-glucuronide, morphine-6-glucuronide and normorphine was studied in the absence and presence of ethanol (5, 10, 25, 60 and 100 mM) in freshly isolated guinea pig hepatocytes. In order to gain more detailed information, a mathematical model was estimated on experimental data and used to analyse the effects of ethanol on the reaction rates of the different morphine metabolites. Ethanol inhibited the rate of morphine elimination in a dose-related manner, at the high ethanol concentrations the elimination rate was 40 per cent of the control rate. The formation of morphine-glucuronides was influenced in a biphasic manner. Five and 10 mM ethanol increased both the morphine-3-glucuronide and morphine-6-glucuronide levels after 60 min incubation compared to the control, whereas at the higher ethanol concentrations (25-100 mM) the levels of morphine-glucuronides were reduced. Data from the mathematical model, however, demonstrated that the reaction rates for morphine-glucuronide formation were decreased at all ethanol concentrations and in a dose-dependent manner, the interpretation of this being that at the lower (5 and 10 mM) ethanol concentrations employed in this study, other metabolic pathways of morphine are more heavily inhibited than the glucuronidations, resulting in a shunting towards morphine-3-glucuronide and morphine-6-glucuronide. The pharmacodynamic consequences of these pharmacokinetic effects are thus somewhat difficult to predict since morphine-6-glucuronide has a higher agonist potency than morphine. At high concentrations ethanol inhibition of morphine metabolism will increase the concentration of morphine and subsequently the euphoric and the toxic effects. The lower quantities of morphine-6-glucuronide formed in the presence of high ethanol concentrations on the other hand most probably imply reduction of such effects and the net pharmacodynamic effect would be uncertain. At low ethanol concentrations, however, morphine-6-glucuronide concentrations increased and morphine metabolism was less inhibited leading to a possible potentiation of the effects of morphine. Thus, a low ethanol concentration might exert a more pronounced ethanol-drug effect interaction than a higher ethanol concentration.

Pharmacokinetics of epidurally administered nicomorphine with its metabolites and glucuronide conjugates in patients undergoing pulmonary surgery during combined epidural local anaesthetic block and general anaesthesia

After epidural administration of 15 mg 3, 6-dinicotinoylmorphine (nicomorphine) in 10 patients undergoing pulmonary surgery, the parent compound was quickly metabolized into the metabolites 6-mononicotinoylmorphine and morphine. The mean apparent half-lives (+/- SD) of elimination were 10 min (0.165 h +/- 0.053 h) for 3,6-dinicotinoylmorphine and 1.77 h +/- 1.23 h for 6-mononicotinoylmorphine. Morphine is subsequently metabolized into morphine-3-glucuronide and morphine-6-glucuronide. The apparent half-lives of morphine, morphine-3-glucuronide, and morphine-6-glucuronide are similar: 3.63 h +/- 1.63 h, 4.10 h +/- 0.57 h, and 4.20 h +/- 1.64 h respectively. The possible glucuronide conjugate of 6-mononicotinoylmorphine was not detected. The prodrug 3,6-dinicotinoylmorphine was biotransformed into three active compounds: 6-mononicotinoylmorphine, morphine, and morphine-6-glucuronide.

Atypical absorption of morphine sulphate through oral mucosa: an unusual case of acute opioid poisoning

An unusual case of probable opioid poisoning due to atypical absorption of morphine sulphate through the oral mucosa is reported. A patient with advanced laryngeal cancer, who was unable to swallow, became stuporous, bradypneic, and cyanotic and had pinpoint pupils 1 hour after taking a controlled-release tablet of morphine sulphate 30 mg. Intravenous naloxone 0.4 mg induced prompt reversal of the clinical picture. The tablet of morphine, in advanced stage of decomposition, was found in the patient's mouth, the mucosa of which was inflamed and extensively ulcerated because of the long-standing stagnation of food residuals. Usually morphine is not amenable to transmucosal absorption, because of its low lipid solubility. In this case, the retention of the tablet of morphine in the mouth and the breakdown of oral mucosa integrity could have provoked a quick transmucosal absorption of the drug, with by-pass of hepatic first-pass metabolism. This may have induced a peak in drug concentration much higher than that usually resulting from the enteric absorption of controlled-release tablets of morphine.

Rectal administration of nicomorphine in patients improves biological availability of morphine and its glucuronide conjugates

The pharmacokinetics of 30 mg nicomorphine after rectal administration with a suppository are described in 8 patients under combined general and epidural anaesthesia. No nicomorphine or 6-mononicotinoylmorphine could be detected in the serum. Morphine appeared almost instantaneously with a lag-time of 8 min and had a final elimination half-life of 1.48 +/- 0.48 h. Morphine was metabolized to morphine-3-glucuronide and morphine-6-glucuronide. These glucuronide conjugates appeared after a lag-time of 12 min and the half-life of these two glucuronide conjugates was similar: about 2.8 h (P > 0.8). The glucuronide conjugate of 6-mononicotinoylmorphine was not detected. In the urine only morphine and its glucuronides were found. The renal clearance value for morphine was 162 ml.min-1 and for the glucuronides 81 ml.min-1. This study shows that administration of a suppository with 30 mg nicomorphine gives an excellent absolute bioavailability of morphine and its metabolites of 88%. The lipid-soluble prodrug nicomorphine is quickly absorbed and immediately hydrolysed to morphine.

Morphine and morphine-glucuronide concentrations in plasma and CSF during long-term administration of oral morphine

Concentrations of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) were measured by h.p.l.c. in plasma and cerebrospinal fluid (CSF) samples from 16 patients with cancer receiving oral (controlled-release) morphine. There was a close correlation between plasma and CSF morphine concentrations (r = 0.94, P = 0.0001) and both correlated with drug dosage (r = 0.61, P = 0.013 and r = 0.74, P = 0.0001, respectively). M3G and M6G in plasma and CSF were correlated (r = 0.81 and r = 0.82, both P = 0.0001). No relationship was apparent between M plus M6G concentrations in the CSF and pain scores.

Morphine-6-glucuronide: a potent stimulator of locomotor activity in mice

The present study tested the hypothesis that morphine glucuronides have stimulant properties by studying their effects on locomotor activity in mice. Drug-naive C57BL/6J male mice were injected with saline, morphine, morphine-6-glucuronide (M6G) or morphine-3-glucuronide (M3G). In some experiments, mice were injected with saline or naloxone 5 min prior to drug treatment. Injection of 40 mg/kg morphine or M6G, but not M3G, significantly increased activity versus saline. The extent of activation induced by M6G was markedly higher than for morphine. Subsequent dose-response studies across a somewhat lower dose range using equimolar doses of morphine and M6G (3-80 mumoles/kg) found that both drugs significantly increased locomotor activity beginning at 20 mumoles/kg. M6G increased locomotor activity from 1.3 to 2.1 times more than for equimolar doses of morphine. Pretreatment with naloxone (10 mg/kg) completely abolished the locomotor stimulation induced by 32 mumoles/kg morphine and M6G. These findings present evidence that M6G is an active metabolite of morphine which has behaviorally stimulating effects and may play an important role in mediating the reinforcing properties of morphine in humans.