Pharmacokinetics of morphine and its glucuronides following intravenous administration of morphine in patients undergoing continuous ambulatory peritoneal dialysis

Implementing physics-based digital patient twins to tailor the switch of oral morphine to transdermal fentanyl patches based on patient physiology

Fentanyl transdermal patches are widely implemented for cancer-induced pain treatment due to the high potency of fentanyl and gradual drug release. However, transdermal fentanyl up-titration for opioid-naïve patients is difficult, which is why opioid treatment is often started with oral/iv morphine. Based on the daily dose of morphine, the initial dose of the fentanyl patch is decided upon. After reaching a stable level of pain, the switch is made from oral/iv morphine to transdermal fentanyl. There are standard calculation tools for transferring from oral/iv morphine to transdermal fentanyl, which is the same for all patients. By considering the variations in the physiology of the patients, a unique switching strategy cannot meet the needs of different patients. This study explores the outcome in terms of pain relief and minute ventilation during opioid therapy. For this, we used physics-based simulations on a virtually-generated population of patients, and we applied the same therapy to all patients. We could show that patients' physiology, such as gender, age, and weight, greatly impact the outcome of the therapy; as such, the correlation coefficient between pain intensity and age is 0.89, and the correlation coefficient between patient's weight and maximum plasma concentration of morphine and fentanyl is -0.98 and -0.97. Additionally, a different combination of the duration of overlap between morphine and fentanyl therapy with different doses of fentanyl was considered for the virtual patients to find the best opioid-switching strategy for each patient. We explored the impact of combining physiological features to determine the best-suited strategy for virtual patients. Our findings suggest that tailoring morphine and fentanyl therapy only based on a limited number of features is insufficient, and increasing the number of impactful physiological features positively influences the outcome of the therapy.

Heroin and its metabolites: relevance to heroin use disorder

Heroin is an opioid agonist commonly abused for its rewarding effects. Since its synthesis at the end of the nineteenth century, its popularity as a recreational drug has ebbed and flowed. In the last three decades, heroin use has increased again, and yet the pharmacology of heroin is still poorly understood. After entering the body, heroin is rapidly deacetylated to 6-monoacetylmorphine (6-MAM), which is then deacetylated to morphine. Thus, drug addiction literature has long settled on the notion that heroin is little more than a pro-drug. In contrast to these former views, we will argue for a more complex interplay among heroin and its active metabolites: 6-MAM, morphine, and morphine-6-glucuronide (M6G). In particular, we propose that the complex temporal pattern of heroin effects results from the sequential, only partially overlapping, actions not only of 6-MAM, morphine, and M6G, but also of heroin per se, which, therefore, should not be seen as a mere brain-delivery system for its active metabolites. We will first review the literature concerning the pharmacokinetics and pharmacodynamics of heroin and its metabolites, then examine their neural and behavioral effects, and finally discuss the possible implications of these data for a better understanding of opioid reward and heroin addiction. By so doing we hope to highlight research topics to be investigated by future clinical and pre-clinical studies.

Allergenic and Mas-Related G Protein-Coupled Receptor X2-Activating Properties of Drugs: Resolving the Two

Since the seminal description implicating occupation of the Mas-related G protein-coupled receptor X2 (MRGPRX2) in mast cell (MC) degranulation by drugs, many investigations have been undertaken into this potential new endotype of immediate drug hypersensitivity reaction. However, current evidence for this mechanism predominantly comes from (mutant) animal models or in vitro studies, and irrefutable clinical evidence in humans is still missing. Moreover, translation of these preclinical findings into clinical relevance in humans is difficult and should be critically interpreted. Starting from our clinical priorities and experience with flow-assisted functional analyses of basophils and cultured human MCs, the objectives of this rostrum are to identify some of these difficulties, emphasize the obstacles that might hamper translation from preclinical observations into the clinics, and highlight differences between IgE- and MRPGRX2-mediated reactions. Inevitably, as with any subject still beset by many questions, alternative interpretations, hypotheses, or explanations expressed here may not find universal acceptance. Nevertheless, we believe that for the time being, many questions remain unanswered. Finally, a theoretical mechanistic algorithm is proposed that might advance discrimination between MC degranulation from MRGPRX2 activation and cross-linking of membrane-bound drug-reactive IgE antibodies.

Regular, low-dose methadone for reducing breathlessness in people experiencing or at risk of neurotoxic effects from morphine: A single-center case series

Breathlessness is a common symptom suffered by people living with advanced malignant and non-malignant diseases, one which significantly limits their quality of life. If it emerges at minimal exertion, despite the maximal, guidelines-directed, disease-specific therapies, it should be considered persistent and obliges clinicians to prescribe symptomatic, non-pharmacological, and pharmacological treatment to alleviate it. Opioids are recommended for the symptomatic treatment of persistent breathlessness, with morphine most extensively studied for this indication. It is extensively metabolized in the liver into water-soluble 3- and 6-glucuronides, excreted by the kidneys. In the case of advanced renal failure, the glucuronides accumulate, mainly responsible for toxicity 3-glucuronides. Some people, predominantly those with advanced renal failure, develop neurotoxic effects after chronic morphine, even when prescribed at a very low dose. A single-center case series of consecutive patients experiencing neurotoxic effects after long-term, low-dose morphine or at risk of such effects were transferred to methadone to avoid the accumulation of neurotoxic metabolites. Over the course of 4.5 years, 26 patients have been treated with methadone in the median dose of 3.0 mg/24 h p.o., for persisting breathlessness. Sixteen of them had been treated previously with an opioid (usually morphine) at the median dose of 7.0 mg/24 h (morphine oral daily dose equivalent). They were transferred to methadone, with the median dose of 3.0 mg/24 h orally (methadone oral daily dose equivalent), and the median morphine-to-methadone dose ratio was 2.5:1. All patients experienced a meaningful improvement in breathlessness intensity after methadone, by a median of 5 points (range 1-8) on the 0-10 numerical rating scale (NRS) in the whole group, and by 2 points (range 0-8) in those pretreated with other opioids, mainly morphine. Low-dose methadone can be considered an efficient alternative to morphine for reducing breathlessness in people experiencing neurotoxic effects or at risk of developing them following treatment with morphine.

MRGPRX2 and Adverse Drug Reactions

Many adverse reactions to therapeutic drugs appear to be allergic in nature, and are thought to be triggered by patient-specific Immunoglobulin E (IgE) antibodies that recognize the drug molecules and form complexes with them that activate mast cells. However, in recent years another mechanism has been proposed, in which some drugs closely associated with allergic-type events can bypass the antibody-mediated pathway and trigger mast cell degranulation directly by activating a mast cell-specific receptor called Mas-related G protein-coupled receptor X2 (MRGPRX2). This would result in symptoms similar to IgE-mediated events, but would not require immune priming. This review will cover the frequency, severity, and dose-responsiveness of allergic-type events for several drugs shown to have MRGPRX2 agonist activity. Surprisingly, the analysis shows that mild-to-moderate events are far more common than currently appreciated. A comparison with plasma drug levels suggests that MRGPRX2 mediates many of these mild-to-moderate events. For some of these drugs, then, MRGPRX2 activation may be considered a regular and predictable feature after administration of high doses.

Analyses of Respiratory Depression Associated with Opioids in Cancer Patients Based on the Japanese Adverse Drug Event Report Database

Opioid-induced respiratory depression is a potentially life-threatening adverse drug event. The purpose of this study was to evaluate the incidence of respiratory depression using the Japanese Adverse Drug Event Report (JADER) Database to obtain data to promote proper use of opioids. The JADER database from April 2004 to March 2017 was obtained from the Pharmaceuticals and Medical Devices Agency. We calculated the reporting odds ratios (RORs) of suspected opioids (morphine, fentanyl, oxycodone, tapentadol, methadone, tramadol, pentazocine, buprenorphine, and codeine phosphate hydrate), analyzed the daily dose at first appearance and the time-to-onset profile, and assessed the hazard type using the Weibull shape parameter. ROR analysis detected adverse event signals for all opioids. Morphine showed a large ROR value with statistical significance in elderly (≥70 years old) patients. The median daily doses of oral morphine and oxycodone for inducing respiratory depression were comparably low (30 mg/d as oral morphine equivalent dose), while that of transdermal fentanyl was 120 mg/d (oral morphine equivalent dose). On time-to-onset analysis using the Weibull distribution, those opioids were classified as the early failure type. The median time-to-onset of oral morphine, oral oxycodone and transdermal fentanyl was 5.5, 11 and 12.5 d, respectively, and almost 50% of cases were reported within 30 d. Taken together, our results suggest that it is important to monitor patients carefully for at least the first one week to one month, even if opioids are administered at a relatively low dose, especially in elderly patients administered morphine.

Morphine Use in Renal Failure: A Case Report of Single-Dose Morphine Toxicity in a Patient Requiring Peritoneal Dialysis

OBJECTIVE

We describe a case of morphine toxicity presumably caused by accumulation of its active metabolite morphine-6-glucuronide (M6G) secondary to reduced clearance by peritoneal dialysis.

METHODS

We present the relevant history and laboratory data and review pertinent literature regarding the use of opioids in renal failure.

RESULTS

A 76-year-old African-American female received one dose of morphine sulfate and developed signs and symptoms of morphine toxicity for 2 days, even after multiple peritoneal dialysis sessions.

CONCLUSION

Because of reduced renal clearance of morphine and its metabolites in patients requiring peritoneal dialysis, morphine should be avoided as an analgesic option in this population due to increased risk of morphine toxicity.

Acute Pain Management Pharmacology for the Patient with Concurrent Renal or Hepatic Disease

The clinical utility of most analgesic drugs is altered in the presence of patients with impaired renal or hepatic function not simply because of altered clearance of the parent drug, but also through production and accumulation of toxic or therapeutically active metabolites. Some analgesic agents may also aggravate pre-existing renal and hepatic disease.

A search was performed, taking in published articles and pharmaceutical data to determine available evidence for managing acute pain effectively and safely in these two patient groups. The resulting information consisted mainly of small group pharmacokinetic studies or case reports, which included a large variation in degree of organ dysfunction.

In the presence of renal impairment, those drugs which exhibit the safest pharmacological profile are alfentanil, buprenorphine, fentanyl, ketamine, paracetamol (except with compound analgesics), remifentanil and sufentanil: none of these deliver a high active metabolite load, or suffer from significantly prolonged clearance. Amitriptyline, bupivacaine, clonidine, gabapentin, hydromorphone, levobupivacaine, lignocaine, methadone, mexiletine, morphine, oxycodone and tramadol have been used in the presence of renal failure, but do require specific precautions, usually dose reduction. Aspirin, dextropropoxyphene, non-steroidal anti-inflammatory drugs and pethidine, should not be used in the presence of chronic renal failure due to the risk of significant toxicity.

In the presence of hepatic impairment, most drugs are subject to significantly impaired clearance and increased oral bioavailability, but are poorly studied in the clinical setting. The agent least subject to alteration in this context is remifentanil; however the drugs’ potency has other inherent dangers. Other agents must only be used with caution and close patient monitoring. Amitriptyline, carbamazepine and valproate should be avoided as the risk of fulminant hepatic failure is higher in this population, and methadone is contraindicated in the presence of severe liver disease.

Restless Legs Syndrome in Patients With Chronic Kidney Disease

Symptoms of restless legs syndrome (RLS) are common in patients with chronic kidney disease (CKD) on dialysis; symptoms of RLS are estimated to affect up to 25% of patients on dialysis when the international RLS diagnostic criteria are applied. RLS is a neurologic disorder with a circadian rhythmicity characterized by an overwhelming urge to move the legs during rest, which can be relieved temporarily by movement. RLS has been associated with an increase in sleep disturbance, higher cardiovascular morbidity, decreased quality of life, and an increased risk of death in patients with CKD. Although the exact pathophysiology of RLS is unknown, it is thought to involve an imbalance in iron metabolism and dopamine neurotransmission in the brain. The symptoms of moderate to severe RLS can be treated with several pharmacologic agents; however, data specific to patients on dialysis with RLS are lacking. The purpose of this article is to examine the relationship between, and complications of, RLS and CKD both in dialysis and nondialysis patients, and discuss the treatment options for patients on dialysis with RLS.

Morphine Glucuronidation and Elimination in Intensive Care Patients: A Comparison with Healthy Volunteers

BACKGROUND

Although morphine is used frequently to treat pain in the intensive care unit, its pharmacokinetics has not been adequately quantified in critically ill patients. We evaluated the glucuronidation and elimination clearance of morphine in intensive care patients compared with healthy volunteers based on the morphine and morphine-3-glucuronide (M3G) concentrations.

METHODS

A population pharmacokinetic model with covariate analysis was developed with the nonlinear mixed-effects modeling software (NONMEM 7.3). The analysis included 3012 morphine and M3G concentrations from 135 intensive care patients (117 cardiothoracic surgery patients and 18 critically ill patients), who received continuous morphine infusions adapted to individual pain levels, and 622 morphine and M3G concentrations from a previously published study of 20 healthy volunteers, who received an IV bolus of morphine followed by a 1-hour infusion.

RESULTS

For morphine, a 3-compartment model best described the data, whereas for M3G, a 1-compartment model fits best. In intensive care patients with a normal creatinine concentration, a decrease of 76% was estimated in M3G clearance compared with healthy subjects, conditional on the M3G volume of distribution being the same in intensive care patients and healthy volunteers. Furthermore, serum creatinine concentration was identified as a covariate for both elimination clearance of M3G in intensive care patients and unchanged morphine clearance in all patients and healthy volunteers.

CONCLUSIONS

Under the assumptions in the model, M3G elimination was significantly decreased in intensive care patients when compared with healthy volunteers, which resulted in substantially increased M3G concentrations. Increased M3G levels were even more pronounced in patients with increased serum creatinine levels. Model-based simulations show that, because of the reduction in morphine clearance in intensive care patients with renal failure, a 33% reduction in the maintenance dose would result in morphine serum concentrations equal to those in healthy volunteers and intensive care patients with normal renal function, although M3G concentrations remain increased. Future pharmacodynamic investigations are needed to identify target concentrations in this population, after which final dosing recommendations can be made.

Chronic opioid pain management for chronic kidney disease

Questions from patients about pain conditions, pain treatment, and responses from authors are presented to help educate patients and make them effective self-advocates. The topics addressed in this issue are renal or kidney failure and chronic pain management with opioids, morphine, and oxycodone effect in the body over a period of time. This includes process of absorption, distribution, localization in tissues, biotransformation and excretion in chronic kidney disease, expected side effects and recommendations.

Induction of morphine-6-glucuronide synthesis by heroin self-administration in the rat

RATIONALE

Heroin is rapidly metabolized to morphine that in turn is transformed into morphine-3-glucuronide (M3G), an inactive metabolite at mu-opioid receptor (MOR), and morphine-6-glucuronide (M6G), a potent MOR agonist. We have found that rats that had received repeated intraperitoneal injections of heroin exhibit measurable levels of M6G (which is usually undetectable in this species).

OBJECTIVE

The goal of the present study was to investigate whether M6G synthesis can be induced by intravenous (i.v.) heroin self-administration (SA).

MATERIALS AND METHODS

Rats were trained to self-administer either heroin (50 μg/kg per infusion) or saline for 20 consecutive 6-h sessions and then challenged with an intraperitoneal challenge of 10 mg/kg of heroin. Plasma levels of heroin, morphine, 6-mono-acetyl morphine, M3G, and M6G were quantified 2 h after the challenge. In vitro morphine glucuronidation was studied in microsomal preparations obtained from the liver of the same rats.

RESULTS

Heroin SA induced the synthesis of M6G, as indicated by detectable plasma levels of M6G (89.7 ± 37.0 ng/ml vs. 7.35 ± 7.35 ng/ml after saline SA). Most important, the in vitro V (max) for M6G synthesis was correlated with plasma levels of M6G (r (2) = 0.78). Microsomal preparations from saline SA rats produced negligible amounts of M6G.

CONCLUSION

Both in vivo and in vitro data indicate that i.v. heroin SA induces the synthesis of M6G. These data are discussed in the light of previous studies conducted in heroin addicts indicating that in humans heroin enhances the synthesis of the active metabolite of heroin and morphine.

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.

Implications of opioid analgesia for medically complicated patients

Opioid analgesics have an established role in the management of postoperative pain and cancer pain, and are gaining acceptance for the management of moderate to severe chronic noncancer pain, most notably chronic low back pain and osteoarthritis, that does not respond to other interventions. Many patients with chronic pain have co-morbid medical conditions that may complicate opioid therapy. Selecting the appropriate opioid requires knowledge of how individual opioids differ with respect to metabolism and interaction with concurrent medications, as well as the reasons why specific medical conditions may influence their efficacy and tolerability. Polypharmacy is a common complicating condition in the elderly and in patients with psychiatric illness, cancer, cardiovascular disease, diabetes mellitus or other chronic illnesses. Polypharmacy, though often necessary for patients with multiple medical conditions, also multiplies the risk of drug interactions. Pharmacokinetic drug interactions can increase or reduce exposure to the opioid or concurrent medications, reducing efficacy and/or tolerability and increasing toxicity. Pharmacodynamic interactions can enhance the depressive effects of opioids, compromising safety. Patients with impaired renal or hepatic function may have difficulty clearing or metabolizing opioids and concurrent medications, leading to increased risk of adverse events. Patients with cardiovascular, cerebrovascular or respiratory disease (including smokers of >/=2 packs/day with no other diagnosis) may be more susceptible to respiratory depression, bradycardia and hypotension with any opioid, and a few specific opioids pose additional risks. Patients with cerebrovascular disease, dementia, brain injury or psychiatric illness are more susceptible to opioid effects on the CNS, which can include euphoria, cognitive impairment and sedation. Appropriate opioid selection may mitigate these effects. Even in older patients, addiction, abuse and misdirection of prescribed opioids are of concern. Higher risk exists for patients with psychiatric illness, history of substance abuse, and identifiable substance abuse risk factors. Screening for abuse potential and vigilant patient monitoring should be routine. Opioids differ in their ability to produce euphoria, based on opioid receptor agonism, but substance abusers may be more influenced by availability, familiarity and cost factors. Consequently, opioid selection has limited influence on abuse potential but can facilitate ease of monitoring. This review provides an overview of opioid use in medically complicated patients and recommendations on how to optimize analgesia while avoiding adverse events and drug interactions in the clinical setting. Articles cited in this review were identified via a search of EMBASE and PubMed. Articles selected for inclusion discussed characteristics of specific opioids and general physiological aspects of opioid therapy in important patient populations.

Opioid metabolism

Clinicians understand that individual patients differ in their response to specific opioid analgesics and that patients may require trials of several opioids before finding an agent that provides effective analgesia with acceptable tolerability. Reasons for this variability include factors that are not clearly understood, such as allelic variants that dictate the complement of opioid receptors and subtle differences in the receptor-binding profiles of opioids. However, altered opioid metabolism may also influence response in terms of efficacy and tolerability, and several factors contributing to this metabolic variability have been identified. For example, the risk of drug interactions with an opioid is determined largely by which enzyme systems metabolize the opioid. The rate and pathways of opioid metabolism may also be influenced by genetic factors, race, and medical conditions (most notably liver or kidney disease). This review describes the basics of opioid metabolism as well as the factors influencing it and provides recommendations for addressing metabolic issues that may compromise effective pain management. Articles cited in this review were identified via a search of MEDLINE, EMBASE, and PubMed. Articles selected for inclusion discussed general physiologic aspects of opioid metabolism, metabolic characteristics of specific opioids, patient-specific factors influencing drug metabolism, drug interactions, and adverse events.

Current concepts in pain management: pharmacologic options for the pediatric, geriatric, hepatic and renal failure patient

This article provides a review for current practice. Strict guidelines are not available on some topics, and they may never be drafted because pain is such a unique individual experience. It is recommended to coordinate care with other medical specialties when patients present with organ dysfunctions or are at the extremes of age. More data are required in the field of pain management, particularly with regard to renal and hepatic dysfunction. In turn, these data serve as a foundation for physicians making practice decisions based on current evidence. Until this is achieved, clinicians must rely on anecdotal evidence and the experiences of others to treat a complex issue: pain.

A structured literature review of pain assessment and management of patients with chronic kidney disease

AIMS AND OBJECTIVES

This paper reviews the literature concerning nurses' assessment and management of pain in adult patients with chronic kidney disease, and proposes implications for clinical practice to support the control of pain in these patients.

BACKGROUND

Chronic kidney disease is a worldwide public health concern with increasing incidence and prevalence, poor patient outcomes and high cost. Patients with kidney disease often experience pain. Optimal pain assessment and management are key clinical activities; however, inadequate pain control by health professionals persists. Renal failure compounds this problem because of the small margin between pain relief and toxicity, and the patient's concomitant health problems.

CONCLUSIONS

The literature review uses 93 articles that were published in medical- and other health-related journals, including 12 medical and pharmaceutical studies specifically relating to pain control in adults with kidney disease. Very little research has been conducted on pain in patients with kidney disease prior to requiring dialysis or kidney transplantation for survival. However, past research showed pain is common and analgesics are underprescribed in patients on dialysis in end-stage kidney disease. The review indicates that an interest in nephrotoxicity and analgesic-induced morbidity dominates over an interest in pain relief in patients with kidney disease. Most analgesics are excreted renally or by the liver, and the use of simple analgesics such as paracetamol is cautioned.

RELEVANCE TO CLINICAL PRACTICE

Findings from the literature review highlight specific difficulties relating to effective pain control in patients with chronic kidney disease. Research is required to identify and overcome barriers to effective pain management, including the development of specific tools to facilitate interventions that optimize analgesic outcomes in patients with chronic kidney disease.

[Use of opioid analgesics in diagnosis and decision-making in patients with acute nontraumatic abdominal pain. A systematic review of the literature]

INTRODUCTION

The use of analgesics during the diagnosis and decision-making process in patients with acute nontraumatic abdominal pain is controversial. The aim of the present study was to determine whether the use of opioid analgesics in patients with acute nontraumatic abdominal pain increases the risk of diagnostic error.

METHOD

We performed a systematic review of the literature. Randomized clinical trials (RTCs) comparing the use of opioid analgesics with placebo administered before any procedure in patients with acute nontraumatic abdominal pain were included. There was no restriction on language. RTCs unrelated to this subject were excluded. The variables analyzed were age, gender, and the percentage of adverse effects, appendicitis, changes on physical examination and diagnostic error, modification of pain severity measured by a visual analog scale, and methodological quality of the studies. A search was performed in the MEDLINE and Cochrane databases, using MeSH terms. Each article was analyzed by applying a methodological quality score through which weighted means were applied for each variable. The Chi-square and Student's t-test were applied to compare the groups.

RESULTS

Six articles meeting the selection criteria were found. The mean methodological quality score was 21.6 points. The studies represented a population of 363 patients treated with opioids and 336 patients treated with placebo. There were no differences in the mean age of the patients (39.4 vs 39.6 years), distribution by gender, prevalence of acute appendicitis (23.3% vs 24%) or diagnostic error (15.6% vs 21.1%; p = 0.0637). Differences were found in the variable of pain reduction (27.2 vs 7.2 mm, respectively; p = 0.0167).

CONCLUSIONS

The use of opioid analgesics in patients with acute nontraumatic abdominal pain does not increase the risk of diagnostic error and reduces pain during the decision-making process.

Glucuronidation in therapeutic drug monitoring

BACKGROUND

Glucuronidation is a major drug-metabolizing reaction in humans. A pharmacological effect of glucuronide metabolites is frequently neglected and the value of therapeutic drug monitoring has been questioned. However, this may not always be true.

METHODS

In this review the impact of glucuronidation on therapeutic drug monitoring has been evaluated on the basis of a literature search and experience from the own laboratory.

RESULTS

The potential role of monitoring glucuronide metabolite concentrations to optimize therapeutic outcome is addressed on the basis of selected examples of drugs which are metabolized to biologically active/reactive glucuronides. Furthermore indirect effects of glucuronide metabolites on parent drug pharmacokinetics are presented. In addition, factors that may modulate the disposition of these metabolites (e.g. genetic polymorphisms, disease processes, age, and drug-drug interactions) are briefly mentioned and their relevance for the clinical situation is critically discussed.

CONCLUSION

Glucuronide metabolites can have indirect as well as direct pharmacological or toxicological effects. Although convincing evidence to support the introduction of glucuronide monitoring into clinical practice is currently missing, measurement of glucuronide concentrations may be advantageous in specific situations. If the glucuronide metabolite has an indirect effect on the pharmacokinetics of the parent compound, monitoring of the parent drug may be considered. Furthermore pharmacogenetic approaches considering uridine diphosphate (UDP) glucuronosyltransferases polymorphisms may become useful in the future to optimize therapy with drugs subject to glucuronidation.

Effect of repeated administrations of heroin, naltrexone, methadone, and alcohol on morphine glucuronidation in the rat

RATIONALE

Heroin is rapidly metabolized to morphine that in turn is transformed in morphine-3-glucuronide (M3G), an inactive metabolite, and morphine-6-glucuronide (M6G), a potent mu-opioid receptor (MOR) agonist. We have found that heroin addicts exhibit higher M6G/M3G ratios relative to morphine-treated control subjects. We have also shown that heroin-treated rats exhibit measurable levels of M6G (which is usually undetectable in this species) and reduced levels of M3G.

OBJECTIVE

We investigated the role of MOR in these effects of heroin, by examining the effects of methadone, a MOR agonist, and of naltrexone, a MOR antagonist, on morphine glucuronidation. We also investigated the effects of alcohol, which is known to alter drug metabolism and is frequently coabused by heroin addicts.

METHODS

Morphine glucuronidation was studied in liver microsomes obtained from rats exposed daily for 10 days to saline, heroin (10 mg/kg, i.p.), naltrexone (20-40 mg/kg, i.p.), heroin + naltrexone (10 mg/kg+20-40 mg/kg, i.p.), methadone (5-20 mg/kg, i.p.), or 10% ethanol.

RESULTS

Heroin induced the synthesis of M6G and decreased the synthesis of M3G. Naltrexone exhibited intrinsic modulatory activity on morphine glucuronidation, increasing the synthesis of M3G via a low-affinity/high-capacity reaction characterized by positive cooperativity. The rate of M3G synthesis in the heroin + naltrexone groups was not different from that of the naltrexone groups. Methadone and ethanol induced a modest increase in M3G synthesis and had no effect on M6G synthesis.

CONCLUSION

The effects of heroin on morphine glucuronidation are not shared by methadone or alcohol (two drugs that figure prominently in the natural history of heroin addiction) and do not appear to depend on the activation of MOR.

Opioids in renal failure and dialysis patients

This article reviews the literature pertaining to the metabolism of several of the commonly used opioids, and the known activity of their metabolites. The effect of renal failure on the pharmacokinetics of these drugs and metabolites is then reviewed. Finally, the effect of renal dialysis on opioid drugs and metabolites is reviewed. Based on the review, it is recommended that morphine and codeine are avoided in renal failure/dialysis patients; hydromorphone or oxycodone are used with caution and close monitoring; and that methadone and fentanyl/sufentanil appear to be safe to use. Note is made that the "safe" drugs in renal failure are also the least dialyzable.

Analgesic prescription patterns among hemodialysis patients in the DOPPS: Potential for underprescription

BACKGROUND

Dialysis patients require special consideration regarding analgesics, given their altered pharmacokinetic and pharmacodynamic profiles and increased potential for adverse reactions.

METHODS

Analgesic prescription patterns were investigated using data from the Dialysis Outcomes and Practice Patterns Study (DOPPS), with 3749 patients in 142 United States facilities studied between May 1996 and September 2001.

RESULTS

The proportion of patients prescribed any analgesic decreased from 30.2% to 24.3%; narcotic prescriptions decreased from 18.0% to 14.9%. The most commonly prescribed narcotics were propoxyphene/acetaminophen combinations (47.2%). Combinations containing acetaminophen were prescribed concurrently for 84.1% of patients on narcotics. About one half of prescriptions for narcotics, acetaminophen, and cyclooxygenase-2 (COX-2) agents were for 12 months or more; one half of prescriptions for nonsteroidal anti-inflammatory drugs (NSAIDs) were for 8 months or more. The proportion of patients prescribed analgesics varied by facility (mean +/- SD = 27.9%+/- 18.9% for all analgesics, range 0% to 89.3%). Analgesic prescription was more likely among the elderly, women, and patients with cardiovascular disease (other than coronary artery disease or congestive heart failure), lung and psychiatric disease, cancer (other than skin), and recurrent cellulitis. Patients prescribed laxatives were almost twice as likely to be on a narcotic (odds ratio = 1.95, P < 0.0001). Analgesic prescription did not correlate with loss of residual renal function or hospitalization for a gastrointestinal disorder. Three-quarters of patients reporting moderate to very severe pain were not prescribed analgesics. Furthermore, 74% of patients with pain that interfered with work had no analgesic prescription.

CONCLUSION

Dialysis patients and providers may benefit from both refinement of existing guidelines and a renewed understanding regarding appropriate prescription of analgesics.

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.

Opioid and non-opioid analgesics

Opioids are the most potent analgesics. Toxicity results either from effects mediated by variation in affinity and intrinsic efficacy at specific opioid receptors or, rarely, from a direct toxic effect of the drugs. For some adverse effects, opioids exhibit a 'dual pharmacology' whereby these effects are usually observed only in pain-free individuals, and are not seen in patients in pain. Paracetamol, although generally very safe in therapeutic doses, displays potentially fatal toxicity in overdose requiring specific treatment. Non-steroidal anti-inflammatory drugs (NSAIDs) are known to act by inhibiting COX-1 and COX-2 isoenzymes to various degrees. Toxicity arises primarily from undesired inhibition at these enzyme sites. Knowledge of the mechanism of action of these drugs is fundamental to the understanding of their potential for toxicity, the details of which are still emerging.

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.

Contribution of morphine-6-glucuronide to antinociception following intravenous administration of morphine to healthy volunteers

This study was performed to develop an integrated pharmacokinetic-pharmacodynamic model for estimating the contribution of morphine-6-glucuronide (M6G) to morphine-associated antinociception in humans. Healthy volunteers (n = 8) received 10 mg of morphine sulfate as a 5-minute i.v. infusion. A Contact Thermode heat probe was placed on the volar forearm to elicitpain. Thermal threshold, defined as the temperature at which pain was first perceived, was measured at fixed time intervals over 8 hours. Serum concentrations of morphine and M6G were determined by LC/MS. Concentration- and effect-time data were analyzed by stepwise nonlinear least-squares regression. The pharmacodynamic parameter estimates were recovered with a linear effect-compartment model and were used to assess the contribution of M6G to morphine-associated analgesia. The estimates (mean +/- SEM) for morphine total clearance and steady-state volume of distribution were 1.0 +/- 0.07 L/h/kg and 1.6 +/- 0.1 L/kg, respectively. The AUC ratio of M6G to morphine was 0.73 +/- 0.06. The contribution of M6G to analgesia ranged from < 0.1% to 66% and was inversely related to the overall effect elicited by the morphine dose (r2 = 0.776). Differences in gender were observed where the contribution (mean +/- SEM) of M6G to analgesia was 32% +/- 19% in males (n = 3) and 13% +/- 8% in females (n = 5). These results suggest that as the overall effect of morphine increases, the fractional contribution of M6G declines and the contribution of M6G to analgesia may differ between males and females. Alterations in the M6G/morphine system may have clinically significant pharmacodynamic consequences.

Morphine-6-glucuronide: an analgesic of the future?

Morphine-6-beta-glucuronide (M6G) is an opioid agonist that plays a role in the clinical effects of morphine. Although M6G probably crosses the blood-brain barrier with difficulty, during long term morphine administration it may reach sufficiently high CNS concentrations to exert clinically relevant opioid effects. As a consequence of its almost exclusive renal elimination, M6G may accumulate in the body of patients with impaired renal function and cause severe opioid adverse effects with insidious onset and long persistence. Its profile of receptor affinities, however, gives reason to speculate that M6G may exhibit analgesic effects while causing fewer adverse effects than morphine. This is supported by reports of the good tolerability of intrathecal and intravenous injections of M6G in humans with intact renal function. M6G may thus be contemplated as an analgesic for short term postoperative analgesia, especially for intrathecal analgesic therapy. In addition, its possibly higher potency than morphine makes M6G a candidate opioid for local or peripheral analgesic therapy. However, current knowledge is too incomplete to finally judge the clinical usefulness of M6G. The next topics for clinical research on M6G should include: (i) a comparison of the potencies of M6G and morphine to cause wanted and unwanted clinical effects; (ii) development of a predictive population pharmacokinetic-pharmacodynamic model of M6G with calculation of the transfer half-life between plasma and effect site; and (iii) identification of cofactors influencing the action of M6G that can serve as predictors for the clinical outcome of morphine/M6G therapy in an individual including the pharmacogenetics of M6G.