Pharmacokinetics and pharmacodynamics of codeine in end-stage renal disease

Opioid Prescription in Patients With Chronic Kidney Disease: A Systematic Review of Comparing Safety and Efficacy of Opioid Use in Chronic Kidney Disease Patients

Patients with diminished renal function necessitate special care. In patients with chronic kidney disease (CKD), opioid analgesics should be prescribed based on the severity of renal insufficiency; this will determine treatment options at the beginning and throughout the management of pain in CKD patients. The dosage of hydrophilic drugs and drugs with active metabolites should be adjusted according to the severity of CKD, and the process of treatment should be monitored by modifying drug dosages as necessary for background and breakthrough pain. Patients with CKD may benefit from opioid analgesics that are lipophilic, such as methadone, fentanyl, and buprenorphine, as the first line; however, fentanyl is inappropriate for patients undergoing hemodialysis. Opioid prescription in CKD patients is the subject of this systematic review, which aims to compare their safety and efficacy. This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 recommendations. Using three databases (PubMed, ScienceDirect, and Google Scholar), we collected and reviewed articles, including literature reviews, randomized control trials (RCTs), and systematic reviews published between 1980 and 2022, to enable us to gather enough valuable data on this rare topic. After applying appropriate filters, a total of 109 results were obtained. They were further screened and subjected to quality assessment tools, which finally yielded 11 studies included in this systematic review. This consisted of two RCTs, two systematic reviews, and seven narrative reviews. This review focused on the safety and appropriate use of opioids in patients with CKD. The accumulation of morphine and codeine metabolites may result in neurotoxic side effects. Hydromorphone and oxycodone are considered safe to administer but require careful adjustments in dosage. Common comorbidities among patients with CKD may amplify opioid-related adverse effects.

Opioids for chronic pain management in patients with dialysis-dependent kidney failure

Chronic pain is highly prevalent among adults treated with maintenance haemodialysis (HD) and has profound negative effects. Over four decades, research has demonstrated that 50-80% of adult patients treated with HD report having pain. Half of patients with HD-dependent kidney failure (HDKF) have chronic moderate-to-severe pain, which is similar to the burden of pain in patients with cancer. However, pain management in patients with HDKF is often ineffective as most patients report that their pain is inadequately treated. Opioid analgesics are prescribed more frequently for patients receiving HD than for individuals in the general population with chronic pain, and are associated with increased morbidity, mortality and health-care resource use. Furthermore, current opioid prescribing patterns are frequently inconsistent with guideline-recommended care. Evidence for the effectiveness of opioids in pain management in general, and in patients with HDKF specifically, is lacking. Nonetheless, long-term opioid therapy has a role in the treatment of some patients when used selectively, carefully and combined with an ongoing assessment of risks and benefits. Here, we provide a comprehensive overview of the use of opioid therapy in patients with HDKF and chronic pain, including a discussion of buprenorphine, which has potential as an analgesic option for patients receiving HD owing to its unique pharmacological properties.

Narcotic Use for Acute Postoperative Pain Management in Mohs Micrographic Surgery Patients With End Stage Renal Disease: A Review of the Literature

BACKGROUND

Uncontrolled acute postoperative pain presents a significant management challenge when opioids are used in patients with end-stage renal disease (ESRD). Currently, there is a lack of quality pharmacokinetic and pharmacodynamic data regarding opioid medication use in ESRD patients to optimize safe and effective management.

OBJECTIVE

To review the published literature on pharmacologic evidence for and against the use of opioid medications for acute postoperative pain following Mohs micrographic surgery in ESRD patients.

METHODS

A search of PubMed was conducted to identify articles on the pharmacokinetic and pharmacodynamic properties of opioid pain medications in ESRD patients through March 1, 2020.

RESULTS

Seventy-five articles were reviewed. Limited data exist on opioids safe for use in ESRD and are mostly confined to small case series. Studies suggest tramadol and hydromorphone could be considered when indicated. Methadone may be a safe option, but should be reserved for treatment coordinated by a trained pain subspecialist.

CONCLUSION

Randomized clinical trials are lacking. Studies that are available are not sufficient to perform a quantitative methodologic approach. Evidence supports the judicious use of postoperative opioid medications in ESRD patients at the lowest possible dose to achieve clinically meaningful improvement in pain and function.

Safe Use of Opioids in Chronic Kidney Disease and Hemodialysis Patients: Tips and Tricks for Non-Pain Specialists

In patients suffering from moderate-to-severe chronic kidney disease (CKD) or end-stage renal disease (ESRD), subjected to hemodialysis (HD), pain is very common, but often underestimated. Opioids are still the mainstay of severe chronic pain management; however, their prescription in CKD and HD patients is still significantly low and pain is often under-treated. Altered pharmacokinetics and the lack of clinical trials on the use of opioids in patients with renal impairment increase physicians' concerns in this specific population. This narrative review focused on the correct and safe use of opioids in patients with CKD and HD. Morphine and codeine are not recommended, because the accumulation of their metabolites may cause neurotoxic symptoms. Oxycodone and hydromorphone can be safely used, but adequate dosage adjustments are required in CKD. In dialyzed patients, these opioids should be considered as second-line agents and patients should be carefully monitored. According to different studies, buprenorphine and fentanyl could be considered first-line opioids in the management of pain in CKD; however, fentanyl is not appropriate in patients undergoing HD. Tapentadol does not need dosage adjustment in mild-to-moderate renal impairment conditions; however, no data are available on its use in ESRD. Opioid-related side effects may be exacerbated by common comorbidities in CKD patients. Opioid-induced constipation can be managed with peripherally-acting-μ-opioid-receptor-antagonists (PAMORA). Unlike the other PAMORA, naldemedine does not require any dose adjustment in CKD and HD patients. Accurate pain diagnosis, opioid titration and tailoring are mandatory to minimize the risks and to improve the outcome of the analgesic therapy.

Opioid Safety and Concomitant Benzodiazepine Use in End-Stage Renal Disease Patients

Background

Opioid use is common in end-stage renal disease (ESRD) patients. However, safety of individual opioids and concomitant benzodiazepine use has not been studied.

Objective

To study the epidemiology of opioid and concomitant benzodiazepine use in ESRD population. To study the clinical safety profile of individual opioids in patients on hemodialysis.

Design

Retrospective analysis of the U.S. Renal Data System. A comprehensive review of the current literature was performed to update currently used opioid safety classification.

Participants

ESRD patients ≥18 years on hemodialysis who were enrolled in Medicare A and B and Part D between 2006 and 2012, excluding those with malignancy.

Main Measures

Hospital admission with diagnosis of prescription opioid overdose within 30, 60, and 90 days of prescription; death due to opioid overdose.

Results

Annually, the percentage of patients prescribed any opioid was 52.2%. Overall trend has been increasing except for a small dip in 2011, despite which the admissions due to opioid overdose have been rising. 30% of those who got a prescription for opioids also got a benzodiazepine prescription. 56.5% of these patients received both prescriptions within a week of each other. Benzodiazepine use increased the odds of being on opioids by 3.27 (CI 3.21–3.32) and increased the odds of hospitalization by 50%. Opioids considered safe such as fentanyl and methadone were associated with 3 and 6 folds higher odds of hospitalization within 30 days of prescription. Hydrocodone had the lowest odds ratio (1.9, CI 1.8–2.0).

Conclusions

Concurrent benzodiazepine use is common and associated with higher risk of hospitalization due to opioid overdose. Possible opioid-associated hospital admission rate is 4-5 times bigger in ESRD population than general population. Current safety classification of opioids in these patients is misleading, and even drugs considered safe based on pharmacokinetic data are associated with moderate to very high risk of hospitalization. We propose a risk-stratified classification of opioids and suggest starting to use them in all ESRD patients.

Associations of Opioid Prescriptions with Death and Hospitalization across the Spectrum of Estimated GFR

BACKGROUND AND OBJECTIVES

Most opioids undergo kidney excretion. The goal of this study was to evaluate opioid-associated risks of death and hospitalization across the range of eGFR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study population included adult primary care patients in Geisinger Health (Danville, PA) between 2008 and 2017. People receiving their first opioid prescription were propensity matched to people receiving NSAIDS (and, in sensitivity analysis, gabapentinoids) and the risk of death and hospitalization were compared, classifying opioid medication exposure as time-varying daily oral morphine milligram equivalents (MMEs) across time-varying eGFR.

RESULTS

The propensity-matched cohort included 46,246 patients prescribed either opioids or NSAIDs between 2008 and 2017 (mean [SD] age, 54 [16] years; 56% female; 3% of black race). Prescriptions for 1-59 and ≥60 MMEs were associated with higher risk of death (HR, 1.70; 95% CI, 1.41 to 2.05 for 1-59 MMEs; HR, 2.25; 95% CI, 1.82 to 2.79 for ≥60 MMEs) and hospitalization (HR, 1.38; 95% CI, 1.30 to 1.46 for 1-59 MMEs; HR, 1.68; 95% CI, 1.56 to 1.81 for ≥60 MMEs) compared with NSAID prescriptions, when evaluated at eGFR 80 ml/min per 1.73 m². The relative risk of death associated with ≥60 MMEs was higher at lower GFR (e.g., eGFR, 40 ml/min per 1.73 m²; HR, 3.94; 95% CI, 2.70 to 5.75; P for interaction, 0.01). When gabapentinoids were used as the comparison medication, only ≥60 MMEs were significantly associated with higher risk of death (HR, 2.72; 95% CI, 1.71 to 4.34), although both 1-59 and ≥60 MMEs were associated with risk of hospitalization (HR, 1.22; 95% CI, 1.04 to 1.43 for 1-59 MMEs; HR, 1.54; 95% CI, 1.28 to 1.86 for ≥60 MMEs).

CONCLUSIONS

The receipt of prescription opioids was associated with a higher risk of death and hospitalization compared with other pain medications, particularly with higher doses and at lower eGFR.

Pain Management in Pediatric Chronic Kidney Disease

Pain is a common problem in children with chronic kidney disease (CKD); however, limited data exist regarding its management. Although most pain is managed pharmacologically, in some instances non-pharmacologic management can aid in safely ameliorating discomfort. Because of the accumulation of toxic metabolites, many common pain medications have adverse effects on kidney function or altered pharmacokinetics in the setting of CKD. Decreased clearance impacts safe dosing of analgesics. The pain management of patients on renal replacement therapy requires an understanding of drug clearance due to the different modalities of dialysis. This educational review highlights pain medications that are safe, albeit often with adjusted dosing, as well as drugs best avoided in the management of pediatric kidney disease. Acetaminophen should be used as a first-line therapy for pain management in children with CKD. Opioids may be added to control moderate to severe pain. Although data are currently lacking, buprenorphine holds promise as a potentially useful drug for the treatment of pain in pediatric patients with CKD. The addition of adjuvant pain medications and non-pharmacologic therapies maybe also be helpful. Despite these options, pain often remains difficult to treat in children with CKD.

Emergency medicine evaluation and management of the end stage renal disease patient

BACKGROUND

End stage renal disease (ESRD) is increasing in the U.S., and these patients demonstrate greater all-cause mortality, cardiovascular events, and hospitalization rates when compared to those with normal renal function. These patients may experience significant complications associated with loss of renal function and dialysis.

OBJECTIVE

This review evaluates complications of ESRD including cardiopulmonary, neurologic, infectious disease, vascular, and access site complications, as well as medication use in this population.

DISCUSSION

ESRD incidence is rapidly increasing, and patients commonly require renal replacement therapy including hemodialysis (HDS) or peritoneal dialysis (PD), each type with specific features. These patients possess greater risk of neurologic complications, cardiopulmonary pathology, infection, and access site complications. Focused history and physical examination are essential. Neurologic issues include uremic encephalopathy, cerebrovascular pathology, and several others. Cardiopulmonary complications include pericarditis, pericardial effusion/tamponade, acute coronary syndrome, sudden cardiac death, electrolyte abnormalities, pulmonary edema, and air embolism. Infections are common, with patients more commonly presenting in atypical fashion. Access site infections and metastatic infections must be treated aggressively. Access site complications include bleeding, aneurysm/pseudoaneurysm, thrombosis/stenosis, and arterial steal syndrome. Specific medication considerations are required for analgesics, sedatives, neuromuscular blocking agents, antimicrobials, and anticoagulants.

CONCLUSIONS

Consideration of renal physiology with complications in ESRD can assist emergency providers in the evaluation and management of these patients. ESRD affects many organ systems, and specific pharmacologic considerations are required.

The Role of the Kidney in Drug Elimination: Transport, Metabolism, and the Impact of Kidney Disease on Drug Clearance

Recent advances in the identification and characterization of renal drug transporters and drug-metabolizing enzymes has led to greater understanding of their roles in drug and chemical elimination and in modulation of the intrarenal exposure and response to drugs, nephrotoxic compounds, and physiological mediators. Furthermore, there is increasing awareness of the potential importance of drug-drug interactions (DDIs) arising from inhibition of renal transporters, and regulatory agencies now provide recommendations for the evaluation of transporter-mediated DDIs. Apart from the well-recognized effects of kidney disease on renal drug clearance, there is a growing body of evidence demonstrating that the nonrenal clearances of drugs eliminated by certain transporters and drug-metabolizing enzymes are decreased in patients with chronic kidney disease (CKD). Based on these observations, renal impairment guidance documents of regulatory agencies recommend pharmacokinetic characterization of both renally cleared and nonrenally cleared drugs in CKD patients to inform possible dosage adjustment.

Drug Dosing in Critically Ill Patients with Renal Failure: A Pharmacokinetic Approach

Accurate pharmacotherapy management in the intensive care unit (ICU) patient is crucial to minimize adverse drug events. Pharmacokinetic principles including absorption, distribution, metabolism, and excretion (ADME) all play an important role in determining the fate of medications used in the critical care setting. Renal failure in this setting further alters pharmacokinetic parameters, resulting in drug dosing changes. This article highlights and applies principles of drug dosing in normal patients and in the pharmacokinetically challenging environment of critically ill patients with renal failure. Specific drug dosing tables serve as a guide for the clinician to renally adjust medication doses in the critically ill patient with renal failure.

Pain relief management following proximal femoral fractures: Options, issues and controversies

The majority of proximal femoral fractures occur in the elderly population. Safe and adequate pain relief is an integral part of the overall management of hip fractures. Inherent difficulties in the assessment of pain in elderly need to be taken into account and unique considerations should be made regarding the effective analgesia due to different elderly physiology, and their response to trauma and subsequent surgery. The pain management should start as soon as possible and special emphasis should be paid to contemporary methods of regional anaesthesia whilst a multimodal approach should be adopted in the perioperative period. The present review summarises the contemporary treatment options and controversies pertaining to the management of pain in elderly patients with proximal femoral fractures.

An Approach to Pain Management in End Stage Renal Disease: Considerations for General Management and Intradialytic Symptoms

The prevalence and severity of symptoms in patients with advanced chronic kidney disease is higher than those of the general population and comparable to those with other chronic and serious medical conditions. Despite the prevalence and severity in this population, symptoms continue to be under-recognized and inadequately managed. The recognition of specific intradialytic pain syndromes such as pain related to arteriovenous access, headaches, muscle cramps or generalized pain by providers may aid in improving patient compliance and quality of life. The approach to pain management in end stage renal disease patients follows that of the general population with specific considerations regarding clearance and potential side effects guiding selection of agents. Overall, evidence is limited regarding the pharmacology of many medications in this population.

Pain in chronic kidney disease: a scoping review

There is increasing international attention in efforts to integrate palliative care principles, including pain and symptom management, into the care of patients with advanced chronic kidney disease (CKD). The purpose of this scoping review was to determine the extent, range, and nature of research activity around pain in CKD with the goal of (i) identifying gaps in current research knowledge; (ii) guiding future research; and (iii) creating a rich database of literature to serve as a foundation of more detailed reviews in areas where the data are sufficient. This review will specifically address the epidemiology of pain in CKD, analgesic use, pharmacokinetic data of analgesics, and the management of pain in CKD. It will also capture the aspects that pertain to specific pain syndromes in CKD such as peripheral neuropathy, carpal tunnel syndrome, joint pain, and autosomal dominant polycystic kidney disease.

Mitigating the risk of opioid abuse through a balanced undergraduate pain medicine curriculum

Chronic pain is highly prevalent in the United States and Canada, occurring in an estimated 30% of the adult population. Despite its high prevalence, US and Canadian medical schools provide very little training in pain management, including training in the safe and effective use of potent analgesics, most notably opioids. In 2005, the International Association for the Study of Pain published recommendations for a core undergraduate pain management curriculum, and several universities have implemented pilot programs based on this curriculum. However, when outcomes have been formally assessed, these initiatives have resulted in only modest improvements in physician knowledge about chronic pain and its treatment. This article discusses strategies to improve undergraduate pain management curricula and proposes areas in which those efforts can be augmented. Emphasis is placed on opioids, which have great potency as analgesics but also substantial risks in terms of adverse events and the risk of abuse and addiction. The authors conclude that the most important element of an undergraduate pain curriculum is clinical experience under mentors who are capable of reinforcing didactic learning by modeling best practices.

Options for treating postherpetic neuralgia in the medically complicated patient

Patients with postherpetic neuralgia (PHN) are often of advanced age or immunocompromised and likely to have ≥1 comorbid medical condition for which they receive ≥1 medication (polypharmacy). Comorbidities affecting renal or hepatic function can alter pharmacokinetics, thereby impacting the efficacy or tolerability of PHN analgesic therapies. Cardiovascular, cerebrovascular, or psychiatric comorbidities may increase patient vulnerability to potential adverse events associated with some PHN analgesic therapies. Because PHN is a localized condition, localized therapy with a topical analgesic (lidocaine patch 5% and capsaicin 8% patch or cream) may provide adequate efficacy while mitigating the risk of systemic adverse events compared with oral analgesics (eg, tricyclic antidepressants, anticonvulsants, opioids). However, combined therapy with a topical and an oral analgesic or with >1 oral analgesic may be needed for optimal pain management in some patients. This review summarizes how comorbidities and concomitant medications should be taken into account when selecting among available pharmacotherapies for PHN and provides recommendations for the selection of therapies that will provide analgesia while minimizing the risk of adverse events.

Update on prescription extended-release opioids and appropriate patient selection

Chronic pain is largely underdiagnosed, often undertreated, and expected to increase as the American population ages. Many patients with chronic pain require long-term treatment with analgesic medications, and pain management may involve use of prescription opioids for patients whose pain is inadequately controlled through other therapies. Yet because of the potential for abuse and addiction, many clinicians hesitate to treat their patients with pain with potentially beneficial agents. Finding the right opioid for the right patient is the first - often complicated - step. Ensuring that patients continue to properly use the medication while achieving therapeutic analgesic effects is the long-term goal. Combined with careful patient selection and ongoing monitoring, new formulations using extended-release technologies incorporating tamper-resistant features may help combat the growing risk of abuse or misuse, which will hopefully reduce individual suffering and the societal burden of chronic pain. The objective of this manuscript is to provide an update on extended-release opioids and to provide clinicians with a greater understanding of which patients might benefit from these new opioid formulations and how to integrate the recommended monitoring for abuse potential into clinical practice.

Methadone, codeine and acute haemorrhagic necrotising pancreatitis: which came first?

Acute haemorrhagic necrotising pancreatitis lead to the death at home of a young female who was on a methadone maintenance programme. Toxic levels of codeine with potentially lethal levels of methadone and morphine were found at post-mortem. Whether opiates caused the pancreatitis or were the consequence of self-medication for pain is impossible to differentiate. Forensic toxicology may pose the question but be unable to provide the answer.

Management of acute and post-operative pain in chronic kidney disease

Chronic kidney disease is common and patients with many co-morbid conditions frequently have to undergo surgical procedures and, therefore, require effective pain management. The pharmacokinetics of various analgesic agents are not well studied in patients with chronic kidney disease and the risk of accumulation of the main drug or their metabolites, resulting in serious adverse events, is a common scenario on medical and surgical wards. It is common for these patients to be cared for by 'non-nephrologists' who often prescribe the standard dose of the commonly used analgesics, without taking into consideration the patient's kidney function. It is important to recognize the problems and complications associated with the use of standard doses of analgesics, and highlight the importance of adjusting analgesic dosage based on kidney function to avoid complications while still providing adequate pain relief.

Management of acute and post-operative pain in chronic kidney disease

Chronic kidney disease is common and patients with many co-morbid conditions frequently have to undergo surgical procedures and, therefore, require effective pain management. The pharmacokinetics of various analgesic agents are not well studied in patients with chronic kidney disease and the risk of accumulation of the main drug or their metabolites, resulting in serious adverse events, is a common scenario on medical and surgical wards. It is common for these patients to be cared for by 'non-nephrologists' who often prescribe the standard dose of the commonly used analgesics, without taking into consideration the patient's kidney function. It is important to recognize the problems and complications associated with the use of standard doses of analgesics, and highlight the importance of adjusting analgesic dosage based on kidney function to avoid complications while still providing adequate pain relief.

Effects of intermittent hemodialysis on buprenorphine and norbuprenorphine plasma concentrations in chronic pain patients treated with transdermal buprenorphine

The present study was designed to study the impact of intermittent hemodialysis on the disposition of the partial agonist buprenorphine and its metabolite norbuprenorphine during therapy with transdermal buprenorphine in chronic pain patients with end-stage kidney disease. Ten patients (mean age 63 years) who had received transdermal buprenorphine for at least 1 week, were asked to provide blood samples immediately before and after hemodialysis. Blood samples were analysed for buprenorphine and its metabolite norbuprenorphine. The median buprenorphine plasma concentrations were found to be 0.16 ng/ml before and 0.23 ng/ml after hemodialysis. A significant correlation between plasma levels and administered doses was observed (Spearman R=0.74; P<0.05). In three patients norbuprenorphine plasma levels were detected. No differences in pain relief before and after hemodialysis were observed. This investigation shows no elevated buprenorphine and norbuprenorphine plasma levels in patients with renal insufficiency receiving transdermal buprenorphine up to 70 microg/h. Furthermore, hemodialysis did not affect buprenorphine plasma levels, leading to stable analgesic effects during the therapy.

Management of the dialysis patient in general intensive care

The incidence of end-stage renal disease (ESRD) is rising and represents an important group of patients admitted to intensive care units (ICU). ESRD patients have significant co-morbidities and specific medical requirements. Renal replacement therapy (RRT), cardiovascular disease, disorders of electrolytes, drug metabolism, and sepsis are discussed. This review provides a practical approach to problems specific to the ESRD patient and common problems on ICU that require special consideration in ESRD patients. ESRD patients are at risk of hyperkalaemia. I.V. insulin and nebulized salbutamol lower serum potassium until definitive treatment with RRT is instituted. ESRD patients are prone to hypocalcaemia, which requires i.v. replacement if associated with complications. Midazolam has delayed metabolism and elimination in renal impairment and should be avoided. Morphine and its derivatives accumulate in renal failure and shorter-acting opiates are preferable. The use of diuretics is limited to patients with residual urine output. When required, therapeutic systemic anticoagulation should be achieved with unfractionated heparin as it is reversible and its metabolism and clearance are independent of renal function. The risk of sepsis is higher among ESRD patients when compared with patients with normal renal function. Empiric treatment should include both Gram-positive and Gram-negative cover, and methicillin-resistant Staphylococcus aureus cover if the patient has a dialysis catheter. Cardiovascular events account for the majority of deaths among ESRD patients. Troponin-I and CK-MB in combination should be used as markers of acute myocardial damage in the appropriate context, whereas B-type natriuretic peptide and troponin-T values are of less value.

Pain in chronic kidney disease: prevalence, cause and management

Pain is an unpleasant sensory and emotional experience and is the most common symptom experienced by renal patients. It can be caused by primary co-morbid diseases, renal replacement therapies, medication or treatment side effects, and its intensity varies from moderate to severe. Pain management in renal patients is difficult, since the distance between pain relief and toxicity is very small. This paper will provide an algorithm for pain management proposed using paracetamol, nonsteroid anti-inflamatory drugs (NSAIDs), mild and stronger opioids as well as complementary techniques. Quality of Life (QoL) and overall enhancement of the patient experience through better pain management are also discussed. To improve pain management it is essential that nurses recognise that they have direct responsibilities related to pain assessment and tailoring of opioid analgesics and better and more detailed education.

Rationalization and prediction of in vivo metabolite exposures: the role of metabolite kinetics, clearance predictions and in vitro parameters

IMPORTANCE OF THE FIELD

Due to growing concerns over toxic or active metabolites, significant efforts have been focused on qualitative identification of potential in vivo metabolites from in vitro data. However, limited tools are available to quantitatively predict their human exposures.

AREAS COVERED IN THIS REVIEW

Theory of clearance predictions and metabolite kinetics is reviewed together with supporting experimental data. In vitro and in vivo data of known circulating metabolites and their parent drugs were collected and the predictions of in vivo exposures of the metabolites were evaluated.

WHAT THE READER WILL GAIN

The theory and data reviewed will be useful in early identification of human metabolites that will circulate at significant levels in vivo and help in designing in vivo studies that focus on characterization of metabolites. It will also assist in rationalization of metabolite-to-parent ratios used as markers of specific enzyme activity.

TAKE HOME MESSAGE

The relative importance of a metabolite in comparison to the parent compound as well as other metabolites in vivo can only be predicted using the metabolite's in vitro formation and elimination clearances, and the in vivo disposition of a metabolite can only be rationalized when the elimination pathways of that metabolite are known.

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.

Clinical cases in acute intoxication

Over 2.5 million accidental and intentional drug-related poisonings are reported annually in the United States. Early diagnosis and management of patients who present with acute intoxication can significantly reduce both morbidity and mortality. The initial evaluation of patients with suspected or proven intoxications should focus on hemodynamic stability, mental status, and respiratory function. However, early recognition of toxic ingestion is paramount to implementing life-saving treatments. Important historical clues are often found in a social history that considers intravenous drug use, alcohol use, and any access or exposure to illicit substances. A patient's medication list should also be scrutinized for psychoactive or sedative medications, such as tricyclic antidepressants or opioids. In this article we present case-based discussions of the specific diagnosis and management of 5 commonly occurring acute intoxication syndromes.

Influence of the CYP2D6 polymorphism and hemodialysis on codeine disposition in patients with end-stage renal disease

OBJECTIVE

We studied the influence of three factors on drug disposition: genetic polymorphism, impaired renal excretion of drug metabolites, and the possible elimination by hemodialysis (HD), using codeine as a model drug.

METHODS

Based on the genotyping of three CYP2D6 polymorphisms in 228 HD patients, nine extensive metabolizers (EMs) and two poor metabolizers (PMs) were given a single oral dose of 50 mg codeine phosphate. Plasma concentrations of its metabolites codeine-6-glucuronide (C6G), morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) were determined after 2, 4, 6, 8 and 24 h (beginning of the HD session) and again after 4 h of HD (28 h). Codeine metabolites in plasma were quantitated by liquid chromatography-mass spectrometry (LC-MS).

RESULTS

The concentrations of C6G in plasma were high and similar in EMs and PMs. Two hours after the codeine intake, the mean concentration of M3G was 210 nM in EMs vs. 3.5 nM in PMs. The M6G metabolite concentrations could be quantitated in EMs but were below the limit of quantification in PMs (<1 nM). All three codeine metabolites/glucuronides remained unchanged or even increased until the start of HD, and thereafter, the concentrations decreased dramatically during the HD procedure.

CONCLUSIONS

Formation of the codeine metabolites M3G and M6G was dependent on the CYP2D6 genotype, as previously shown in healthy individuals. Elimination of glucuronides in these patients was absent until HD was performed. These factors need to be taken into consideration when drugs metabolized by CYPs are prescribed in HD patients.

Cancer pain and analgesia

Pain ranges in prevalence from 14-100% among cancer patients and occurs in 50-70% of those in active treatment. Cancer pain may result from direct invasion of tumor into nerves, bones, soft tissue, ligaments, and fascia, and may induce visceral pain through distension and obstruction. Cancer pain is multifaceted. Clinicians may describe cancer pain as acute, chronic, nociceptive (somatic), visceral, or neuropathic. Despite implementation of the WHO guidelines, reports of undertreatment of cancer pain persist in various clinical settings and in spite of decades of work to reduce unnecessary discomfort. Substantial obstacles to adequate pain relief with opioids include specific concerns of patients themselves, their family members, physicians, nurses, and the healthcare system. The WHO analgesic ladder serves as the mainstay of treatment for the relief of cancer pain in concert with tumoricidal, surgical, interventional, radiotherapeutic, psychological, and rehabilitative modalities. This multidimensional approach offers the greatest potential for maximizing analgesia and minimizing adverse effects. Primary therapies are directed at the source of the cancer pain and may enhance a patient's function, longevity, and comfort. Adjuvant therapies include nonopioids that confer analgesic effects in certain medical conditions but primarily treat conditions that do not involve pain. Nonopioid medications (over-the-counter agents) are useful in the management of mild to moderate pain, and their continuation through step 3 of the WHO ladder is an option after weighing a drug's risks and benefits in individual patients. Symptomatic treatment of severe cancer pain should begin with an opioid, regardless of the mechanism of the pain. They are very effective analgesics, titrate easily, and offer a favorable risk/benefit ratio. Cancer pain remains inadequately controlled despite the diagnostic and therapeutic means of ensuring that patients feel comfortable during their illness. Therefore, all practitioners need to make control of cancer pain a professional duty, even if they can only use the most basic and least expensive analgesic medications, such as morphine, codeine, and acetaminophen, to reduce human suffering.

Monitoring analgesia

Analgesia (pain relief) amnesia (loss of memory) and immobilisation are the three major components of anaesthesia. The perception of pain, and therefore, the need for analgesia, is individual, and the monitoring of analgesia is indirect and, in essence, of the moment. Under general anaesthesia, analgesia is continually influenced by external stimuli and the administration of analgesic drugs, and cannot be really separated from anaesthesia: the interaction between analgesia and anaesthesia is inescapable. Autonomic reactions, such as tachycardia, hypertension, sweating and lacrimation, although non-specific, are always regarded as signs of nociception or inadequate analgesia. Autonomic monitoring techniques, such as the analysis of heart rate variability, laser Doppler flowmetry, phlethysmographically derived indices and the pupillary light reflex, may help to quantitate reactions of the autonomic nervous system. For the past few years, automated electroencephalographic analysis has been of great interest in monitoring anaesthesia and could be useful in adapting the peroperative administration of opioids. A range of information collected from the electroencephalogram, haemodynamic readings and pulse plethysmography might be necessary for monitoring the level of nociception during anaesthesia. Information theory, multimodal monitoring, and signal processing and integration are the basis of future monitoring.

Measurements of plasma oxycodone, noroxycodone and oxymorphone levels in a patient with bilateral nephrectomy who is undergoing haemodialysis

The use of opioid analgesics in renal dysfunction is potentially problematic and many patients with end stage renal disease are unable to tolerate these medications. A greater understanding of the pharmacokinetics of opioid analgesics is vital in informing safe and effective practice. Using pharmacokinetic analysis, this case study demonstrates for the first time that oxycodone and its metabolites are removed by haemodialysis. As such, care should be taken when using oxycodone in patients undergoing haemodialysis.

Effects of renal diseases on the regulation and expression of renal and hepatic drug-metabolizing enzymes: a review

1. The activity of drug-metabolizing enzymes (DMEs) in extrahepatic organs is highest in the kidneys. Generally, the kidneys contain most, if not all, of the DMEs found in the liver. Surprisingly, some of these DMEs show higher activity in the kidneys than in the liver. 2. Most of the renal DMEs are localized in the cortex of the kidneys, especially in the proximal tubules. DMEs are also found in the distal tubules and collecting ducts. 3. Renal diseases such as acute and chronic renal failure and renal cell carcinoma alter the regulation of both hepatic and extrahepatic phase I and II DMEs. Changes in the expression of these DMEs seem to be tissue and species specific. 4. Generally, there is significant down-regulation of most of the phase I and a few of phase II DMEs at the protein, mRNA and activity levels. Unfortunately, the mechanisms leading to the alteration in DMEs in renal diseases remain unclear, although many theories have been made. 5. The presence of some circulating factors such as cytokines, nitric oxide, parathyroid hormones and increased intracellular calcium play a role in the regulation of DMEs in renal diseases.

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.

Probable codeine phosphate-induced seizures

OBJECTIVE

To report a case of seizure activity associated with oral codeine phosphate administered for analgesia in an elderly woman with end-stage renal disease.

CASE SUMMARY

A 73-year-old Taiwanese woman with end-stage renal disease received oral codeine phosphate 30 mg 4 times daily for her back and rib pain without adjustment of her dosage regimen. Seven days after starting codeine therapy, the woman became stuporous and developed tonic-clonic seizures. After phenytoin initiation, codeine discontinuation, and naloxone administration, the seizures did not recur.

DISCUSSION

Codeine is a frequently used opioid analgesic, especially when pain control with acetaminophen or nonsteroidal antiinflammatory drugs fails. Although seizures associated with codeine have been reported, pertinent data are very limited and the exact mechanism is unknown. An objective causality assessment indicated the seizure to be a probable drug-related event in this patient.

CONCLUSIONS

Elderly patients with end-stage renal disease may be predisposed to seizures with higher doses of codeine phosphate. It is imperative to adjust the codeine dosage regimen based on patients' renal function to avoid the potential toxicity with overdose.

Analgesia in patients with ESRD: a review of available evidence

Moderate to severe pain frequently accompanies chronic diseases in general and end-stage renal disease (ESRD) in particular. Several analgesic agents and associated metabolites show altered pharmacokinetics in the presence of reduced glomerular filtration rate. Drug-related side effects may exacerbate symptoms frequently observed in persons with chronic kidney disease (CKD; eg, fatigue, nausea, vomiting, and constipation) or those often attributed to hemodialysis therapy (eg, orthostatic hypotension and impaired cognition). Persons with advanced CKD and ESRD are at increased risk for adverse effects of analgesic agents because of enhanced drug sensitivity, comorbid conditions, and concurrent medication use. Dose adjustment and avoidance of certain analgesics may be required in patients with advanced CKD and ESRD. We review the available evidence on pharmacokinetics and adverse drug effects of various analgesic agents commonly used in patients with advanced CKD and ESRD. Determining an optimal approach to the control of pain in patients with advanced CKD and ESRD will require additional research.

Retrospective study of the use of hydromorphone in palliative care patients with normal and abnormal urea and creatinine

An uncontrolled retrospective study was conducted looking at the use of oral controlled-release hydromorphone in palliative care patients. Over a 2-year period 55 patients were switched to hydromorphone therapy, and the efficacy and outcomes were assessed. Urea and electrolyte measurements were also recorded at the time of opioid switch and renal impairment defined as urea > 10.5 mmol/l and/or creatinine > or = 101 mmol/l. This group of 29 patients with abnormal urea and/or creatinine (Group 1) was compared with the remaining 26 patients (Group 2) who had normal urea and creatinine. The major reasons for change to hydromorphone were side-effects (cognitive/drowsiness/nausea) on previous therapy. Following a switch to hydromorphone these side-effects improved in over 80% of patients (n = 55). Comparison between Group 1 and 2 demonstrated a significant difference in renal function but no significant differences in reasons for change, dose of opioids or response to change (over 80% improvement following opioid switch). We conclude that hydromorphone is a flexible second-line alternative to morphine that is particularly useful when intolerable side-effects are experienced with other opioids. In renal impairment (including two patients with end-stage renal failure) we found hydromorphone to be safe and effective. Further clinical and pharmacokinetic studies are required.

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

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

Selective effects of somatostatin analogs on human drug-metabolizing enzymes

Pharmacologic or surgical manipulation with growth hormone secretion or with the physiologic release of somatostatin and growth hormone-releasing hormone affects some rat liver enzymes, especially the sex-differentiated ones. We investigated the effects of two somatostatin analogs on several enzyme functions in six patients with carcinoid syndrome, using codeine as a probe drug. Codeine was given intravenously and its N- and O-demethylation, as well as 6-glucuronidation catalyzed by CYP3A, CYP2D6, and uridine diphosphate-glucuronosyltransferase, respectively, were studied before and during treatment with somatostatins. After 3 days of treatment with somatostatins the partial metabolic clearance of codeine by N-demethylation decreased by 21% to 64% in all patients (mean change, 44%; p < 0.05), and the clearance by O-demethylation was decreased by 20% to 69% in five of the patients (mean change in all patients, 35%; p < 0.05). In contrast, the partial clearance by 6-glucuronidation and the total systemic clearance of codeine were unchanged. Our results may be caused by the inhibition of growth hormone secretion induced by the somatostatins, inasmuch as direct metabolic interactions with these peptide drugs are improbable. The decline in CYP3A4 and CYP2D6 activity might have clinical implications when substrates of these enzymes with low therapeutic indices are combined with somatostatin analogs. Because the formation of morphine from codeine was altered, the analgesic effect of this drug may be reduced during concomitant treatment with somatostatins.