Meperidine-induced delirium

Delirium and its Pharmacological Causes in Older People, Part Two

Delirium is a syndrome that can arise from many causes or underlying conditions, and though it has been reported in younger patients, it is more prevalent in older people, though it can occur in other age groups as well. Identifying delirium is challenging in older people because of the coexistence of underlying dementia or depression, which may further complicate the presentation. Drug-induced delirium is one of the major causes of delirium, and evaluation of this potential cause or contribution is an important component of the evaluation process, since it can lead to poor patient outcomes. Part one of this three part series reviewed the epidemiology, pathophysiology, evaluation, diagnostic process, and causes of delirium in older people, with a focus on the pharmacological causes. Part two of this series continues to review drugs and drug classes that can cause or contribute to delirium in older people.

Analgesia in acute ischemic chest pain

Analgesics, particularly opioids, have been routinely used in the emergency treatment of ischemic chest pain for a long time. In the past two decades; however, several studies have raised the possibility of the harmful effects of opioid administration. In 2014, the American Heart Association (AHA)/American College of Cardiology Foundation (ACCF) changed the guidelines regarding the use of opioids from class IC to class IIb for non-ST elevation acute coronary syndrome. And in 2015, the European Society of Cardiology (ESC) guidelines incidentally noted the side effects of opioids. In ST-segment elevation myocardial infarction, both ESC and AHA/ACCF still recommend the use of opioids. Given the need for adequate pain relief in ischemic chest pain in the emergency setting, it is necessary to understand the adverse effects of analgesia, while still providing sufficiently potent options for analgesia. The primary purpose of this review is to quantify the effects of analgesics commonly used in the prehospital and emergency department in patients with ischemic chest pain.

Impact of cytochrome P450 variation on meperidine N-demethylation to the neurotoxic metabolite normeperidine

1. Meperidine is an opioid analgesic that undergoes N-demethylation to form the neurotoxic metabolite normeperidine. Previous studies indicate that meperidine N-demethylation is catalyzed by cytochrome P450 2B6 (CYP2B6), CYP3A4, and CYP2C19.2. The purpose of this study was to examine the relative P450 contributions to meperidine N-demethylation and to evaluate the effect of CYP2C19 polymorphism on normeperidine generation. Experiments were performed using recombinant P450 enzymes, selective chemical inhibitors, enzyme kinetic assays, and correlation analysis with individual CYP2C19-genotyped human liver microsomes.3. The catalytic efficiency (k_cat/K_m) for meperidine N-demethylation was similar between recombinant CYP2B6 and CYP2C19, but markedly lower by CYP3A4.4. In CYP2C19-genotyped human liver microsomes, normeperidine formation was significantly correlated with CYP2C19 activity (S-mephenytoin 4´-hydroxylation).5. CYP2C19 inhibitor (+)-N-3-benzylnirvanol and CYP3A inhibitor ketoconazole significantly reduced microsomal normeperidine generation by an individual donor with high CYP2C19 activity, whereas donors with lower CYP2C19 activity were sensitive to inhibition by ketoconazole but not benzylnirvanol.6. These findings demonstrate that the relative CYP3A4, CYP2B6, and CYP2C19 involvement in meperidine N-demethylation depends on the enzyme activities in individual human liver microsomal samples. CYP2C19 is likely an important contributor to normeperidine generation in individuals with high CYP2C19 activity, but additional factors influence inter-individual metabolite accumulation.

The Comparative Risk of Delirium with Different Opioids: A Systematic Review

Objective

There is substantial evidence that the use of opioids increases the risk of adverse outcomes such as delirium, but whether this risk differs between the various opioids remains controversial. In this systematic review, we evaluate and discuss possible differences in the risk of delirium from the use of various types of opioids in older patients.

Methods

We performed a search in MEDLINE by combining search terms on delirium and opioids. A specific search filter for use in geriatric medicine was used. Quality was scored according to the quality assessment for cohort studies of the Dutch Cochrane Institute.

Results

Six studies were included, all performed in surgical departments and all observational. No study was rated high quality, one was rated moderate quality, and five were rated low quality. Information about dose, route, and timing of administration of the opioid was frequently missing. Pain and other important risk factors of delirium were often not taken into account. Use of tramadol or meperidine was associated with an increased risk of delirium, whereas the use of morphine, fentanyl, oxycodone, and codeine were not, when compared with no opioid. Meperidine was also associated with an increased risk of delirium compared with other opioids, whereas tramadol was not. The risk of delirium appeared to be lower with hydromorphone or fentanyl, compared with other opioids. Numbers used for comparisons were small.

Conclusion

Some data suggest that meperidine may lead to a higher perioperative risk for delirium; however, high-quality studies that compare different opioids are lacking. Further comparative research is needed.

Electronic supplementary material

The online version of this article (doi:10.1007/s40266-017-0455-9) contains supplementary material, which is available to authorized users.

Opioid-induced Hallucinations: A Review of the Literature, Pathophysiology, Diagnosis, and Treatment

Despite their association with multiple adverse effects, opioid prescription continues to increase. Opioid-induced hallucination is an uncommon yet significant adverse effect of opioid treatment. The practitioner may encounter patient reluctance to volunteer the occurrence of this phenomenon because of fears of being judged mentally unsound. The majority of the literature concerning opioid-induced hallucinations arises from treatment during end-of-life care and cancer pain. Because the rate of opioid prescriptions continues to increase in the population, the rate of opioid-associated hallucinations may also conceivably increase. With a forecasted increase in the patient-to-physician ratio, opioid therapy is predicted to be provided by practitioners of varying backgrounds and medical specialties. Hence, knowledge of the pharmacology and potential adverse effects of these agents is required. This review seeks to increase awareness of this potential complication through a discussion of the literature, potential mechanisms of action, diagnosis, and treatment strategies.

The safety of meperidine prescribing in older adults: A longitudinal population-based study

BACKGROUND

Meperidine (pethidine) is an opioid analgesic that offers little advantage relative to other opioids and several disadvantages including limited potency, short duration of action, and the production of a neurotoxic metabolite (normeperidine) with a long half-life. Older adults are more sensitive to meperidine's side effects and may have diminished renal function which leads to the accumulation of normeperidine. The Institute for Safe Medication Practices has suggested avoiding meperidine in older adults, limiting its dose (≤600 mg/day) and duration of use (≤48 h). The objective of this study was to determine the level of meperidine use in older adults and assess the dosage and duration of meperidine with reference to these safety recommendations.

METHODS

A longitudinal study using administrative healthcare data was conducted to examine meperidine utilization and levels of high dose and extended duration prescribing among persons ≥65 years of age between April 1, 2001, and March 31, 2014 in Manitoba, Canada. The number of meperidine prescriptions, users, duration of treatment, defined daily doses (DDD) dispensed and number of prescribers were determined over the study period.

RESULTS

In the Manitoba older adult population there was a marked decline in meperidine users and prescriptions from 2001 to 2014. There was an average use of 26.4 (95 % CI 24.0-28.8) DDDs of meperidine per user per year. While only 3.7 % of the prescriptions exceeded the 600 mg maximum daily dose, 96.7 % of prescriptions exceeded the recommended 2 days of therapy. For the remaining users of meperidine, the amount of meperidine used per person rose from 18.98 to 56.14 DDDs/user/year over the study period. The number of prescribers of meperidine declined throughout the study, but low DDD prescribers declined more quickly than high DDD prescribers.

CONCLUSIONS

While meperidine use has declined, the remaining use appears to be decreasing in safety, with more meperidine prescribed per user. This seems to be driven by the continued prescribing by a small number of high DDD prescribers. Targeted educational initiatives directed at this small group of prescribers may be helpful. Alternatively removing meperidine from medication insurance schemes may provide additional incentive to avoid meperidine in older adults.

Voluntary warnings and the limits of good prescribing behavior: the case for de-adoption of meperidine

Background

Meperidine (pethidine) offers little to no therapeutic advantage over other opioids, may be more prone to abuse, and produces a neurotoxic metabolite with a long half-life. The Institute for Safe Medication Practices (ISMP) issued warnings in 2004 and 2005 suggesting that meperidine be avoided, and when used, it should be in limited doses (<600 mg/24 h) and for a limited duration (<48 hours). Hospitals have responded to these warnings, but much less is known about meperidine prescribing in the community setting. This study examined the potential impact of ISMP warnings on the prescribing of meperidine using time series analysis.

Methods

A population-based longitudinal cross-sectional study was conducted to examine oral meperidine utilization among persons 16 years of age and older in Manitoba, Canada, between April 1, 2001 and March 31, 2014. Amounts of meperidine were expressed using defined daily doses (DDDs), the equivalent of 400 mg of meperidine per day. The number of meperidine prescriptions and users per quarter were determined and analyzed using regression analysis.

Results

There were 49,063 prescriptions for 442,641 DDDs of meperidine dispensed to 9,374 distinct users. The number of DDDs of meperidine per 1,000 persons peaked in the second quarter of 2003 at 11.75, and then dropped to a low of 5.36 by 2014. This represented a marked decline in the numbers of users and prescriptions over the study period. The piecewise regression model revealed a significant breakpoint in the last quarter of 2004 (F_{(3, 48)}=337.00, P<0.0001). In contrast to these findings, among the remaining users, there was an increase in the amount of meperidine per prescription (increase of 0.34 DDDs/prescription/year; F(1, 50)=434, P<0.0001, R²=0.89) and the amount of meperidine per user (increase of 1.17 DDDs/user/year; F(1, 50)=653.5, P<0.0001, R²=0.93).

Conclusion

Following the ISMP warnings, meperidine use dramatically declined. Unfortunately, the remaining users of meperidine are using more meperidine and receiving more meperidine in each prescription. This pattern of results suggests that there may be limits to voluntary safety warnings. Policy action such as removal of medication insurance coverage may represent a logical next step to reverse or de-adopt meperidine and further enhance patient safety.

Common biological pathways underlying the psychoneurological symptom cluster in cancer patients

BACKGROUND

A symptom cluster is a group of symptoms that occur together and are interrelated. The clinical implication of symptom cluster research is to use the clustering patterns of symptoms to understand the mechanisms for these symptoms and develop management strategies targeted at multiple symptoms.

OBJECTIVE

The purposes of this review were to summarize the evidence for a psychoneurological symptom cluster in cancer patients, to provide information regarding the underlying biological mechanisms for each of the psychoneurological symptoms within the cluster, and to propose possible common biological pathways that may underlie this cluster.

METHODS

A systematic review of the literature was conducted.

RESULTS

Empirical evidence exists to support a cluster of psychoneurological symptoms (ie, depressive symptoms, cognitive disturbance, fatigue, sleep disturbance, pain). At a molecular level, common biological pathways (ie, proinflammatory cytokines, hypothalamic-pituitary-adrenal axis, and monoamine neurotransmission system) may underlie the development of symptoms within this cluster. Activation of proinflammatory cytokines is proposed as a first stage of mechanistic pathway. However, other biological factors, such as lowered estrogen or hemoglobin levels, may influence psychoneurological cluster.

CONCLUSION

Additional studies are needed to confirm the roles of cytokines as well as other biological factors in the development of the psychoneurological cluster and to determine the biomarkers to identify the subgroups of cancer patients who are at greatest risk for this cluster.

IMPLICATIONS FOR PRACTICE

This information can be used by researchers and clinicians to guide the selection of symptom management strategies that are ideally targeted to the biological mechanisms that underlie this symptom cluster.

Treatment of four psychiatric emergencies in the intensive care unit

OBJECTIVES

To review the diagnosis and management of four selected psychiatric emergencies in the intensive care unit: agitated delirium, neuroleptic malignant syndrome, serotonin syndrome, and psychiatric medication overdose.

DATA SOURCES

Review of relevant medical literature.

DATA SYNTHESIS

Standardized screening for delirium should be routine. Agitated delirium should be managed with an antipsychotic and, possibly, dexmedetomidine in treatment-refractory cases. Delirium management should also include ensuring a calming environment and adequate pain control, minimizing benzodiazepines and anticholinergics, normalizing the sleep-wake cycle, providing sensory aids as required, and providing early physical and occupational therapy. Neuroleptic malignant syndrome should be treated by discontinuing dopamine blockers, providing supportive therapy, and possibly administering medications (benzodiazepines, dopamine agonists, and/or dantrolene) or electroconvulsive therapy, if indicated. Serotonin syndrome should be treated by discontinuing all serotonergic agents, providing supportive therapy, controlling agitation with benzodiazepines, and possibly administering serotonin2A antagonists. It is often unnecessary to restart psychiatric medications upon which a patient has overdosed in the intensive care unit, though withdrawal syndromes should be prevented, and communication with outpatient prescribers is vital.

CONCLUSIONS

Understanding the diagnosis and appropriate management of these four psychiatric emergencies is important to provide safe and effective care in the intensive care unit.

Postoperative complications: delirium

Delirium is a common feature of the postoperative period, leading to increased morbidity and mortality and significant costs. Multiple factors predispose a patient to delirium in its hypoactive, hyperactive, or mixed forms. Tools have been validated for its quick and accurate identification to ensure timely and effective multidisciplinary intervention and treatment. A significant percentage of patients may require placement in skilled nursing facilities or similar care environments because of the long-lasting effects. The physician must be vigilant in the search for and identification of all forms of delirium and must effectively treat the underlying medical condition and symptoms.

Delirium in Palliative Care Patients: Focus on Pharmacotherapy

Patients receiving palliative care often possess multiple risk factors and predisposing conditions for delirium. The impact of delirium on patient care in this population may also be far-reaching: affecting not only quality of remaining life but the dying process experienced by patients, caregivers, and the medical team as well. As palliative care focuses on comfort and symptom management, the approach to assessment and subsequent treatment of delirium in palliative care patients may prove difficult for providers to navigate. This article summarizes the multifactorial nature, numerous predisposing medical risk factors, neuropsychiatric adverse effects of palliative medications, pharmacokinetic changes, and challenges complicating delirium assessment and provides a systematic framework for assessment. The benefits, risks, and patient-specific considerations for treatment selection are also discussed.

Radiation, chemotherapy, and symptom management in cancer-related cognitive dysfunction

Patients with cancer are concerned about their ability to interact with friends and family and to perform activities associated with daily living. The combined effects of the disease process, its treatment with surgery, radiation, and chemotherapy, and the medications used to manage symptoms may all impact cognitive function. Minimizing the effect of each treatment modality on cognitive processing requires an understanding of how these treatment modalities may impact cognition.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

Side-effects of opioids in chronic pain treatment

The emergence of opioid-induced neurotoxicity has gained increasing recognition in the literature in the past decade. Exciting developments at the receptor and intracellular level have revealed some insights into the potential mechanisms underlying this phenomenon. The hitherto reported clinical benefits of opioid rotation and dose reduction in the treatment of opioid toxicity warrant further clarification in prospective studies, particularly in relation to their relative value.

Catatonia Associated with Coadministration of Tramadol and Meperidine

Tramadol and meperidine are frequently prescribed medications in the management of oncologic patients. The pharmacologic interaction of these two drugs may induce mental disturbance. This was demonstrated by our case of a 39-year-old woman with gastric mucosa associated lymphoid tissue lymphoma (MALToma), stage III after chemotherapy. She was admitted to our medical ward with the complaint of abdominal pain. Pantoprazole 40 mg and tramadol 150 mg daily were prescribed with intravenous route after hospitalization. Two days later, the patient developed transient visual hallucinations and disorientation after additional injection of meperidine (25 mg). Six hours later, catatonic features appeared. The duty doctor stopped all the medications. Two days later, the catatonic features disappeared. From the clinical course, we suggest that the catatonia was caused by drug interactions between tramadol and meperidine. The pharmacodynamic mechanism might be related to the dopamine and serotonin systems.

Nitrous oxide does not change the incidence of postoperative delirium or cognitive decline in elderly surgical patients

BACKGROUND

Postoperative delirium and cognitive decline are common in elderly surgical patients after non-cardiac surgery. Despite this prevalence and clinical importance, no specific aetiological factor has been identified for postoperative delirium and cognitive decline. In experimental setting in a rat model, nitrous oxide (N(2)O) produces neurotoxic effect at high concentrations and in an age-dependent manner. Whether this neurotoxic response may be observed clinically has not been previously determined. We hypothesized that in the elderly patients undergoing non-cardiac surgery, exposure to N(2)O resulted in an increased incidence of postoperative delirium than would be expected for patients not receiving N(2)O.

METHODS

Patients who were >or=65 yr of age, undergoing non-cardiac surgery and requiring general anaesthesia were randomized to receive an inhalational agent and either N(2)O with oxygen or oxygen alone. A structured interview was conducted before operation and for the first two postoperative days to determine the presence of delirium using the Confusion Assessment Method.

RESULTS

A total of 228 patients were studied with a mean (range) age of 73.9 (65-95) yr. After operation, 43.8% of patients developed delirium. By multivariate logistic regression, age [odds ratio (OR) 1.07; 95% confidence interval (CI) 1.02-1.26], dependence on performing one or more independent activities of daily living (OR 1.54; 95% CI 1.01-2.35), use of patient-controlled analgesia for postoperative pain control (OR 3.75; 95% CI 1.27-11.01) and postoperative use of benzodiazepine (OR 2.29; 95% CI 1.21-4.36) were independently associated with an increased risk for postoperative delirium. In contrast, the use of N(2)O had no association with postoperative delirium.

CONCLUSIONS

Exposure to N(2)O resulted in an equal incidence of postoperative delirium when compared with no exposure to N(2)O.

The role of postoperative analgesia in delirium and cognitive decline in elderly patients: a systematic review

Postoperative delirium and cognitive decline are adverse events that occur frequently in elderly patients. Preexisting patient factors, medications, and various intraoperative and postoperative causes have been implicated in the development of postoperative delirium and cognitive decline. Despite previous studies identifying postoperative pain as a risk factor, relatively few clinical studies have compared the effect of common postoperative pain management techniques (IV and epidural) or opioid analgesics on postoperative cognitive status. A systematic search of the PubMed and CINAHL databases identified six studies comparing different opioid analgesics on postoperative delirium and cognitive decline and five studies comparing IV and epidural routes of administering analgesia. Meperidine was consistently associated with an increased risk of delirium in elderly surgical patients, but the current evidence has not shown a significant difference in postoperative delirium or cognitive decline among other more frequently used postoperative opioids such as morphine, fentanyl, or hydromorphone. The available studies also suggest that IV or epidural techniques do not influence cognitive function differently. However, future investigations of sufficient study size and more standardized methods of defining outcomes are necessary to confirm the current findings.

Psychotogenic drugs and delirium pathogenesis: the central role of the thalamus

Delirium is thought to be a temporary psychiatric disorder resulting from a reduced central cholinergic transmission, combined with an increased dopaminergic transmission. The cholinergic and the dopaminergic systems interact not only with each other but with glutamatergic and gamma-amino-butyric acid (GABA) pathways. Besides the cerebral cortex, critical anatomical substrates of psychosis pathophysiology would comprise the striatum, the substantia nigra/ventral tegmental area, and the thalamus. The thalamus acts as a filter, allowing only the relevant information to travel to the cortex. Drugs of abuse (e.g. PCP, Ecstasy), as well as psychoactive medications frequently prescribed to hospitalized patients (e.g. benzodiazepines, opioids) could compromise the thalamic gating function, leading to sensory overload and hyperarousal. We propose that drug-induced delirium would result from the transient thalamic dysfunction caused by exposure to medications that interfere with central glutamatergic, GABAergic, dopaminergic and cholinergic pathways at critical sites of action. This model provides directions for future studies in neurophysiology, in vivo brain imaging, and psychopharmacology investigating delirium neuropathophysiology.

Determinants of prescribing meperidine compared to morphine in hospitalized patients

Morphine is a preferred narcotic since meperidine forms toxic metabolites. Determinants of meperidine use have been poorly described. The objective of this study is to explore factors associated with the ordering of meperidine versus morphine. Retrospective chart review of adult patients, randomly selected based on orders for morphine or meperidine. 1552 orders were written for 670 patients. Of these, 36% were for meperidine. In multivariable analysis, the ordering of meperidine was associated with the following variables in decreasing order of importance: physician specialty, total doses received, hospital location, patient race, age and insurance, and physician gender. More orders for meperidine were written for those receiving fewer doses. Though meperidine has little role in the routine management of hospital pain, we found it continues to be used frequently. Importantly, meperidine is ordered more frequently for patients who receive shorter courses of narcotics. Our study suggests that interventions targeted at more appropriate use of meperidine rather than complete elimination might be more acceptable to physicians while minimizing the risk of toxicity.

Anticholinergic Syndrome After Anesthesia: A Case Report and Review

Anticholinergic syndrome may present with a wide variety of signs and symptoms. Central manifestations range from excitatory symptoms including delirium and agitation to central nervous system depression, stupor and coma. Anticholinergic syndrome was once a common phenomenon after general anesthesia because of the frequent administration of the anticholinergic agents atropine and scopolamine. Now that these agents are rarely administered, anesthesia-related anticholinergic syndrome is currently infrequently reported. Still, many prescription and over the counter medications as well as many anesthetic agents possess anticholinergic activity, and this diagnosis should be considered in patients with altered mental status following general anesthesia. We report a case of prolonged somnolence following general anesthesia for an MRI. A rapid improvement of mental status with physostigmine confirmed the diagnosis of anticholinergic syndrome. This case is unique in that anticholinergic syndrome-related respiratory depression was promptly reversed with physostigmine.

The panorama of opioid-related cognitive dysfunction in patients with cancer: a critical literature appraisal

BACKGROUND

Opioids have an essential role in the management of pain in cancer patients, particularly those with advanced disease. Cognitive dysfunction is a recognized complication of opioid use. However, misconceptions and controversy surround the nature and prevalence of its occurrence. A projected increase in the aging cancer population highlights the need for a better understanding of this phenomenon.

METHODS

A critical appraisal of the literature evidence in relation to the pattern, pathophysiology, assessment, impact, and management of cognitive dysfunction due to opioid use in cancer pain management is given.

RESULTS

Studies in cancer patients with less advanced disease reveal subtle evidence of cognitive impairment, largely related to initial dosing or dose increases. In advanced cancer, opioid-induced cognitive dysfunction usually occurs in the form of delirium, a multifactorial syndrome. The presence of both cognitive impairment and delirium frequently is misdiagnosed or missed. Potential risk factors include neuropathic and incidental pain, opioid tolerance, somatization of psychologic distress, and a history of drug or alcohol abuse. Elevation of opioid metabolites with renal impairment may contribute to cognitive dysfunction. Recognition of opioid-related cognitive dysfunction is improved by objective screening. Successful management requires either dose reduction or a change of opioid, in addition to addressing other reversible precipitants such as dehydration or volume depletion.

CONCLUSIONS

Opioid-related cognitive dysfunction tends to be subtle in the earlier stages of cancer, whereas delirium, a more florid form with behavioral disturbance is likely to be present in the advanced cancer population. In patients with advanced disease, an optimal management approach requires careful clinical assessment, identification of risk factors, objective monitoring of cognition, maintenance of adequate hydration, and either dose reduction or switching to a different opioid.

Strategies for the treatment of cancer pain in the new millennium

As was the case in the era before us, in the new millennium we will continue to see an abundance of patients experiencing cancer-related pain for different reasons. Although much needless pain and suffering still affects many of those with cancer, we are presented with a medical dichotomy. With the analgesic drugs available today, and the relatively simple and effective guidelines to treat cancer pain published and disseminated by the World Health Organization, why do people with cancer continue to experience pain? As we search for the answer, the horizon may hold promising new drugs, 'old drugs' with new interest and applications, and new strategies for the field of pain therapy. Possibilities include the isolation and development of analgesics or analgesic combinations that may minimise the adverse effects which are often associated with the current therapeutic class of opioid analgesics. In addition, current research points to promising results identifying the N-methyl D-aspartate non-opioid receptor as a likely component of neuropathic pain. Drugs such as gabapentin, the mechanism of action of which is not well known, have found favour within the clinical community for their analgesic properties and good tolerability. Methadone, in a phase of resurgence, has garnered the attention of the clinical community because of its unique receptor activity and pharmacoeconomic benefits. A number of clinical studies have demonstrated that methadone has a valuable role in treating cancer pain. Perhaps, an unbalanced focus on the risks of inappropriate use, rather than the benefits, should not compromise or distract from the use of methadone as an alternative to morphine. Studies are on going to assess the potential role of methadone in treating neuropathic pain. Drugs such as cannabinoids, although currently applicable for patients with anorexia, nausea and/or vomiting, may offer benefits to patients experiencing pain. Other opportunities exist with such compounds as alpha2-adrenergic agonists, nicotine, lidocaine and ketamine. New strategies such as the switching opioids and/or their route of administration may offer improved analgesia with fewer adverse effects, thus providing therapeutic alternatives for the clinical community. In addition, there is interest in the co-administration of opioids that act on different receptors. For instance, oxycodone appears to be a kappa opioid receptor agonist and may offer enhanced analgesia when combined with morphine.

Meperidine: a critical review

Meperidine was initially synthesized as an anticholinergic agent but was soon discovered to have analgesic properties. Although meperidine's anticholinergic effects were demonstrated in vivo, the anticholinergic effects on the biliary and renal tracts have not been demonstrated in vivo. Studies have clearly demonstrated that meperidine is no more efficacious in treating biliary or renal tract spasm than comparative mu opioids. The initial studies demonstrating the analgesic efficacy of meperidine were mostly case reports and not double-blind, randomized, controlled trials in specific populations. Subsequent comparative studies failed to demonstrate any advantages of meperidine over comparable doses of other analgesics. Meperidine was portrayed in practice and teaching as having unique clinical advantages. The analgesic effects of meperidine are not pronounced, and, in addition, meperidine use is complicated by unique side effects including serotonergic crisis and normeperidine toxicity. Meperidine's poor efficacy, toxicity, and multiple drug interactions have resulted in a movement to replace meperidine with more efficacious and less toxic opioid analgesics.

Cognitive toxicity of drugs used in the elderly

The aged are an extremely heterogeneous population that is growing worldwide, included are healthy and agile individuals in their early sixties, as well as an increasing number of people over the age of 35. Pharmacotherapy is expected to continue its prominent role in the medical management of a wide range of conditions that affect older people. Adverse consequences of all kinds complicate the use of medications, and such events seem to increase in incidence with polypharmacy. Cognitive impairment can occur during the course of treatment with a wide range of medications and can have a variety of presentations, Both the number of concurrent medications that older individuals routinely use and physiologic changes in these patients render them more susceptible to developing cognitive toxicity. Most of the frequently implicated medications carry documentation of their ability to cause cognitive disturbances in their package labeling, suggesting that the level of vigilance for adverse effects during the course of their use should always be high. Such caution can be used to guide appropriate drug treatment of the aged so that clinicians do not need to opt for undertreatment to avoid toxicity.

Update on pain management for advanced genitourinary cancer

PURPOSE

Pain is a significant problem in many patients with genitourinary malignancy at all stages of disease. Optimal pain control becomes a primary concern as disease progresses and other therapies are exhausted. The selection of the most appropriate therapy becomes difficult without an understanding of the underlying mechanisms of pain and the available therapies.

MATERIALS AND METHODS

A review of the literature regarding the mechanisms and assessment of pain syndromes was performed. All available therapies were investigated with respect to conservative management with opioid medications and adjuvant drugs, and the indications for invasive techniques.

RESULTS

Increased understanding of the mechanisms and classification of pain syndromes has led to improved assessment and treatment. Despite these advances a significant number of patients have inadequate pain control and the education of treating physicians remains an important target for improving this situation.

CONCLUSIONS

Opioid medication is the mainstay of therapy in the majority of patients but with the appropriate addition of other adjuvant drugs patients may achieve optimal pain control without unwanted side effects. A few patients benefit from more invasive techniques, including plexus blocks and neuraxial infusion therapy, and the indications for these treatments are discussed. These therapies have largely superseded neuroablative procedures that are more destructive and associated with higher morbidity.

Strategies to manage the adverse effects of oral morphine: an evidence-based report

Successful pain management with opioids requires that adequate analgesia be achieved without excessive adverse effects. By these criteria, a substantial minority of patients treated with oral morphine (10% to 30%) do not have a successful outcome because of (1) excessive adverse effects, (2) inadequate analgesia, or (3) a combination of both excessive adverse effects along with inadequate analgesia. The management of excessive adverse effects remains a major clinical challenge. Multiple approaches have been described to address this problem. The clinical challenge of selecting the best option is enhanced by the lack of definitive, evidence-based comparative data. Indeed, this aspect of opioid therapeutics has become a focus of substantial controversy. This study presents evidence-based recommendations for clinical-practice formulated by an Expert Working Group of the European Association of Palliative Care (EAPC) Research NETWORK: These recommendations highlight the need for careful evaluation to distinguish between morphine adverse effects from comorbidity, dehydration, or drug interactions, and initial consideration of dose reduction (possibly by the addition of a co analgesic). If side effects persist, the clinician should consider options of symptomatic management of the adverse effect, opioid rotation, or switching route of systemic administration. The approaches are described and guidelines are provided to aid in selecting between therapeutic options.

Delirium in the intensive care unit: are we helping the patient?

The intensive care unit (ICU) represents a dynamic interaction between patient factors and interventional factors. The complexity of this situation can generate an impaired consciousness in the patients. The critical care provider is faced with deducing the etiology and treatment of delirium in the ICU. Many of the therapeutic agents that are used in the ICU may precipitate delirium. Patients may also experience delirium as part of their underlying medical conditions. Withdrawal syndromes, delirium tremens in particular, are known to cause delirium. By a combination of appropriate selection of medications and an awareness of delirium as a side effect, the patient in the ICU may be treated in a manner to minimize the clouding of consciousness. An understanding of the proposed pathophysiology of various types of delirium will allow appropriate clinical measures to be taken.

Successful treatment of normeperidine neurotoxicity by hemodialysis

Normeperidine, a major metabolite of meperidine, is half as potent as meperidine as an analgesic but two to three times more potent as a convulsant. Renal failure significantly increases the plasma half-life of normeperidine. The intensity of the central nervous system excitation is highly correlated with the plasma concentration of normeperidine. Moreover, normeperidine toxicity is not reversed by naloxone, which may exacerbate it. We report a patient with end-stage renal disease undergoing maintenance continuous cycler peritoneal dialysis who had been receiving meperidine for pain control. The patient subsequently developed myoclonic contractions and a grand mal seizure. The patient was successfully treated with hemodialysis (using an F8 dialyzer) for presumed normeperidine-induced seizure. During hemodialysis, normeperidine average blood clearance was 73 mL/min, average plasma clearance was 50 mL/min, and average percentage of plasma extraction was 24%. There also was a 26% reduction in plasma concentration of normeperidine over 3 hours of hemodialysis. In conclusion, our findings suggest that hemodialysis may be used effectively for treating patients with suspected normeperidine-induced neurotoxicity.

Metabolism of drugs of abuse by cytochromes P450

Studies of most drugs of abuse utilize in vivo animal experimentation so that the responses measured reflect the pharmacokinetics of the administered drug as well as its pharmacodynamics. These drugs are generally lipid soluble chemicals and their elimination is dependent on metabolism, so an understanding of this process is critical to the interpretation of responses. This review summarizes the interaction between drugs of abuse and cytochromes P450, the oxidative enzymes that catalyze the first step of the metabolic process. Although they process their substrates by a common chemical mechanism, these enzymes differ markedly in their regulation, i.e. induction and inhibition, their substrate selectivities, the metabolites they generate and their relative concentration in different species. The activity of an enzyme catalyzing a specific metabolic reaction can be altered by prior xenobiotic exposure, by its genetics and by a co-administered drug, so that the pharmacokinetics of the drug under study can vary with the history of the individual subject. These issues are obviously important in human studies so, when possible, the relevant human enzymes involved in the processes described have been identified.

Delirium in the elderly. Optimal management

Delirium is common, morbid and costly, especially among hospitalised elderly patients. Nonetheless, it remains under-recognised and often poorly managed. This article summarises the 5 key steps in the optimal management of delirium. The first step is to precisely define the syndrome of delirium, using key features described in the Diagnostic and Statistical Manual of Mental Disorders (fourth edition) [DSM-IV] or the Confusion Assessment Method. Key features include an acute onset of mental status change, fluctuating course, the presence of inattention, and either disorganised thinking or an altered level of of consciousness. The second step involves the identification of patients at high risk of delirium before it develops, so that preventive measures can be implemented. Risk factors for delirium include advanced age, dementia, impaired functional status, chronic comorbidities and medications, and the severity of the acute illness or surgery. The third step is improved recognition of delirium. Very often, the presence of delirium is neither diagnosed nor properly documented in the medical record. The fourth step is to appropriately evaluate the delirious patient to assess all important contributors to the syndrome. This evaluation will usually involve a careful history, medication review, physical examination and selected laboratory testing. The fifth, and most important, step is the management of the delirious patient. The key elements of management are treating the primary condition(s) leading to delirium, removing all treatable contributing factors, maintaining behavioural control, and supporting the patient and their family.

Pethidine-associated seizure in a healthy adolescent receiving pethidine for postoperative pain control

A healthy 17-year-old male received standard intermittent doses of pethidine via a patient-controlled analgesia (PCA) pump for management of postoperative pain control. Twenty-three h postoperatively he developed a brief self-limited seizure. Both plasma pethidine and norpethidine were elevated in the range associated with clinical manifestations of central nervous system excitation. No other risk factors for CNS toxicity were identified. This method allowed frequent self-dosing of pethidine at short time intervals and rapid accumulation of pethidine and norpethidine. The routine use of pethidine via PCA even for a brief postoperative analgesia should be reconsidered.