Comparison of paracetamol metabolism in young adult and elderly males

Why paracetamol (acetaminophen) is a suitable first choice for treating mild to moderate acute pain in adults with liver, kidney or cardiovascular disease, gastrointestinal disorders, asthma, or who are older

Acute pain is among the most common reasons that people consult primary care physicians, who must weigh benefits versus risks of analgesics use for each patient. Paracetamol (acetaminophen) is a first-choice analgesic for many adults with mild to moderate acute pain, is generally well tolerated at recommended doses (≤4 g/day) in healthy adults and may be preferable to non-steroidal anti-inflammatory drugs that are associated with undesirable gastrointestinal, renal, and cardiovascular effects. Although paracetamol is widely used, many patients and physicians still have questions about its suitability and dosing, especially for older people or adults with underlying comorbidities, for whom there are limited clinical data or evidence-based guidelines. Inappropriate use may increase the risks of both overdosing and inadequate analgesia. To address knowledge deficits and augment existing guidance in salient areas of uncertainty, we have researched, reviewed, and collated published evidence and expert opinion relevant to the acute use of paracetamol by adults with liver, kidney, or cardiovascular diseases, gastrointestinal disorders, asthma, or/and who are older. A concern is hepatotoxicity, but this is rare among adults who use paracetamol as directed, including people with cirrhotic liver disease. Putative epidemiologic associations of paracetamol use with kidney or cardiovascular disease, hypertension, gastrointestinal disorders, and asthma largely reflect confounding biases and are of doubtful relevance to short-term use (<14 days). Paracetamol is a suitable first-line analgesic for mild to moderate acute pain in many adults with liver, kidney or cardiovascular disease, gastrointestinal disorders, asthma, and/or who are older. No evidence supports routine dose reduction for older people. Rather, dosing for adults who are older and/or have decompensated cirrhosis, advanced kidney failure, or analgesic-induced asthma that is known to be cross-sensitive to paracetamol, should be individualized in consultation with their physician, who may recommend a lower effective dose appropriate to the circumstances.

Highly Variable Paracetamol Pharmacokinetics After Multiple Oral Dosing in Frail Older People: A Population Pharmacokinetic Analysis

INTRODUCTION

Paracetamol pharmacokinetics (PK) is highly variable in older fit adults after intravenous administration. Frailty and oral administration likely result in additional variability. The aim was to determine oral paracetamol PK and variability in geriatric inpatients.

METHODS

A population PK analysis, using NONMEM 7.2, was performed on 245 paracetamol samples in 40 geriatric inpatients (median age 87 [range 80-95] years, bodyweight 66.4 [49.3-110] kg, 92.5% frail [Edmonton Frail Scale]). All subjects received paracetamol 1000 mg as tablet (72.5%) or granulate (27.5%) three times daily. Simulations of dosing regimens (1000 mg every 6 hours [q6h] or q8h) were performed to determine target attainment, using mean steady-state concentration (C_ss-mean) of 10 mg/L as target.

RESULTS

A one-compartment model with first order absorption and lag time best described the data. The inter-individual variability was high, with absorption rate constant containing the highest variability. The inter-individual variability could not be explained by covariates. Simulations of 1000 mg q6h and q8h resulted in a C_ss-mean of 10.8 [25-75th percentiles 8.2-12.7] and 8.13 [6.3-9.6] mg/L, respectively, for the average geriatric inpatient. The majority of the population remained off-target (22.2% [q6h] and 52.2% [q8h] <8 mg/L; 31.3 [q6h] and 7.6% [q8h] >12 mg/L).

CONCLUSION

A population of average geriatric inpatients achieved target C_ss-mean with paracetamol 1000 mg q6h, while q8h resulted in underexposure for the majority of them. Due to high unexplained variability, a relevant proportion remained either above or below the target concentration of 10 mg/L. Research focusing on PK, efficacy and safety is needed to recommend dosing regimens.

Short-Term Safety of Repeated Acetaminophen Use in Patients With Compensated Cirrhosis

Current guidelines recommend restricting acetaminophen (APAP) use in patients with cirrhosis, but evidence to support that recommendation is lacking. Prior studies focused on pharmacokinetics (PK) of APAP in cirrhosis but did not rigorously examine clinical outcomes, sensitive biomarkers of liver damage, or serum APAP‐protein adducts, which are a specific marker of toxic bioactivation. Hence, the goal of this pilot study was to test the effects of regularly scheduled APAP dosing in a well‐defined compensated cirrhosis group compared to control subjects without cirrhosis, using the abovementioned outcomes. After a 2‐week washout, 12 subjects with and 12 subjects without cirrhosis received 650 mg APAP twice per day (1.3 g/day) for 4 days, followed by 650 mg on the morning of day 5. Patients were assessed in‐person at study initiation (day 1) and on days 3 and 5. APAP‐protein adducts and both conventional (alanine aminotransferase) and sensitive (glutamate dehydrogenase [GLDH], full‐length keratin 18 [K18], and total high‐mobility group box 1 protein) biomarkers of liver injury were measured in serum on the mornings of days 1, 3, and 5, with detailed PK analysis of APAP, metabolites, and APAP‐protein adducts throughout day 5. No subject experienced adverse clinical outcomes. GLDH and K18 were significantly different at baseline but did not change in either group during APAP administration. In contrast, clearance of APAP‐protein adducts was dramatically delayed in the cirrhosis group. Minor differences for other APAP metabolites were also detected. Conclusion: Short‐term administration of low‐dose APAP (650 mg twice per day, <1 week) is likely safe in patients with compensated cirrhosis. These data provide a foundation for future studies to test higher doses, longer treatment, and subjects who are decompensated, especially in light of the remarkably delayed adduct clearance in subjects with cirrhosis.

Pharmacokinetics of 2 oral paracetamol formulations in hospitalized octogenarians

AIMS

It is currently unclear how paracetamol should be dosed in order to increase its efficacy while warranting safety in very old adults. The objective was to evaluate the pharmacokinetics of 2 oral paracetamol formulations and its metabolites in hospitalized octogenarians.

METHODS

Geriatric inpatients aged 80 years and older received a 1000-mg paracetamol tablet or granulate at 08.00, 14.00 and 20.00. After at least 4 consecutive gifts, plasma samples were collected around the 08.00 dose (trough, +0.5, +1, +2, +4, +5 and +6 h). Plasma concentrations of paracetamol and its metabolites were determined and individual pharmacokinetic parameters were derived. The Edmonton Frail Scale was used to assess frailty. An analgesic plasma target was defined as an average plasma concentration (C_avg ) of 10 mg/L.

RESULTS

The mean (±standard deviation) age was 86.78 (±4.20) years. The majority (n = 26/36, 72%) received the tablet, 10 (28%) the granulate. Thirty patients (85%) were classified with moderate to severe frailty. Seven (21%) patients had a C_avg above 10 mg/L. The median [interquartile range] time to reach the peak concentration was 50.5 [31.50-92.50] and 42.50 [33.75-106.75] min for the tablet and granulate, respectively. The coefficient of variation was 95% for time to reach the peak concentration and 30% for C_avg of paracetamol. A correlation of C_avg of paracetamol was observed with female sex and total serum bilirubin.

CONCLUSION

Large interindividual differences were found for pharmacokinetic parameters of oral paracetamol in frail inpatients after multiple dosing. Female sex and higher total serum bilirubin concentrations were associated with paracetamol exposure. No significant differences were observed between the tablet and granulate.

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

The Risk of Drug-Drug Interactions with Paracetamol in a Population of Hospitalized Geriatric Patients

Aims

This study investigates the consumption of paracetamol and the risk of potential drug-drug interactions and assesses the clinical impact hereof in patients admitted to a department of geriatric medicine.

Methods

A retrospective and longitudinal study was conducted in patients who had been receiving paracetamol upon or during hospitalization. The hospital files of the included patients were reviewed, including documentation of concomitant medications, diagnoses, biochemical values, and adverse incidents during admission. These parameters were used as a clinical follow-up when assessing a clinical probability impact of the identified drug-drug interactions.

Results

In total, 104 patients were admitted during the study period. 91 (87.5%) of these (mean age 86 years) received a prescription or were treated with paracetamol. Of these, 10% were evaluated as being at risk of potential drug-drug interactions with paracetamol. Seven of the potential drug-drug interactions were related to treatments with warfarin, one with valsartan and one with phenytoin. Of the nine patients at risk, six did experience either abnormal biochemical values or potential related clinical incidents. Four patients experienced increased INR (range 3.2–4.6), of which one patient suffered from anaemia and one with hematemesis. Two patients experienced increased ALAT/ASAT (55/42 U/I and 87/51 U/I, both females). One experienced hypertension.

Conclusion

A large majority of the patients in this study received treatment with paracetamol. Six patients were evaluated as having abnormal biochemical values or were experiencing clinical incidents during their hospitalization potentially related to the identified potential drug-drug interactions.

Population pharmacokinetic modelling of intravenous paracetamol in fit older people displays extensive unexplained variability

AIMS

Paracetamol is the analgesic most used by older people. The physiological changes occurring with ageing influence the pharmacokinetics (PK) of paracetamol and its variability. We performed a population PK-analysis to describe the PK of intravenous (IV) paracetamol in fit older people. Simulations were performed to illustrate target attainment and variability of paracetamol exposure following current dosing regimens (1000 mg every 6 h, every 8 h) using steady-state concentration (Css-mean ) of 10 mg l-1 as target for effective analgesia.

METHODS

A population PK-analysis, using NONMEM 7.2, was performed based on 601 concentrations of paracetamol from 30 fit older people (median age 77.3 years, range [61.8-88.5], body weight 79 kg [60-107]). All had received an IV paracetamol dose of 1000 mg (over 15 min) after elective knee surgery.

RESULTS

A two-compartment PK-model best described the data. Volume of distribution of paracetamol increased exponentially with body weight. Clearance was not influenced by any covariate. Simulations of the standardized dosing regimens resulted in a Css of 9.2 mg l-1 and 7.2 mg l-1 , for every 6 h and every 8 h respectively. Variability in paracetamol PK resulted in Css above 5.4 and 4.1 mg l-1 , respectively, in 90% of the population and above 15.5 and 11.7, respectively, in 10% at these dosing regimens.

CONCLUSIONS

The target concentration was achieved in the average patient with 1000 mg every 6 h, while every 8 h resulted in underdosing for the majority of the population. Furthermore, due to a large (unexplained) interindividual variability in paracetamol PK a relevant proportion of the fit older people remained either under- or over exposed.

Challenges and innovations of drug delivery in older age

Both drug delivery performance and various age-related physical, mental and physiological changes can affect drug effectiveness and safety in elderly patients. The many drug delivery systems developed over the years include recent novel transdermal, nasal, pulmonary and orally disintegrating tablets that provide consistent, precise, timely and more targeted drug delivery. Certain drug delivery systems may be associated with suboptimal outcomes in the elderly because of the nature of drug present, a lack of appreciation of the impact of age-related changes in drug absorption, distribution and clearance, the limited availability of pharmacokinetic, safety and clinical data. Polypharmacy, patient morbidity and poor adherence can also contribute to sub-optimal drug delivery systems outcomes in the elderly. The development of drug delivery systems for the elderly is a poorly realised opportunity, with each system having specific advantages and limitations. A key challenge is to provide the innovation that best meets the specific physiological, psychological and multiple drug requirements of individual elderly patients.

Paracetamol in Older People: Towards Evidence-Based Dosing?

Paracetamol is the most commonly used analgesic in older people, and is mainly dosed according to empirical dosing guidelines. However, the pharmacokinetics and thereby the effects of paracetamol can be influenced by physiological changes occurring with ageing. To investigate the steps needed to reach more evidence-based paracetamol dosing regimens in older people, we applied the concepts used in the paediatric study decision tree. A search was performed to retrieve studies on paracetamol pharmacokinetics and safety in older people (> 60 years) or studies that performed a (sub) analysis of pharmacokinetics and/or safety in older people. Of 6088 articles identified, 259 articles were retained after title and abstract screening. Further abstract and full-text screening identified 27 studies, of which 20 described pharmacokinetics and seven safety. These studies revealed no changes in absorption with ageing. A decreased (3.9-22.9%) volume of distribution (Vd) in robust older subjects and a further decreased Vd (20.3%) in frail older compared with younger subjects was apparent. Like Vd, age and frailty decreased paracetamol clearance (29-45.7 and 37.5%) compared with younger subjects. Due to limited and heterogeneous evidence, it was difficult to draw firm and meaningful conclusions on changed risk for paracetamol safety in older people. This review is a first step towards bridging knowledge gaps to move to evidence-based paracetamol dosing in older subjects. Remaining knowledge gaps are safety when using therapeutic dosages, pharmacokinetics changes in frail older people, and to what extent changes in paracetamol pharmacokinetics should lead to a change in dosage in frail and robust older people.

Are some people at increased risk of paracetamol-induced liver injury? A critical review of the literature

Purpose

Paracetamol is one of the world’s most commonly used drugs. In overdose, it is well established to be hepatotoxic. The aim of this review was to identify factors that have been, or actually are, associated with the development of liver injury after paracetamol exposure in humans.

Method

Google Scholar and PubMed were searched on various dates between December 2016 and March 2017. Papers identified had their references analysed for further studies that might be relevant.

Results

At the time of writing, there was little good quality clinical evidence—from studies of paracetamol overdose or therapeutic use—to suggest that any groups of people are relatively protected from, or are at greater risk of, liver injury. The factors that were historically used to indicate higher risk in the UK have no good quality clinical evidence to support their re-introduction into clinical practice. The safe (and still effective) oral dose of paracetamol in patients weighing less than 50 kg has not been established.

Conclusion

There is no patient group that is unequivocally at elevated risk of paracetamol-induced liver toxicity. We propose two clinical scenarios that warrant further research. Firstly, there is a need to establish whether the dose of paracetamol should be reduced in patients with low body weight. Secondly, if or when genomic information regarding individual patients becomes readily available to inform prescribing, we propose the contribution of the genome to paracetamol toxicity should be re-investigated with robustly designed studies. Such studies could enhance the safe use of one of the most frequently taken drugs.

Electronic supplementary material

The online version of this article (10.1007/s00228-017-2356-6) contains supplementary material, which is available to authorized users.

Can paracetamol (acetaminophen) be administered to patients with liver impairment?

Although 60 years have passed since it became widely available on the therapeutic market, paracetamol dosage in patients with liver disease remains a controversial subject. Fulminant hepatic failure has been a well documented consequence of paracetamol overdose since its introduction, while short and long term use have both been associated with elevation of liver transaminases, a surrogate marker for acute liver injury. From these reports it has been assumed that paracetamol use should be restricted or the dosage reduced in patients with chronic liver disease. We review the factors that have been purported to increase risk of hepatocellular injury from paracetamol and the pharmacokinetic alterations in different pathologies of chronic liver disease which may affect this risk. We postulate that inadvertent under-dosing may result in concentrations too low to enable efficacy. Specific research to improve the evidence base for prescribing paracetamol in patients with different aetiologies of chronic liver disease is needed.

Anesthesia for the elderly outpatient

PURPOSE OF REVIEW

As the number of ambulatory surgery procedures continues to grow in an aging global society, the implementation of evidence-based perioperative care programs for the elderly patients will assume increased importance.

RECENT FINDINGS

Increasing evidence supports the expanded use of ambulatory surgery for managing elderly patients undergoing elective surgery procedures.

SUMMARY

This review article describes the demographics of ambulatory surgery in the elderly population. This review article describes the effects of aging on the responses of geriatric patients to anesthetic and analgesic drugs used during ambulatory surgery. Important considerations in the preoperative evaluation of elderly outpatients with co-existing diseases, as well as the advantages and disadvantages of different anesthetic techniques on a procedural-specific basis, and recommendations regarding the management of common postoperative side-effects (including delirium and cognitive dysfunction, fatigue, dizziness, pain, and gastrointestinal dysfunction) after ambulatory surgery. Finally, we discuss the future challenges related to the continued expansion of ambulatory surgery practice in this growing segment of our surgical population. The role of anesthesiologists as perioperative physicians is of critical importance for optimizing surgical outcomes for elderly patients undergoing ambulatory surgery. Providing high-quality, evidence-based anesthetic and analgesic care for elderly patients undergoing elective operations on an ambulatory basis will assume greater importance in the future.

Perioperative management of elderly patients

The older population only represents 13.7% of the US population but has grown by 21% since 2002. The centenarian population is growing at a faster rate than the total US population. This unprecedented growth has significantly increased surgical demand. The establishment of quality and performance improvement data has allowed researchers to focus attention on the older patient population, resulting in an exponential increase in studies. Although there is still much work to be done in this field, overlying themes regarding the perioperative management of elderly patients are presented in this article based on a thorough literature review.

Covariates of intravenous paracetamol pharmacokinetics in adults

BACKGROUND

Pharmacokinetic estimates for intravenous paracetamol in individual adult cohorts are different to a certain extent, and understanding the covariates of these differences may guide dose individualization. In order to assess covariate effects of intravenous paracetamol disposition in adults, pharmacokinetic data on discrete studies were pooled.

METHODS

This pooled analysis was based on 7 studies, resulting in 2755 time-concentration observations in 189 adults (mean age 46 SD 23 years; weight 73 SD 13 kg) given intravenous paracetamol. The effects of size, age, pregnancy and other clinical settings (intensive care, high dependency, orthopaedic or abdominal surgery) on clearance and volume of distribution were explored using non-linear mixed effects models.

RESULTS

Paracetamol disposition was best described using normal fat mass (NFM) with allometric scaling as a size descriptor. A three-compartment linear disposition model revealed that the population parameter estimates (between subject variability,%) were central volume (V1) 24.6 (55.5%) L/70 kg with peripheral volumes of distribution V2 23.1 (49.6%) L/70 kg and V3 30.6 (78.9%) L/70 kg. Clearance (CL) was 16.7 (24.6%) L/h/70 kg and inter-compartment clearances were Q2 67.3 (25.7%) L/h/70 kg and Q3 2.04 (71.3%) L/h/70 kg. Clearance and V2 decreased only slightly with age. Sex differences in clearance were minor and of no significance. Clearance, relative to median values, was increased during pregnancy (F(PREG) = 1.14) and decreased during abdominal surgery (F(ABDCL) = 0.715). Patients undergoing orthopaedic surgery had a reduced V2 (F(ORTHOV) = 0.649), while those in intensive care had increased V2 (F(ICV) = 1.51).

CONCLUSIONS

Size and age are important covariates for paracetamol pharmacokinetics explaining approximately 40% of clearance and V2 variability. Dose individualization in adult subpopulations would achieve little benefit in the scenarios explored.

Sources of interindividual variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in other individuals. A major source of this variability in drug response is drug metabolism, where differences in pre-systemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C max, and/or C min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is well recognized that both intrinsic (such as genetics, age, sex, and disease states) and extrinsic (such as diet, chemical exposures from the environment, and even sunlight) factors play a significant role. For the family of cytochrome P450 enzymes, the most critical of the drug metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, up- and down-regulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less reliably predictable and time-dependent manner. Understanding the mechanistic basis for drug disposition and response variability is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that brings with it true improvements in health outcomes in the therapeutic treatment of disease.

Adverse effects of analgesics commonly used by older adults with osteoarthritis: focus on non-opioid and opioid analgesics

BACKGROUND

Osteoarthritis (OA) is the most common cause of disability in older adults, and although analgesic use can be helpful, it can also result in adverse drug events.

OBJECTIVE

To review the recent literature to describe potential adverse drug events associated with analgesics commonly used by older adults with OA.

METHODS

To identify articles for this review, a systematic search of the English-language literature from January 2001 to June 2012 was conducted using PubMed, MEDLINE, EBSCO, and the Cochrane Database of Systematic Reviews for publications related to the medical management of OA. Search terms used were "analgesics," "acetaminophen," "nonsteroidal anti-inflammatory drugs" (NSAIDs), "opioids," "pharmacokinetics," "pharmacodynamics," and "adverse drug events." The search was restricted to those articles that concerned humans aged ≥65 years. A manual search of the reference lists from identified articles and the authors' article files, book chapters, and recent reviews was conducted to identify additional articles. From these, the authors identified those studies that examined analgesic use in older adults.

RESULTS

There are limited data to suggest that non-frail elders are more likely than their younger counterparts to develop acetaminophen-induced hepatotoxicity. However, decreased hepatic phase II metabolism in frail elders may result in increased risk of hepatotoxicity. It is now well established that older adults are at higher risk of NSAID-induced gastrointestinal toxicity and renal insufficiency. Insofar as opioids, the data that suggest an increased risk of falls, fractures, or delirium need to be tempered by the potential risk of inadequately treating severe chronic OA-related pain.

CONCLUSIONS

Acetaminophen is the mainstay frontline analgesic for treating OA-related pain in older adults. NSAIDs should be limited to short-term use only, and for moderate to severe OA-related pain, opioids may be preferable in individuals without substance abuse or dependence issues.

Use of antiarrhythmic drugs in elderly patients

Human aging is a global issue with important implications for current and future incidence and prevalence of health conditions and disability. Cardiac arrhythmias, including atrial fibrillation, sudden cardiac death, and bradycardia requiring pacemaker placement, all increase exponentially after the age of 60. It is important to distinguish between the normal, physiological consequences of aging on cardiac electrophysiology and the abnormal, pathological alterations. The age-related cardiac changes include ventricular hypertrophy, senile amyloidosis, cardiac valvular degenerative changes and annular calcification, fibrous infiltration of the conduction system, and loss of natural pacemaker cells and these changes could have a profound effect on the development of arrhythmias. The age-related cardiac electrophysiological changes include up- and down-regulation of specific ion channel expression and intracellular Ca(2+) overload which promote the development of cardiac arrhythmias. As ion channels are the substrates of antiarrhythmic drugs, it follows that the pharmacokinetics and pharmacodynamics of these drugs will also change with age. Aging alters the absorption, distribution, metabolism, and elimination of antiarrhythmic drugs, so liver and kidney function must be monitored to avoid potential adverse drug effects, and antiarrhythmic dosing may need to be adjusted for age. Elderly patients are also more susceptible to the side effects of many antiarrhythmics, including bradycardia, orthostatic hypotension, urinary retention, and falls. Moreover, the choice of antiarrhythmic drugs in the elderly patient is frequently complicated by the presence of co-morbid conditions and by polypharmacy, and the astute physician must pay careful attention to potential drug-drug interactions. Finally, it is important to remember that the use of antiarrhythmic drugs in elderly patients must be individualized and tailored to each patient's physiology, disease processes, and medication regimen.

Safety and efficacy of intravenous acetaminophen in the elderly after major orthopedic surgery: subset data analysis from 3, randomized, placebo-controlled trials

As the number of patients aged 65 years and older increases, joint replacement has become a frequent procedure after progressive osteoarthritis or fractures. Although hip and knee arthroplasty has become a relatively commonplace procedure in this age-group, the advanced age in patients undergoing these procedures often is associated with comorbidities and potential complications that can present challenges and limit analgesic choices. This subset analysis is designed to determine the efficacy and safety of intravenous (IV) acetaminophen in the elderly subpopulation from 3 placebo-controlled studies conducted to document the safety and efficacy of IV acetaminophen. A total of 231 patients were enrolled in the 3 trials, and of these, a total of 107 patients (46%) were aged 65 years or older. Across the studies, safety and efficacy were well documented in the elderly subpopulation and were comparable with the subpopulation younger than 65 years. A review of the literature similarly demonstrates the efficacy and safety of IV acetaminophen used for postoperative analgesia after joint replacement.

Perioperative care for the older outpatient undergoing ambulatory surgery

As the number of ambulatory surgery procedures continues to grow in an aging global society, the implementation of evidence-based perioperative care programs for the elderly will assume increased importance. Given the recent advances in anesthesia, surgery, and monitoring technology, the ambulatory setting offers potential advantages for elderly patients undergoing elective surgery. In this review article we summarize the physiologic and pharmacologic effects of aging and their influence on anesthetic drugs, the important considerations in the preoperative evaluation of elderly outpatients with coexisting diseases, the advantages and disadvantages of different anesthetic techniques on a procedural-specific basis, and offer recommendations regarding the management of common postoperative side effects (including delirium and cognitive dysfunction, fatigue, dizziness, pain, and gastrointestinal dysfunction) after ambulatory surgery. We conclude with a discussion of future challenges related to the growth of ambulatory surgery practice in this segment of our surgical population. When information specifically for the elderly population was not available in the peer-reviewed literature, we drew from relevant information in other ambulatory surgery populations.

Therapeutic paracetamol treatment in older persons induces dietary and metabolic modifications related to sulfur amino acids

Sulfur amino acids are determinant for the detoxification of paracetamol (N-acetyl-p-aminophenol) through sulfate and glutathione conjugations. Long-term paracetamol treatment is common in the elderly, despite a potential cysteine/glutathione deficiency. Detoxification could occur at the expense of anti-oxidative defenses and whole body protein stores in elderly. We tested how older persons satisfy the extra demand in sulfur amino acids induced by long-term paracetamol treatment, focusing on metabolic and nutritional aspects. Effects of 3 g/day paracetamol for 14 days on fasting blood glutathione, plasma amino acids and sulfate, urinary paracetamol metabolites, and urinary metabolomic were studied in independently living older persons (five women, five men, mean (±SEM) age 74 ± 1 years). Dietary intakes were recorded before and at the end of the treatment and ingested sulfur amino acids were evaluated. Fasting blood glutathione, plasma amino acids, and sulfate were unchanged. Urinary nitrogen excretion supported a preservation of whole body proteins, but large-scale urinary metabolomic analysis revealed an oxidation of some sulfur-containing compounds. Dietary protein intake was 13% higher at the end than before paracetamol treatment. Final sulfur amino acid intake reached 37 mg/kg/day. The increase in sulfur amino acid intake corresponded to half of the sulfur excreted in urinary paracetamol conjugates. In conclusion, older persons accommodated to long-term paracetamol treatment by increasing dietary protein intake without any mobilization of body proteins, but with decreased anti-oxidative defenses. The extra demand in sulfur amino acids led to a consumption far above the corresponding population-safe recommendation.

A review of the evidence concerning hepatic glutathione depletion and susceptibility to hepatotoxicity after paracetamol overdose

Paracetamol (acetaminophen) poisoning is common throughout the world. The management of nonstaggered (acute) paracetamol overdose is based on the plasma paracetamol concentration plotted on a treatment nomogram. In the UK there are two treatment lines on this nomogram, with the lower treatment line used for individuals felt to be at ‘high risk’ of paracetamol-related hepatotoxicity either as a result of induction of cytochrome P450 isoenzymes or reduction of intrahepatic glutathione. In this article we review the risk factors that, in current guidelines, are felt to increase risk due to a reduction in intrahepatic glutathione concentrations. Based on our review of the published literature, we feel that cystic fibrosis, acute viral illness, malnutrition, and eating disorders such as anorexia nervosa are likely to be associated with reduction in intrahepatic glutathione concentrations, and that this risk is likely to be related to malnutrition secondary to the disease. Chronic hepatitis C infection is also associated with reduced glutathione concentrations, although this appears to be independent of any associated malnutrition. Ageing and acute fasting are not associated with an increased risk of paracetamol-related hepatotoxicity due to reductions in glutathione concentrations. Finally, the evidence for HIV infection is inconclusive, particularly as the majority of studies were conducted in the pre-anti-viral treatment (HAART) era; however it is likely that patients with symptomatic HIV/AIDS have reduced glutathione concentrations due to associated malnutrition. Although there have been few studies which have specifically investigated whether there is an association between reduced intrahepatic glutathione concentrations and increased risk of paracetamol-related hepatotoxicity, in our opinion, it is likely that the above conditions that are associated with reduced glutathione concentrations, will be associated with an increased risk of paracetamol-related hepatotoxicity.

Acute postoperative pain management in the older patient

Acute pain management in the older adult is both challenging and rewarding. This review addresses the difficulty with assessment of pain in the older adult, variations in the pain experience of older adults, physiological differences between the young and old, changes in pharmacokinetics and pharmacodynamics with age, and useful pharmacological treatments for acute pain in older adults. It then presents a few representative cases of pain management in older adults. The goal of this review is to provide relevant information that can be used to manage acute postoperative pain in the older adult.

Pharmacokinetics of intravenous paracetamol in elderly patients

BACKGROUND AND OBJECTIVES

Intravenous paracetamol (N-acetyl-paraminophenol, acetaminophen) is a widely used nonopioid analgesic which has become popular in the treatment of pain in many patient groups, including the elderly. Although intravenous paracetamol has been studied widely in clinical analgesia studies, there is little information on its pharmacokinetics in the elderly. We designed this study to determine the pharmacokinetics of intravenous paracetamol in very old patients and to compare them with that of younger patients. We also considered the effect of adenosine triphosphate-binding cassette G2 protein (ABCG2) genotype and renal function on paracetamol pharmacokinetics in these patients.

METHODS

We compared the pharmacokinetics of intravenous paracetamol in four groups of ten patients, aged 20-40, 60-70, 70-80 and 80-90 years, undergoing orthopaedic surgery. Paracetamol 1000 mg was given by infusion over 15 minutes. Plasma concentrations of paracetamol and its glucuronide and sulphate conjugates were measured for 24 hours with a high-performance liquid chromatographic method and ABCG2 genotype was determined. Glomerular filtration rate (GFR) was estimated from age, sex and serum creatinine of the patient.

RESULTS

In the group aged 80-90 years, the mean value of the area under the plasma concentration-time curve extrapolated to infinity (AUC(∞)) of paracetamol was 54-68% higher than in the two youngest groups. Paracetamol clearance showed a statistically significant dependence on age group, whereas volume of distribution during elimination and elimination half-life were associated with age group and sex, respectively. Based on mean AUC(∞) of paracetamol glucuronide and paracetamol sulphate, the oldest patients had 1.3- to 1.5-fold greater exposure to these metabolites than patients aged 20-40 years. ABCG2 genotype did not affect paracetamol pharmacokinetics. There was a linear correlation between the values of AUC(∞) of paracetamol, its glucuronide and sulphate metabolites and GFR.

CONCLUSION

Age and sex are important factors affecting the pharmacokinetics of paracetamol. The higher the age of the patient, the higher is the exposure to paracetamol. Female sex is associated with increased paracetamol concentrations but ABCG2 genotype does not seem to affect paracetamol pharmacokinetics. Trial registration number (EudraCT): 2006-001917-14.

Clinical implications of changes in hepatic drug metabolism in older people

Prescribing for older people is challenging because of the paucity of clinical trial evidence of therapeutic benefit in this population and the presence of evidence that older people are at increased risk of adverse drug reactions. The outcomes of pharmacotherapies in older people depend on age-related changes in both pharmacokinetics and pharmacodynamics. Of the pharmacokinetic changes, those in hepatic metabolism are the most significant. Recent advances in biogerontology have improved our understanding of changes that occur in hepatic pharmacokinetics in older people. Knowledge of age-related changes in hepatic metabolism can guide prescribing and help reduce the risk–benefit ratio of using medications in older people.

Clinical pharmacology of analgesic medicines in older people: impact of frailty and cognitive impairment

Pain is highly prevalent in frail older people who often have multiple co-morbidities and multiple medicines. Rational prescribing of analgesics in frail older people is complex due to heterogeneity in drug disposition, comorbid medical conditions, polypharmacy and variability in analgesic response in this population. A critical issue in managing older people with pain is the need for judicious choice of analgesics based on a comprehensive medical and medication history. Care is needed in the selection of analgesic medicine to avoid drug-drug or drug-disease interactions. People living with dementia and cognitive impairment have suboptimal pain relief which in part may be related to altered pharmacodynamics of analgesics and challenges in the systematic assessment of pain intensity in this patient group. In the absence of rigorously controlled trials in frail older people and those with cognitive impairment a pharmacologically-guided approach can be used to optimize pain management which requires a systematic understanding of the pharmacokinetics and pharmacodynamics of analgesics in frail older people with or without changes in cognition.

Effects of imatinib mesylate on the pharmacokinetics of paracetamol (acetaminophen) in Korean patients with chronic myelogenous leukaemia

AIMS

The major objective of the present study was to investigate the effect of imatinib on the pharmacokinetics of paracetamol in patients with chronic myelogenous leukaemia (CML).

METHODS

Patients (n = 12) received a single oral dose of acetaminophen 1000 mg on day 1 (control). On days 2-8, imatinib 400 mg was administered daily. On day 8 (treatment), another 1000 mg dose of paracetamol was administered 1 h after the morning dose of imatinib 400 mg. Blood and urine samples were collected for bioanalytical analyses.

RESULTS

The area under the plasma concentration-time curve (AUC) for paracetamol, paracetamol glucuronide and paracetamol sulphate under control conditions was similar to that after treatment with imatinib; the 90% confidence interval of the log AUC ratio was within 0.8 to 1.25. Urinary excretion of paracetamol, paracetamol glucuronide and paracetamol sulphate was also unaffected by imatinib. The pharmacokinetics of paracetamol and imatinib in Korean patients with CML were similar to previous pharmacokinetic results in white patients with CML. Co-administration of a single dose of paracetamol and multiple doses of imatinib was well tolerated and safety profiles were similar to those of either drug alone.

CONCLUSIONS

The pharmacokinetics of paracetamol and its major metabolites in the presence of imatinib were similar to those of the control conditions and the combination was well tolerated. These findings suggest that imatinib can be safely administered with paracetamol without dose adjustment of either drug.

The elderly patient and postoperative pain treatment

The management of postoperative pain in elderly patients can be a difficult task. Older patients have co-existing diseases and concurrent medications, diminished functional status and physiological reserve and age-related pharmacodynamic and pharmacokinetic changes. Pain assessment presents numerous problems arising from differences in reporting cognitive impairment and difficulties in measurement. The elderly are also at higher risk of adverse consequences from surgery and unrelieved or undertreated pain. Selection of analgesic therapy needs to balance the potential efficacy with the incidence of interactions, complications or side effects in the post-operative period. Drug titration in the post-anaesthesia care unit should be encouraged together with analgesia on request in the wards. Multimodal analgesia, using acetaminophen, non-steroidal anti-inflammatory drugs or other non opioid drugs, is the best way to decrease opioid consumption and thus opioid-related adverse events. Sophisticated analgesic methods like PCA, regional analgesia and PCEA are not contraindicated in the elderly but pain relief and side effects should be monitored.

Drug dosage in the elderly: dermatological drugs

Drug pharmacokinetics and pharmacodynamics may be altered in the elderly. An important contribution is made by decreased renal function, but biotransformation in the liver may also play a role. Commonly prescribed dermatological drugs such as methotrexate and cetirizine are likely to be eliminated more slowly in the elderly and potentially hepatotoxic drugs such as itraconazole and acitretin should be used with caution. Altered drug distribution as a result of body composition changes can lead to prolonged half-life or higher plasma concentrations of many drugs. Higher prevalence of adverse drug reactions and multidrug regimens, and large interindividual variability in drug response make drug dosage and administration in the elderly challenging. New immunobiological agents such as alefacept, efalizumab and etanercept, which are approved for treatment of psoriasis, seem to be as well tolerated in the elderly as in younger patients. A recommended approach when prescribing drugs to the elderly would be to start with a small initial dose and to reduce the number of drugs administered simultaneously. It is crucial to simplify the drug regimen as much as possible in order to enhance drug management in the elderly. To improve pharmacotherapy in the elderly, we review age-related changes in pharmacokinetics that are likely to play a role in dermatological practice.

Efficacy and safety of over-the-counter analgesics in the treatment of common cold and flu

RATIONALE

Common cold and flu are the most common human illnesses, and over-the-counter (OTC) analgesics are widely used to treat the pain and fever symptoms. Despite the every day use of these analgesic there is little information available in the literature on the efficacy and safety of these medicines in treating colds and flu symptoms. The aim of this review was to determine the safety and efficacy of the analgesics, aspirin, paracetamol and aspirin for the treatment of colds and flu.

METHODS

Electronic databases and a personal database were searched and the information retrieved together with information from relevant textbooks has been integrated in the review.

RESULTS

The literature search established that there is relatively little information on the use of analgesics in treating colds and flu and that much of the safety and efficacy data must be related to other pain and fever models. The review establishes that aspirin, paracetamol and ibuprofen are safe in OTC doses and that there is no evidence for any difference between the medicines as regards efficacy and safety for treatment of colds and flu (except in certain cases such as the use of aspirin in feverish children). There is also no evidence that these medicines prolong the course of colds and flu by any effect on the immune system or by reducing fever.

CONCLUSION

Despite the lack of clinical data on the safety and efficacy of analgesics for the treatment of colds and flu symptoms a case can be made that these medicines are safe and effective for treatment of these common illnesses.

The Therapeutic Use of Acetaminophen in Patients with Liver Disease

Acetaminophen has been used safely and effectively for many years to manage pain and/or fever in patients of all ages. It is commonly recommended as first-line therapy for a variety of patients and conditions, including the elderly, children with viral illnesses, and patients with osteoarthritis, gastrointestinal conditions, bleeding disorders, cardiovascular disease, or renal disease. However, its use is often avoided in patients with chronic liver disease. The perception that acetaminophen should be avoided in such patients arose from awareness of the association between massive acetaminophen overdose and hepatotoxicity, combined with a lack of understanding of the metabolism of acetaminophen in patients with liver disease. There are various theoretical mechanisms of acetaminophen hepatotoxicity in chronic liver disease including: altered metabolism and depleted glutathione stores that would be expected to increase accumulation of the hepatotoxic intermediate, N-acetyl-p-benzoquinone imine (NAPQI). Available studies in patients with chronic liver disease, however, have shown that although the half-life of acetaminophen may be prolonged, cytochrome P-450 activity is not increased and glutathione stores are not depleted to critical levels in those taking recommended doses. Furthermore, acetaminophen has been studied in a variety of liver diseases without evidence of increased risk of hepatotoxicity at currently recommended doses. Therefore, acetaminophen can be used safely in patients with liver disease and is a preferred analgesic/antipyretic because of the absence of the platelet impairment, gastrointestinal toxicity, and nephrotoxicity associated with nonsteroidal antiinflammatory drugs.

Cardiovascular Drug Therapy in Elderly Patients

An increasing number of elderly patients are exposed to cardiovascular drugs for the treatment of acute and/or chronic conditions. This is a result of the progressive aging of the population, a common feature in most industrialised countries, and an improvement in primary and secondary cardiovascular prevention strategies with increased survival rates. Traditionally, most elderly patients receiving cardiovascular drugs had advanced cardiac, liver and kidney disease that significantly influenced drug pharmacokinetic and pharmacodynamic parameters. Currently, however, many patients without significant organ impairment receive cardiovascular therapy for primary or early secondary prevention (i.e. increased vascular risk, asymptomatic left ventricular dysfunction, poststroke phase, type 2 diabetes mellitus), highlighting the need for a better understanding of specific age-related pharmacokinetic and pharmacodynamic effects. A systematic review has been conducted on the specific effects of aging, in the absence of major co-morbidities, on the pharmacokinetic and pharmacodynamic properties of traditional and newer cardiovascular drugs. Currently, the evidence available is poor or nonexisting for several drugs and mainly derived from very small and underpowered studies, thus limiting data interpretation. In particular, there is very little information on patients >80 years of age, thus raising important concerns about the correct use of these drugs in this constantly growing population.

Human variability for metabolic pathways with limited data (CYP2A6, CYP2C9, CYP2E1, ADH, esterases, glycine and sulphate conjugation)

Human variability in the kinetics of a number of phase I (CYP2A6, CYP2C9, CYP2E1, alcohol dehydrogenase and hydrolysis) and phase II enzymes (glycine and sulphate conjugation) was analysed using probe substrates metabolised extensively (>60%) by these routes. Published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and available data on subgroups of the population (effects of ethnicity, age and disease) were abstracted using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration time-curve (AUC)] and acute exposure (C(max)). Interindividual differences in kinetics for all these pathways were low in healthy adults ranging from 21 to 34%. Pathway-related uncertainty factors to cover the 95th, 97.5th and 99th centiles of healthy adults were derived for each metabolic route and were all below the 3.16 kinetic default uncertainty factor in healthy adults, with the possible exception of CYP2C9*3/*3 poor metabolisers (based on a very limited number of subjects). Previous analyses of other pathways have shown that neonates represent the most susceptible subgroup and this was true also for glycine conjugation for which an uncertainty factor of 29 would be required to cover 99% of this subgroup. Neonatal data were not available for any other pathway analysed.

Age-related changes in pharmacokinetics and pharmacodynamics: basic principles and practical applications

Advancing age is characterized by impairment in the function of the many regulatory processes that provide functional integration between cells and organs. Therefore, there may be a failure to maintain homeostasis under conditions of physiological stress. The reduced homeostatic ability affects different regulatory systems in different subjects, thus explaining at least partly the increased interindividual variability occurring as people get older. Important pharmacokinetic and pharmacodynamic changes occur with advancing age. Pharmacokinetic changes include a reduction in renal and hepatic clearance and an increase in volume of distribution of lipid soluble drugs (hence prolongation of elimination half-life) whereas pharmacodynamic changes involve altered (usually increased) sensitivity to several classes of drugs such as anticoagulants, cardiovascular and psychotropic drugs. This review focuses on the main age-related physiological changes affecting different organ systems and their implications for pharmacokinetics and pharmacodynamics of drugs.

Paracetamol and metabolite pharmacokinetics in infants

BACKGROUND

Data concerning metabolism of paracetamol in infants are scant. Previous studies have examined urinary metabolite recovery rates after a single dose of paracetamol in either neonates (<6 weeks) or children (3-9 years). There are no studies investigating infants.

METHODS

Infants ( n=47) undergoing major craniofacial surgery were given paracetamol 19-45 mg/kg 6-, 8-, or 12-hourly as either elixir or suppository formulation for postoperative analgesia, after a loading dose of 33-59 mg/kg rectally during the operation. Serum was assayed for paracetamol concentration in 40 of these infants at 5, 8, 11, 14, 17 and 20 h postoperatively. Urine samples were collected every 3 h for 24 h in 15 of these infants. The clearances of paracetamol to glucuronide and sulphate metabolites as well as the urinary clearance of unmetabolised paracetamol were estimated using non-linear, mixed-effects models.

RESULTS

Mean (+/-SD) age and weight of the patients were 11.8+/-2.5 months and 9.1+/-1.9 kg. Clearances of paracetamol to paracetamol-glucuronide (%CV) and to paracetamol-sulphate were 6.6 (11.5) l/h and 7.5 (11.5) l/h respectively, standardised to a 70-kg person using allometric "1/4 power" models. Glucuronide formation clearance, but not sulphate formation, was related to age and increased with age from a predicted value in a neonate of 2.73 l/h/70 kg to a mature value of 6.6 l/h/70 kg with a maturation half-life of 8.09 months. Urine clearance of paracetamol-glucuronide, paracetamol-sulphate and unchanged paracetamol (%CV) were, respectively, 2.65, 3.03 and 0.55 (28) l/h/70 kg. The urine clearance of unchanged paracetamol and metabolites was related to urine volume flow rate. Clearance attributable to pathways other than these measured in urine was not identifiable. The glucuronide/sulphate formation clearance ratio was 0.69 at 12 months of age. Sulphate metabolism contributed 50% towards paracetamol clearance.

CONCLUSION

Glucuronide formation clearance increases with age in the infant age range but sulphate formation does not. Renal clearance of paracetamol and its metabolites increases with urine flow rate. This and other studies show that paracetamol metabolism to glucuronide appears to be similar in infants and children, but in adults is increased in comparison with children. Oxidative pathways were undetectable in this infant study and may explain, in part, the reduced incidence of hepatotoxicity in infants.

Human variability in glucuronidation in relation to uncertainty factors for risk assessment

The appropriateness of the default uncertainty factor for human variability in kinetics has been investigated for glucuronidation using an extensive database of substrates metabolised primarily by this pathway. Inter-individual variability was quantified for 15 compounds from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating to chronic exposure (metabolic and total clearances, area under the plasma concentration time-curve (AUC)) and acute exposure (C(max)). Low inter-individual variability (about 30-35%) was found for all parameters (clearance corrected or not corrected for body weight, metabolic clearance, oral AUC and C(max)) after either iv or oral administration to healthy adults. The overall variability of 31% for glucuronidation in healthy adults supported the validity of the default kinetic uncertainty factor of 3.16 for this group, because it would cover more than 99% of individuals. Comparisons between potentially sensitive subgroups and healthy adults using differences in means and variability indicated that neonates showed the greatest impairment of glucuronidation, and that the 3.16 kinetic default factor applied to the mean data for adults would be inadequate for this subpopulation. The in vivo data have been used to derive pathway-related default factors for compounds eliminated largely via glucuronidation.

Drug metabolism and drug interactions in the elderly

In the elderly concomitant use of several drugs (polypharmacy) is very common. Thus, the risk for drug interactions might be increased in this population. Since most drugs are hepatically eliminated by various metabolic pathways, liver function has to be considered as an additional factor modifying drug response. This chapter focuses on the hepatic mechanisms of interactions, especially on various inhibitors and inducers of the most important cytochrome P450 isoenzymes involved in drug metabolism. In addition, age-dependent changes in liver function are addressed. Based on pharmacokinetic results with different probe drugs, some inconsistencies in this area are discussed. The most important metabolic drug-drug interactions are independent of the age of the patients. However, since elderly patients consume a greater proportional share of drugs, they represent a population at risk for interactions. Awareness of this clinical problem may help to diminish those risks.

Glutathione monoethyl ester protects against glutathione deficiencies due to aging and acetaminophen in mice

Our previous results indicated that glutathione (GSH) and/or cysteine (Cys) deficiency occurs in many aging tissues and also after acetaminophen (APAP) administration. The aim of this study was to investigate whether GSH monoethyl ester (GSH-OEt) can correct these deficiencies. Mice of different ages (3-31 months) through the life span were sacrificed 2 h after i.p. injection of GSH-OEt (10 mmol/kg). In separate experiments, old mice (30-31 months) received the same dose of ester 30 min before the administration of APAP (375 mg/kg) or buthionine sulfoximine (BSO, 4 mmol/kg), an inhibitor of GSH synthesis. Liver and kidney samples were analyzed for GSH and Cys by HPLC. The hepatic GSH and renal cortical GSH and Cys concentrations were about 30% lower in old mice (30-31 months) compared to mature mice (12 months). GSH-OEt corrected these aging-related decreases. APAP decreased both hepatic and renal cortical GSH and Cys concentrations in old mice, but GSH-OEt prevented these decreases. GSH-OEt also prevented the BSO-induced decreases in hepatic and renal GSH concentrations. The results demonstrated that GSH-OEt protected against GSH deficiency due to biological aging as well as APAP-induced decreases in old mice.

Paracetamol metabolism in patients with ulcerative colitis

AIMS

The capacity for sulphation of phenols appears to be impaired in the colonic mucosa of patients with ulcerative colitis. The aim of the present study was to investigate the systemic capacity for sulphation of phenols in patients with ulcerative colitis assessed by the metabolic clearances of paracetamol to the sulphate, glucuronide and glutathione derived metabolites.

METHODS

Ten patients with ulcerative colitis and 10 control subjects received a single oral dose of paracetamol (1 g). Venous blood samples were collected frequently for pharmacokinetic determinations (one compartment model). Urine was collected for 24 h. Plasma samples were analysed for parent drug and urine samples for parent drug and metabolites by h.p.l.c. Partial metabolic clearances were calculated as the fractional urinary recovery of each conjugate multiplied by the apparent oral clearance of paracetamol.

RESULTS

The apparent oral clearance of paracetamol and the partial clearances of its metabolites were not significantly different between the two study groups. Median value and the corresponding 25th and 75th percentiles for the clearance of the sulphate metabolites were 93.6 (82.5-138.8) ml kg(-1)h(-1) and 77.4 (75.5-99.1), patients with ulcerative colitis and control subjects, respectively.

CONCLUSIONS

These results do not indicate a general impairment of the systemic capacity for sulphation of paracetamol in patients with ulcerative colitis.

Prediction of acetaminophen concentrations in overdose patients using a Bayesian pharmacokinetic model

A pharmacokinetic program using population-based parameter estimates and a Bayesian forecasting model was retrospectively evaluated for predicting acetaminophen serum concentrations in overdose patients. Dynamic disposition factors known to affect acetaminophen disposition (emesis, activated charcoal, N-acetylcysteine, etc.) were included in the program. Twenty six patients who reported an acetaminophen ingestion of at least 70 mg/kg within 24 h of presentation to the hospital and had at least one measured acetaminophen concentration were included. Prediction of initial acetaminophen concentrations using only population-based parameter estimates resulted in a percent mean error (%ME) and percent mean absolute error (%MAE) of 9.3 and 42.2, respectively. Using only the initial concentration as feedback, the Bayesian forecasting model accurately predicted the second acetaminophen concentration (%ME = 4.0, %MAE = 23.6). The Bayesian model also accurately predicted all concentrations within 8 h of the ingestion (%ME = 10.6, %MAE = 24.0). The prediction of concentrations between 2 to 4 h and 4 to 4.5 h after ingestion with only population-based parameter estimates resulted in %ME of 17.0 and 13.2, respectively, and %MAE of 36.5 and 35.1, respectively. Our data suggests that acetaminophen serum concentrations occurring within the first 4.5 h after ingestion can be reliably predicted by the set of population-based parameter estimates evaluated. Once a single acetaminophen concentration is available, the Bayesian forecasting model can accurately predict subsequent concentrations within the first 8 h after an acetaminophen ingestion.

Age, environmental factors and drug metabolism

Both ageing and the environment have a significant impact on xenobiotic metabolism. Furthermore, there is some evidence from in vivo studies that the elderly respond to environmental changes to a lesser degree than younger individuals. This article reviews the available evidence and concentrates on possible underlying mechanisms.

Factors and conditions affecting the glucuronidation of oxazepam

The aim of the present work was to investigate the impact of disease states and environmental and host factors on the glucuronidation of oxazepam. Glucuronidation represents quantitatively one of the most important metabolic conjugation pathways (phase II) in man for the inactivation and detoxication of xenobiotics and endogenous compounds and the liver is the major site for it to take place. Far less attention has been paid to the conjugation reactions in previous clinical research in this field compared to the immense interest in the oxidative biotransformation pathways (phase I). This fact is mainly due to the latter giving rise to active or reactive metabolites with a toxicological potential. The metabolism of oxazepam expresses exclusively the capacity for glucuronide formation. It was a prerequisite to establish the bioavailability of oxazepam prior to succeeding studies on the oral disposition of the drug. A preparation for intravenous administration was created. Clearance was chosen as measurement of the capacity to glucuronidate oxazepam. Severe decompensated liver disease was associated with a significant decrease in oxazepam clearance, that became even more obvious when corrected for by a diminished binding to plasma proteins. This increase in free fraction of oxazepam was substantial and could mainly be accounted for by low plasma albumin values. The results are in part a settlement with earlier studies on glucuronidation in liver disease and they may undoubtedly be ascribed to the severe degree of liver disease. For the first time it was shown that hypothyroidism led to a decline in the clearance and metabolism of oxazepam and paracetamol that is mainly biotransformed by glucuronidation. It was concluded that the enzymes responsible for glucuronidation in hypothyroidism are under the influence of thyroid hormones as is the case with oxidative enzymes. Further studies focused on the effect of host and environmental factors on glucuronidation. A commercially available very low calorie product for the treatment of obesity resulted in a decrease in oxazepam clearance and a lack of co-factors as a consequence of the low calorie intake was explanatorily proposed. Beta-adrenoceptor antagonists are often prescribed together with other drugs and close knowledge on interactions is mandatory but insufficient in regard of drugs being glucuronidated. Despite the mutual metabolic pathway labetalol exerted no dispositional alterations concerning oxazepam. It was moreover suggested that very elderly subjects between the age of 80 to 94 years had a reduced clearance of oxazepam.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetaminophen-induced depletion of glutathione and cysteine in the aging mouse kidney

Glutathione (GSH) plays an essential role in the detoxification of acetaminophen (APAP) and the prevention of APAP-induced toxicity in the kidney. Our previous results demonstrated that a GSH deficiency is a general property of aging tissues, including the kidney, suggesting a hypothesis that senescent organisms are at greater risk to APAP-induced renal damage. To test this, C57BL/6NIA mice of different ages through the life span were injected with various doses of APAP, and the extent of GSH and cysteine (Cys) depletion and recovery were determined. At time intervals up to 24 hr, kidney cortex samples were obtained, processed and analyzed for glutathione status, namely GSH, glutathione disulfide (GSSG), Cys and cystine, using an HPLC method with dual electrochemical detection. In the uninjected controls, GSH and Cys concentrations decreased about 30% in the aging mouse, but the GSSG and cystine levels were unchanged during the life span. APAP administration depleted the kidney GSH and Cys contents in a dose- and time-dependent manner. Four hours after APAP administration, GSH levels of the young, growing (3- to 6-month) and the mature (12-month) mice decreased 34 and 58%, respectively, and recovered to near control values by 24 hr (95 and 98%). In contrast, the extent of depletion in old (31-month) mice was greater (64%) and the 24-hr recovery was less, returning only to 56%. Likewise, Cys levels of the young and mature mice decreased 49 and 65%, respectively, 4 hr following APAP, and increased to 99 and 85% by 24 hr. In contrast, in old mice, there was a 78% depletion after 4 hr followed by a recovery of only 65% by 24 hr. These results demonstrated clearly that in the aging mouse kidney, a GSH and Cys deficiency occurs that is accompanied by an impaired APAP detoxification capacity.

Glucuronidation of 3'-azido-3'-deoxythymidine in human liver microsomes: enzyme inhibition by drugs and steroid hormones

The molecular form of UDP-glucuronosyltransferase involved in the catalysis of 3'-azido-3'-deoxythymidine (AZT)-5'-O-glucuronide was characterized in human liver microsomes. The specific activity (1.3 nmol/min per mg protein) in transplantable liver was more than 2-times higher than in post-mortem fragments. Liver microsomes from patients suffering Crigler-Najjar syndrome, who are genetically deficient in bilirubin UDP-glucuronosyltransferase, could also glucuronidate AZT to a similar extent, thus indicating that this protein was not involved in that process. A genetically engineered V79 cell line stably expressing a cDNA which encodes a human isozyme active towards 1-naphthol was unable to glucuronidate AZT. Clinically used drugs, most of them being glucuronidated, were tested as potential inhibitors of the glucuronidation of AZT in human liver microsomes. The drugs chemically related to 2-phenylpropionic acid, naproxen and flurbiprofen, and the steroid compounds testosterone, estrone and ethynylestradiol strongly inhibited AZT glucuronidation. Codeine and morphine also decreased the reaction rate although to a lower extent. Except estrone which elicited a partial competitive inhibition, ethynylestradiol, flurbiprofen naproxen and testosterone could competitively inhibit AZT glucuronidation with an apparent Ki of 38, 50, 172 and 250 microM, respectively. The results suggest that these drugs were substrates of the same isozyme(s) involved in AZT glucuronidation. Probenecid was a weak inhibitor of the reaction (Ki 900 microM), only when non-disrupted microsomes were used. This drug may compete with the anion carrier system involved in the microsomal uptake of UDP-glucuronic acid.

Changes in conjugative enzyme activity and acetaminophen metabolism in young and senescent male F-344 rats following prolonged exposure to buthionine sulfoximine

This study examined how advanced age affects glucuronide and sulfate conjugation of acetaminophen after prolonged exposure to L-buthionine-S,R-sulfoximine (BSO) in male Fischer 344 rats. Young (4-5 month) and senescent (21-22 month) rats received 11 doses of BSO (2 mmol/kg) at 12-h intervals via a gastric cannula. Hepatic metabolism was assessed in vivo by measuring the products of reactions mainly responsible for acetaminophen elimination, namely the formation of the glucuronide and sulfate conjugates. Selected drug-metabolizing enzyme activities were also determined in vitro. BSO treatment increased the partial clearance to acetaminophen glucuronide by 90% and 41% in young and old rats, respectively, and similarly, induced p-nitrophenol and 1-naphthol UDP-glucuronosyl transferase activities to a greater extent in young versus senescent animals. Thus, the induction of these UDP-glucuronosyl transferase activities by BSO is preserved in senescent animals. Although the partial clearance to acetaminophen sulfate was decreased in senescent control rats compared to young controls, BSO treatment decreased the in vivo rate of sulfation in both age groups. Similar to previous findings with the Sprague-Dawley strain, BSO treatment did not induce hepatic cytochrome P-450 content or activity or cytosolic p-nitrophenol sulfotransferase activity in young and senescent Fischer 344 rats.

Drug glucuronidation in humans

Glucuronidation is a major metabolic pathway for a large number of drugs in humans. Conjugation of drugs and other chemicals with glucuronic acid is catalyzed by the multigene UDP-glucuronosyltransferase family. It is believed that a number (unspecified at present) of glucuronosyltransferase isozymes, which probably differ in terms of substrate specificity and regulation, contribute to drug glucuronidation. Factors known to influence the pharmacokinetics of glucuronidated drugs in man, presumably via an effect on specific glucuronosyltransferases, include age (especially the neonatal period), cigarette smoking, diet, certain disease states, coadministered drugs, ethnicity, genetics and hormonal effects.

Hepatic drug metabolism and aging

Although there is considerable variation in the effect of age on drug biotransformation, the metabolism of many drugs is impaired in the elderly. Age-related physiological changes, such as a reduction in liver mass, hepatic metabolising enzyme activity, liver blood flow and alterations in plasma drug binding may account for the decreased elimination of some metabolised drugs in the elderly. It is difficult, however, to separate an effect of aging from a background of marked variation in the rate of metabolism due to factors such as individual metabolic phenotype, environmental influences, concomitant disease states and drug intake. The prevailing data suggest that initial doses of metabolised drugs should be reduced in older patients and then modified according to the clinical response. In most studies the elderly appear as responsive as young individuals to the effects of compounds which induce or inhibit the activity of cytochrome P450 isozymes. Concurrent use of other agents, which induce or inhibit drug metabolism, mandates dose adjustment as in younger patients. Many questions remain unanswered. For instance, limitations of in vitro studies prevent any firm conclusion about changes in hepatic drug metabolising enzyme activity in the elderly. With aging, some pathways of drug metabolism may be selectively affected, but this has not been adequately scrutinised. The possibility that metabolism of stereoisomers may be altered in the elderly has not been adequately tested. The effect of aging on the distribution of polymorphic drug metabolism phenotypes is still not established, despite potential implications for disease susceptibility and survival advantage.