In vivo age-related changes in hepatic drug-oxidizing capacity in humans

Genetic polymorphism in cytochrome P450 2D6 (CYP2D6): Population distribution of CYP2D6 activity

Cytochrome P-450 2D6 (CYP2D6) is involved in the metabolism of many therapeutic drugs even though the enzyme represents a small proportion of the total CYP content of human liver. In vivo phenotyping with probe drug substrates such as debrisoquine and dextromethorphan showed a clear separation between poor metabolizers (PM) and extensive metabolizers (EM). This polymorphism may affect susceptibility to environmental disease, as suggested by molecular epidemiologic studies that found an association between CYP2D6 metabolizer phenotype and cancer risk; however, this association is not consistent. There are only a few examples of CYP2D6 involvement in toxicant mechanism of action, but this has not been extensively studied. Gene probe studies documented a number of genetic polymorphisms that underlie CYP2D6 metabolizer phenotypes. The EM group carries the wild-type (*1) or active (*2) variant alleles, while the PM group carries the *3, *4, *5, or *6 alleles, all of which code for a protein that has lower or null CYP2D6 activity. The current analysis characterizes (a) influence of genotype on phenotype based upon in vivo metabolism studies of probe drugs and (b) frequency of the major genotypes in different population groups is also characterized. These data were then incorporated into Monte Carlo modeling to simulate population distributions of CYP2D6 activity. This analysis reproduced the bimodal distributions commonly seen in phenotyping studies of Caucasians and found extensive population variability in enzyme activity, as indicated by the 9- to 56-fold difference between the PM modal median and the total population median CYP2D6 activity. This substantial degree of interindividual variability in CYP function indicates that assessments involving CYP2D6 substrates need to consider the full distribution of enzyme activity in refining estimates of internal dose in health assessments of xenobiotics.

Genetic polymorphism in CYP2E1: Population distribution of CYP2E1 activity

Cytochrome P-450 2E1 (CYP2E1) is a key enzyme in the metabolic activation of a variety of toxicants including nitrosamines, benzene, vinyl chloride, and halogenated solvents such as trichloroethylene. CYP2E1 is also one of the enzymes that metabolizes ethanol to acetaldehyde, and is induced by recent ethanol ingestion. There is evidence that interindividual variability in the expression and functional activity of this cytochrome (CYP) may be considerable. Genetic polymorphisms in CYP2E1 were identified and linked to altered susceptibility to hepatic cirrhosis induced by ethanol and esophageal and other cancers in some epidemiological studies. Therefore, it is important to evaluate how such polymorphisms affect CYP2E1 function and whether it is possible to construct a population distribution of CYP2E1 activity based upon the known effects of these polymorphisms and their frequency in the population. This analysis is part of the genetic polymorphism database project described in the lead article in this series and followed the approach described in that article (Ginsberg et al., 2009, this issue). Review of the literature found that there are a variety of CYP2E1 variant alleles but the functional significance of these variants is still unclear. Some, but not all, studies suggest that several upstream 5' flanking mutations affect gene expression and response to inducers such as ethanol or obesity. None of the coding-region variants consistently affects enzyme function. Part of the reason for conflicting evidence regarding genotype effect on phenotype may be due to the wide variety of exposures such as ethanol or dietary factors and physiological factors including body weight or diabetes that modulate CYP2E1 expression. In conclusion, evidence is too limited to support the development of a population distribution of CYP2E1 enzyme activity based upon genotypes. Health risk assessments may best rely upon data reporting interindividual variability in CYP2E1 function for input into physiologically based pharmacokinetic (PBPK) models involving CYP2E1 substrates.

Exact profiles of (13)CO(2) recovery in breath air after per oral administration of [(13)C]methacetin in two groups of different ages

The aim of this study is to determine if age is a factor influencing the results of a [(13)C]methacetin breath test ((13)C-MBT). Two groups of healthy volunteers, each comprising six men and six women, but differing in average age (Y=young, 25.1+/-0.6 years, MA=middle-aged;, 46.0+/-2.1 years) orally took 75 mg [(13)C]methacetin. Samples of expiratory air for (13)CO(2) measurement were collected up to 48 h after intake of the substrate. A maximum momentary (13)CO(2) breath exhalation of 37.0+/-2.6%dose/h was observed at 18 min (median, range: 9-30 min) in the young subjects and of 38.4+/-2.5%dose/h at 18 min (median, range: 12-30 min) in the middle-age volunteers. The cumulative (13)C elimination in expiratory air was statistically significantly higher in the MA compared with the Y group as from 75 min up to 180 min, indicating a greater microsomal metabolic efficiency of the liver in the middle-aged healthy subjects. Gender, use of hormonal contraception, cigarette smoking, or body mass index did not modify the age-related effect on the cumulative (13)C elimination in breath air. The study results imply a necessity of composing control groups well matched with regard to the age structure for a proper interpretation of clinical (13)C-MBT results.

Myocardial transcriptional profiles in a murine model of sepsis: evidence for the importance of age

BACKGROUND

Age influences outcome of sepsis and septic shock. The mechanism of this age-dependent vulnerability to sepsis remains largely unknown. Because much of the mortality and morbidity associated with sepsis and septic shock is the result of severe derangements in the cardiovascular system, it is possible that the myocardium responds to injury in a developmentally influenced manner. We hypothesized that analysis of cardiac RNA expression profiles may differentiate between the myocardial response to sepsis in young and old mice.

METHODS AND RESULTS

Sixteen FVB/N male mice were stratified based on age. Young animals were 6 wks old, correlating to 4 to 6 human years, and aged animals were 20 months old correlating to 70 to 80 human years. Animals underwent either cecal ligation and puncture to produce polymicrobial sepsis or a sham operation. Both ventricles were excised after kill at 24 hrs. There were 53 genes that differed in RNA abundance between the four groups (false discovery rate of 0.005, p < 0.00001). Additionally, four genes were associated with an age-dependent response to sepsis: CYP2B2 (cytochrome P450, family 2, subfamily B, polypeptide 6), VGLL2 (vestigial like 2), and PAH (phenylalanine hydroxylase). The fourth gene is an expressed sequence tag, the function of which is related to the cytochrome P450 family. These genes play roles in phenylalanine, tyrosine, tryptophan, and fatty acid metabolism.

CONCLUSIONS

This report describes the transcriptional response of the heart to sepsis. In addition, our findings suggest that these differences are in part age-dependent and serve as hypothesis generation.

Precision-cut liver slices from rats of different ages: basal cytochrome P450-dependent monooxygenase activities and inducibility

The biotransformation capacity - of the cytochrome P450 (CYP) system for example - is lower but inducibility is more pronounced in neonates than in adults. On the other hand, both enzyme activities and inducibility decline with senescence. Precision-cut rat liver slices are widely used as an in vitro tool for the examination of drug toxicity, xenobiotic metabolism or enzyme induction. The aim of the present study was to assess whether age-related changes in CYP activities and induction observed in vivo are also mirrored in vitro in liver slices. For this purpose, different CYP model reactions were measured in precision-cut liver slices from one-day-old, 40-day-old and one-year-old rats after in vitro exposure to various inducers. Similar to the in vivo situation, basal CYP activities were distinctly lower and inducibility was much more pronounced in liver slices from neonatal than in those from adult animals. Also, enzyme activities were mostly somewhat lower in liver slices from aged rats compared to those from 40-day-old rats. However, CYP inducibility was less pronounced than with younger animals too. Thus, precision-cut rat liver slices are a suitable in vitro tool for investigating age-related changes in CYP activities and induction as well as developmental differences in drug metabolism and toxicity.

Actual and potential drug interactions associated with methadone

OBJECTIVE

To identify and characterize methadone-related drug interactions, as well as factors accounting for the variability in manifesting these interactions clinically.

DESIGN

Systematic review of the primary literature.

METHODS

Over 200 articles, reports of clinical trials, and case reports were reviewed. Studies and case reports were included if they revealed either quantitative or qualitative methods to identify, evaluate severity of, or compare methadone-related drug interactions.

RESULTS OF DATA SYNTHESIS

The evidence base associated with methadone drug interactions is underdeveloped in general, as the majority of references found were case reports or case series. Most of the studies and reports focused on inpatients receiving methadone maintenance treatment (MMT) that were between 20 and 60 years of age, taking 200 mg/day of methadone or less. Evidence supporting the involvement of lesser known cytochrome P450 enzymes such as 2B6 is emerging, which may partially explain the inconsistencies previously found in studies looking specifically at 3A4 in vitro and in vivo. Genetic variability may play a role in the pharmacokinetics and pharmacodynamics of many medications, including methadone.

CONCLUSIONS

Drug interactions associated with methadone and their clinical significance are still poorly understood in general. Many tertiary drug information references and review articles report interactions associated with methadone in a general sense, much of which is theoretical and not verified by case reports, much less well-designed clinical trials. The majority of drug interaction reports that do exist were performed in the MMT population, which may differ significantly from chronic pain or cancer pain populations.

Antimuscarinics for the treatment of overactive bladder: a review of central nervous system effects

Antimuscarinic drugs commonly used to treat overactive bladder are often associated with central nervous system (CNS) side effects including cognitive dysfunction, memory impairment, dizziness, fatigue, and headache. New agents show reduced CNS penetrance and better selectivity for the M3 muscarinic receptor. However, changes associated with aging may lead to alterations in blood-brain barrier permeability. Therefore, use of antimuscarinics in the elderly or in patients with Alzheimer's disease presents a significant challenge. This review highlights muscarinic receptor distribution and function in the CNS, provides a description and incidence of CNS side effects with therapy, offers information specific to currently available agents, and describes the use of antimuscarinics in special populations including children, the elderly, and patients with Alzheimer's disease.

Pharmacokinetic-Pharmacodynamic Crisis in the Elderly

Advances in medical technology have led to improved survival after catastrophic illnesses. Many of the survivors require ongoing care including tracheostomy, mechanical ventilation, tube feedings, and indwelling venous catheters. Repeated hospitalizations may be necessary to treat infectious complications resulting from resistant organisms requiring intravenous antibiotic therapy. Because prolonged intravenous access may be difficult or even impossible in these patients, alternative means of therapy are necessary. Linezolid is the first of a new class of antimicrobial agents known as the oxazolidinones with activity against gram-positive bacteria similar to that of vancomycin and yet its oral bioavailability allows for enteral administration. We present our retrospective experience with oral linezolid in a cohort of pediatric intensive care unit patients. Primary infectious disease issues included endocarditis, tracheitis, pneumonia, or central line sepsis resulting from Staphylococcus epidermidis, methicillin-resistant Staphylococcus aureus, and Enterococcus. Treatment was initiated with vancomycin and changed to enteral linezolid (10 mg/kg every 12 hours). The duration of therapy with linezolid varied from 7 days to 6 weeks. All of the patients were discharged home to complete their course of enteral linezolid. No complications related to linezolid therapy were noted, and all of the patients completed their prescribed course of therapy without the need for rehospitalization. Our preliminary experience suggests that oral linezolid offers an effective alternative to intravenous vancomycin for the treatment of infections resulting from gram-positive bacteria and avoids the need for prolonged vascular access.

Warfarin metabolism and anticoagulant effect: a prospective, observational study of the impact of CYP2C9 genetic polymorphism in the presence of drug-disease and drug-drug interactions

BACKGROUND

Cytocbrome P450 (CYP) 2C9 polymorphism affects the warfarin dosage requirement in stable outpatients. However, it is not known whether the CYP2C9 genotype contributes to the variability in warfarin dosage in the presence of drug-disease and drug-drug interactions.

OBJECTIVE

The aim of this study was to examine the effects of CYP2C9 genetic polymorphism on warfarin dosage requirements in patients with severe comorbid conditions and those treated with medications that potentially interact with warfarin.

METHODS

This prospective, observational study was conducted at Hadassah University Hospital, Jerusalem, Israel. Data from consecutive patients treated with warfarin for at least 3 months and admitted to the internal medicine ward were eligible for inclusion. Clinical data, international normalized ratio (INR), and warfarin dosage were recorded from medical records. The CYP2C9 genotype was determined using polymerase chain reaction restriction fragment length polymorphism, and plasma concentrations of (S)- and (R)-warfarin were determined by high-performance liquid chromatography using chiral methods.

RESULTS

One hundred nineteen subjects (52% women) were studied. Mean age was 65.8 years (95% CI, 63.1-68.4), and weight was 74.9 kg (95% CI, 72.1-77.7). The mean warfarin dosage was 33% lower in patients with the CYP2C9-*1/*3 genotype (mean [SEM], 0.045 [0.006] mg/kg x d(-1)) compared with the CYP2C9-*1/*1 genotype (0.067 [0.004] mg/kg x d(-1)) (P=0.008); an intermediate value was found for the CYP2C9-*1/*2 genotype (0.062 [0.008] mg/kg x d(-1)). However, despite the lower dosage, INR was significantly higher in patients with the *1/*3 genotype (mean [95% CI], 3.29 [2.44-4.14]) (n=18) compared with the *1/*1 genotype (2.52 [2.34-2.71]) (n=64) (P=0.029). In addition to genotype, older age, congestive heart failure (CHF), and treatment with antibiotics were associated with lower warfarin dosages, whereas treatment with drug-metabolism inducers was associated with higher warfarin dosages. In addition, the ratios of (S)- to (R)-warfarin concentrations were significantly higher in patients with *1/*3 compared with those in patients with the *1/*1 genotype.

CONCLUSIONS

In this study population of patients with severe comorbid conditions and those treated with medications that potentially interact with warfarin, CYP2C9 *1/*3 genotype, older age, CHF, and the use of antibiotics were associated with lower warfarin dosage requirements. The CYP2C9*1/*3 genotype, compared with CYP2C9 *1/*1, was associated with 33% lower mean warfarin dosage requirements and higher INR values, which were higher than the upper therapeutic range of INR (ie, 3). Genetic CYP2C9 polymorphism contributed to the variability in warfarin dosage requirements in the presence of drug-disease and drug-drug interactions.

The Effect of Acetaminophen on the International Normalized Ratio in Patients Stabilized on Warfarin Therapy

STUDY OBJECTIVE

To determine whether an interaction exists between acetaminophen and warfarin that alters the international normalized ratio (INR).

DESIGN

Prospective, randomized, double-blind, placebo-controlled trial.

SETTING

Anticoagulation clinic at a Veterans Affairs Medical Center.

PATIENTS

Thirty-six adult patients receiving warfarin with stable INRs, defined as two consecutive INRs at least 3 weeks apart that were within the therapeutic range.

INTERVENTION

Patients were randomly assigned to receive acetaminophen 1 g twice/day along with matching placebo twice/day (12 patients), acetaminophen 1 g 4 times/day (12 patients), or matching placebo 4 times/day (12 patients) for 4 weeks.

MEASUREMENTS AND MAIN RESULTS

The primary end point was the difference in mean INR between groups at weekly intervals. Secondary end points were the percentages of patients in each group with supratherapeutic (INR > or = 0.3 above the upper limit of their therapeutic range) or subtherapeutic (INR > or = 0.2 or 0.3 below the lower limit of their respective therapeutic range of 2.0-3.0 or 2.5-3.5) INRs, and the difference in mean serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels between groups at biweekly intervals. Slow enrollment and a preliminary observation that 15 patients experienced an elevated INR prompted early termination of the study. At week 2, the group receiving acetaminophen 2 g/day had a significantly higher mean INR versus the placebo group (p=0.01). At weeks 1, 2, and 3, the acetaminophen 4-g/day group had significantly higher mean INRs compared with those in the placebo group (p=0.04, p=0.01, p=0.01, respectively). In addition, 13 (54%) of 24 patients in the acetaminophen groups combined exceeded the upper limit of their therapeutic range by 0.3 or greater compared with only 2 (17%) of 12 patients in the placebo group. No statistically significant differences in serum ALT or AST levels between either acetaminophen group versus the placebo group were found at week 4; however, there was a statistically significant increase in mean ALT level at week 2 in the acetaminophen 4-g/day group versus the placebo group.

CONCLUSION

These findings support the existence of a clinically significant interaction between warfarin and daily use of acetaminophen 2-4 g, necessitating close monitoring of patients who receive this drug combination. Whether this interaction occurs when acetaminophen is taken in lower doses or is used sporadically requires further study.

[Ibuprofen in childhood: evidence-based review of efficacy and safety]

Ibuprofen is the non-steroidal anti-inflammatory drug most prescribed for the treatment of fever and moderate pain in childhood. Its analgesic and antipyretic efficacy is now well documented: at equal doses ibuprofen appears slightly more effective than acetaminophen in the treatment of fever and is equivalent for analgesia. However, adverse effects should be taken into account in the choice between ibuprofen and acetaminophen. Lot of studies (case reports, cohort studies, case-control studies and one multicenter double-blind randomized control trial) have reported ibuprofen adverse effects at therapeutics doses. These data suggest there is an increased risk of invasive group A streptococcal infection after chickenpox and of acute renal failure in case of hypovolemia after a treatment by ibuprofen. Gastroduodenal and hemorrhagic adverse events could also happen, but the causality with ibuprofen is not demonstrated. Therefore, ibuprofen is not recommended for the treatment of fever or moderate pain during chickenpox or during a disease with a risk of dehydration, until other pharmacoepidemiology studies more accurately quantify the risk of adverse events of ibuprofen in children.

Evaluation of urinary trans-3'-hydroxycotinine as a biomarker of children's environmental tobacco smoke exposure

The utility of urinary trans-3'-hydroxy cotinine (3HC) as a biomarker of environmental tobacco smoke (ETS) exposure was investigated in comparison with urinary cotinine (COT), the sum (3HC + COT), and ratio of the two nicotine metabolites (3HC/COT). Participants were 150 ETS exposed children (aged 1-44 months) and their parents. Child urine samples were collected during 3weekly baseline assessments and at interviews administered 3, 6, 12, and 18 months after baseline. Findings indicate that 3HC and COT can be measured reliably (rho = 0.96, 0.88) and show equivalent levels of repeated measures stability (rho = 0.71, 0.75). COT, 3HC, and 3HC + COT showed equally strong associations with air nicotine levels, reported ETS contamination, and reported ETS exposure (r=0.60-0.70). The intraclass correlations of 3HC/COT were lower than those for COT or 3HC. Older children had a higher 3HC/COT ratio than younger children (3.5 versus 2.2), and non-Hispanic White children had a higher ratio than African-American children (3.2 versus 1.9). These findings suggest that COT, 3HC, and 3HC + COT are approximately equivalent and equally strong biomarkers of ETS exposure in children. Moreover, 3HC/COT may provide a useful indicator to investigate age- and race-related differences in the metabolism of COT and 3HC.

Effect of conjugated equine estrogens on oxidative metabolism in middle-aged and elderly postmenopausal women

The effects of conjugated equine estrogens (CEE) 0.625 mg daily on cytochrome P450 (CYP) were quantified in 12 middle-aged and 13 elderly postmenopausal women at baseline and 6 months later. CYP phenotype was characterized by caffeine (CYP1A2), chlorzoxazone (CYP2E1), dapsone (CYP, N-acetyltransferase 2), dextromethorphan (CYP2D6), and mephenytoin (CYP2C19) metabolism. CEE significantly decreased CYP1A2 (caffeine metabolic ratio: 0.57 +/- 0.20 before, 0.40 +/- 0.20 after, P = .001) and significantly increased CYP2D6 (dextromethorphan/dextrorphan ratio: 0.0116 +/- 0.0143 before, 0.0084 +/- 0.0135 after, P = .022) metabolism. CEE had no overall effect on CYP2C19, CYP2E1, CYP-mediated dapsone metabolism, and N-acetyltransferase 2. The dextromethorphan metabolic ratio decreased only in the seniors. The dapsone recovery ratio decreased in the middle-aged group and increased in the seniors. CEE significantly influenced CYP1A2, CYP2D6, and CYP-mediated dapsone oxidative metabolism but not CYP2C19, CYP2E1, or N-acetyltransferase 2 metabolism in postmenopausal women. Age influenced CYP2D6 metabolism and dapsone hydroxylation.

Age‐Related Changes in Pharmacokinetics: Predictability and Assessment Methods

Although there have been relatively few studies of the pharmacokinetics of antiepileptic drugs (AEDs) in old age, available evidence indicates that the clearance of most old and new generation AEDs is reduced on average by about 20-40% in elderly patients compared with nonelderly adults. Depending on the pharmacokinetic characteristics of the drug, the reduction in clearance can be ascribed to a physiological reduction in rate of drug metabolism, to a decrease in renal excretion rate, or to both. Studies have consistently demonstrated that interindividual pharmacokinetic variability in old age is particularly prominent, due not only to the influence of aging-related physiological changes, but also to the impact of comorbidities and drug-drug interactions. For extensively metabolized drugs, there are no reliable tools to predict with a high degree of accuracy the pharmacokinetic behavior of an AED in an individual patient. With renally eliminated drugs, determination of creatinine clearance may provide a useful clue in predicting individual changes in drug clearance and the consequent need for dosage adjustment. In the therapeutic setting, measurement of serum AED concentrations can be valuable in individualizing dosage in an elderly person, even though it should be remembered that in the case of drugs that are highly bound to plasma proteins the total serum concentration may underestimate the level of unbound, pharmacologically active drug. Because aging is also associated with important pharmacodynamic changes that may alter the relationship between serum drug concentration and pharmacological effects, pharmacokinetic measurements alone are not a substitute for the need to monitor clinical response carefully and to adjust dosage accordingly.

Pharmacokinetics and toxicity of weekly docetaxel in older patients

PURPOSE

To evaluate the pharmacokinetics of weekly docetaxel in a cohort of older patients with metastatic cancer and to explore the relationship of pharmacokinetic variables, Erythromycin Breath Test results, age, geriatric assessment variables, and toxicity to therapy.

EXPERIMENTAL DESIGN

Twenty patients ages > or = 65 years with metastatic breast, prostate, or lung cancer entered an Institutional Review Board-approved protocol to evaluate the pharmacokinetics of weekly docetaxel administered at 35 mg/m2 i.v. for 3 weeks followed by a 1-week break. The Erythromycin Breath Test and geriatric assessment were done before the first dose. Blood samples were collected for pharmacokinetic analysis with the first dose of docetaxel.

RESULTS

Of the 20 patients who entered the study, 19 were evaluable. There were no age-related differences in the pharmacokinetics of weekly docetaxel. Fifty-eight percent (11 of 19) experienced grade > or = 3 toxicity: 16% (3 of 19) grade > or = 3 hematologic toxicity, and 53% (10 of 19) grade > or = 3 nonhematologic toxicity. There was an association between the Erythromycin Breath Test results and docetaxel pharmacokinetic variables; however, there was no association between Erythromycin Breath Test results or docetaxel pharmacokinetics with frequency of grade > or = 3 toxicity.

CONCLUSIONS

Despite no statistically significant age-related differences in weekly docetaxel pharmacokinetics, over half of these older patients experienced a grade > or = 3 toxicity at the 35 mg/m2 starting dose. We advocate a starting dose of 26 mg/m2 on this weekly schedule and dose escalating if no toxicity.

Value of therapeutic drug monitoring of MMF therapy in pediatric transplantation

Therapeutic drug monitoring (TDM) is desirable whenever the desired drug effect cannot be predicted from a given dose, or when it is necessary to find a balance between the efficacy and toxicity of the drug. Children and adolescents particularly benefit from TDM, because dosing requirements are often not studied in the same detail as in adults. Also, drug-drug interactions are frequent. The gold standard for assessment of drug exposure is the area-under-the-curve (AUC) for a full pharmacokinetic profile. TDM for mycophenolic acid (MPA) is less well established. Monitoring of trough levels does not suffice because of enterohepatic recirculation of MPA after formation of its main metabolite, a glucoronide termed MPA-G. However, abbreviated sampling schemes specific to mycophenolate mofetil (MMF) correlate well with the AUC for MPA. Cyclosporine interacts with MPA by inhibiting the multidrug resistance-associated protein 2 (MRP2). Higher MPA concentrations result in a decreased two h concentration of cyclosporine, while higher cyclosporine exposure results in a lower MPA exposure. There are no drug interactions between tacrolimus and MPA, and lower doses of MMF are required in combination with tacrolimus. Steroids may induce the clearance of MPA, which could account in part for the increasing MPA exposure following transplantation. TDM has allowed for dosing recommendations of MMF in children, which could lead to improved efficacy and minimization of toxicities. It is important that these provisional target levels are validated in prospective studies. The above points clearly indicate that there is a role for TDM of MPA in pediatric transplant recipients.

Clinical assessment of effects of botanical supplementation on cytochrome P450 phenotypes in the elderly: St John's wort, garlic oil, Panax ginseng and Ginkgo biloba

OBJECTIVES

Elderly patients are more likely to ingest prescription medications concurrently with botanical supplements, and may therefore be vulnerable to herb-drug interactions. Phytochemical-mediated modulation of cytochrome P450 (CYP) activity may underlie many herb-drug interactions. Some evidence suggests that CYP activity may decrease in the elderly. If so, herb-mediated changes in CYP activity may take on greater clinical relevance in this population. In this study, single timepoint, phenotypic metabolic ratios were used to determine whether long-term supplementation of St John's wort, garlic oil, Panax ginseng, and Ginkgo biloba affected CYP1A2, CYP2D6, CYP2E1 or CYP3A4 activity in elderly subjects.

METHODS

Twelve healthy volunteers between the ages of 60 and 76 years (mean age 67 years) were randomly assigned to receive each botanical supplement for 28 days followed by a 30-day washout period. Probe drug cocktails of midazolam, caffeine, chlorzoxazone and debrisoquine were administered before and at the end of supplementation. Pre- and post-supplementation phenotypic ratios were determined for CYP3A4, CYP1A2, CYP2E1 and CYP2D6 using 1-hydroxymidazolam/midazolam serum ratios (1-hour), paraxanthine/caffeine serum ratios (6-hour), 6-hydroxychlorzoxazone/chlorzoxazone serum ratios (2-hour) and debrisoquine urinary recovery ratios (8-hour), respectively. The content of purported 'active' phytochemicals was determined for each supplement.

RESULTS

Comparisons of pre- and post-St John's wort phenotypic ratios revealed significant induction of CYP3A4 (approximately 140%) and CYP2E1 activity (approximately 28%). Garlic oil inhibited CYP2E1 activity by approximately 22%. P. ginseng inhibition of CYP2D6 was statistically significant, but the magnitude of the effect (approximately 7%) did not appear to be clinically relevant. None of the supplements tested in this study appeared to affect CYP1A2 activity.

CONCLUSIONS

Elderly subjects, like their younger counterparts, are susceptible to herb-mediated changes in CYP activity, especially those involving St John's wort. Pharmacokinetic herb-drug interactions stemming from alterations in CYP activity may adversely affect drug efficacy and/or toxicity. When compared with earlier studies that employed young subjects, the data suggest that some age-related changes in CYP responsivity to botanical supplementation may exist. Concomitant ingestion of botanical supplements with prescription medications, therefore, should be strongly discouraged in the elderly.

Active Drug Transport of Immunosuppressants

Immunosuppressants have a narrow therapeutic index, and pharmacokinetic variability negatively affects long-term outcome of transplantation. Recently, it has become clear that active transport is a major determinant of the inter-and intraindividual variability of the pharmacokinetics and pharmacodynamics of immunosuppressants. Active transport plays a key role in (1) the poor correlation between oral doses and systemic exposure of cyclosporine, tacrolimus, sirolimus, and everolimus, (2) tissue distribution including distribution into lymphocytes, (3) hepatic and intestinal metabolism, (4) the pharmacokinetic variability of immunosuppressants after oral dosing, (5) drug-drug interactions, (6) disease-drug interactions, and (7) age, gender, and ethnicity-based differences in pharmacokinetics of immunosuppressants. Those new insights may significantly improve patient management and long-term outcome not only by reducing pharmacokinetic variability and avoidance of drug-drug interactions but also by identification of sensitive patient populations. They will also significantly impact preclinical and clinical development strategies of new immunosuppressants.

Predicting and preventing adverse drug reactions in the very old

The size of the elderly population has been increasing steadily for several years. Individuals in this age group often have several concomitant diseases that require treatment with multiple medications. These drugs, for various reasons and especially as a consequence of potential accumulation, may be associated with adverse reactions. Of the numerous factors that can favour the occurrence of these adverse drug reactions, the most important are the pathophysiological consequences of aging, particularly as these apply to the very old. Although absorption of drugs is not usually reduced in the elderly, diffusion, distribution and particularly elimination decline with age. Furthermore, while hepatic metabolic function is fairly normal, renal function is usually markedly depressed in very old individuals, and this can translate into clinical consequences if it is not taken into account. This is why, before administration of any drug in the elderly, evaluation of glomerular filtration rate is essential. Validated estimations such as those obtained from the classical Cockcroft-Gault formula or from more recent methodologies are required. In addition to reductions in various organ functions, factors connected with very old age such as frailty, falls, abnormal sensitivity to medications and polypathology, all of which tend to be more common in the last years of life, all directly impact on adverse drug reaction occurrence. Given these characteristics of the elderly population, the best way to reduce the prevalence of adverse drug reactions in this group is to limit drug prescription to essential medications, make sure that use of prescribed agents is clearly explained to the patient, give drugs for as short a period as possible, and periodically re-evaluate all use of drugs in the elderly.

Prospective evaluation of the pharmacokinetics and toxicity profile of docetaxel in the elderly

PURPOSE

To prospectively study the pharmacokinetics and toxicity profile of docetaxel in elderly patients with cancer.

PATIENTS AND METHODS

Docetaxel was administered at a dose 75 mg/m(2) once every 3 weeks to 25 elderly cancer patients aged >/= 65 years and 26 cancer patients aged younger than 65 years. Pharmacokinetic studies and toxicity assessments were performed during the first cycle of therapy.

RESULTS

Of 51 patients treated, 20 aged >/= 65 years (median, 71 years; range, 65 to 80 years) and 20 aged younger than 65 years (median, 53 years; range, 26 to 64 years) were assessable for pharmacokinetic studies, and 39 were assessable for toxicity. Patient characteristics were similar (P >/= .15) between the two cohorts. Mean docetaxel clearance was not altered in the elderly versus younger patients: 30.1 L/h (standard deviation [SD] 18.3 L/h) v 30.0 L/h (SD, 14.8 L/h; P = .98). The percentage of patients with grade 4 and febrile neutropenia was higher in the elderly (63% and 16%, respectively) versus younger (30% and 0%, respectively) cohort, although this observation did not reach a level of statistical significance (P = .056). From logistic regression analysis, the odds ratio for a patient aged 65 years was 1.98 for developing grade 4 neutropenia compared with a patient aged 50 years (P = .091).

CONCLUSION

Docetaxel plasma pharmacokinetics are unaltered in elderly patients. Patients aged >/= 65 years appear to be more sensitive to docetaxel-induced neutropenia.

Soybean Oil Fat Emulsion Prevents Cytochrome P450 mRNA Down-Regulation Induced by Fat-Free Overdose Total Parenteral Nutrition in Infant Rats

Changes in the mRNA expression of hepatic cytochrome P450 (CYP) isoenzymes associated with overdose of fat-free or fat-containing total parenteral nutrition (TPN) were investigated in infant rats. Three-week-old male Sprague-Dawley rats were divided into three groups: group 1 received an oral diet, group 2 received TPN without fat, and group 3 received TPN with 20% of calories from fat (soybean oil emulsion). After TPN administration for 4 d, serum aspartate aminotransferase (AST) levels in group 2 were significantly increased (p<0.01) compared with the other groups. The mRNA expression of hepatic CYP isoenzymes in group 2 decreased to 0.76 to 31% of that in group 1 (p<0.01), but that in group 3 was maintained at 32 to 84% of that in group 1. These results indicate the importance of including fat in TPN regimens to prevent not only hepatic dysfunction but also mRNA down-regulation of liver CYP isoenzymes.

Factors Affecting Cytochrome P-450 3A Activity in Cancer Patients

PURPOSE

The purpose is to identify the demographic, physiologic, and inheritable factors that influence CYP3A activity in cancer patients.

EXPERIMENTAL DESIGN

A total of 134 patients (62 females; age range, 26 to 83 years) underwent the erythromycin breath test as a phenotyping probe of CYP3A. Genomic DNA was screened for six variants of suspected functional relevance in CYP3A4 (CYP3A4*1B, CYP3A4*6, CYP3A4*17, and CYP3A4*18) and CYP3A5 (CYP3A5*3C and CYP3A5*6).

RESULTS

CYP3A activity (AUC(0-40 min)) varied up to 14-fold in this population. No variants in the CYP3A4 and CYP3A5 genes were a significant predictor of CYP3A activity (P > 0.2954). CYP3A activity was reduced by approximately 50% in patients with concurrent elevations in liver transaminases and alkaline phosphatase or elevated total bilirubin (P < 0.001). In a multivariate analysis, CYP3A activity was not significantly influenced by age, sex, and body size measures (P > 0.05), but liver function combined with the concentration of the acute-phase reactant, alpha-1 acid glycoprotein, explained approximately 18% of overall variation in CYP3A activity (P < 0.001).

CONCLUSIONS

These data suggest that baseline demographic, physiologic, and chosen genetic polymorphisms have a minor impact on phenotypic CYP3A activity in patients with cancer. Consideration of additional factors, including the inflammation marker C-reactive protein, as well as concomitant use of other drugs, food constituents, and complementary and alternative medicine with inhibitory and inducible effects on CYP3A, is needed to reduce variation in CYP3A and treatment outcome to anticancer therapy.

Time-related clinical determinants of long-term tacrolimus pharmacokinetics in combination therapy with mycophenolic acid and corticosteroids: a prospective study in one hundred de novo renal transplant recipients

BACKGROUND

Tacrolimus is an efficient primary immunosuppressive drug in renal transplantation but its long-term use is associated with calcineurin-inhibitor-related toxicity. The specific characteristics of the inter-relationship between dose, concentration and clinical (side-)effects for tacrolimus have not yet been identified and extensive long-term pharmacokinetic studies are presently lacking.

OBJECTIVE

To establish the characteristics of the long-term pharmacokinetics of tacrolimus, to determine the time-dependent factors that influence the pharmacokinetics within the first critical post-transplant year and to identify a more appropriate way of monitoring drug exposure in clinical practice.

STUDY DESIGN

A prospective pharmacokinetic study of tacrolimus was conducted in 100 de novo renal allograft recipients during the first year post-transplantation.

METHODS

Area under the concentration-time curve (AUC) blood samplings for tacrolimus were performed on days 7, 42, 90, 180 and 360 for all patients. Model-independent pharmacokinetic parameters for tacrolimus were calculated and dose-corrected when appropriate: AUC12, peak plasma concentration (Cmax), pre-dose trough concentration (C0), time to Cmax, average steady-state blood concentration, steady-state total body clearance, terminal half-life, volume of distribution and an estimate for tacrolimus bioavailability was derived from additional steady-state intravenous clearance data. The association between tacrolimus pharmacokinetic parameters and different clinical variables was evaluated on days 7, 42, 90, 180 and 360. The clinical variables were either donor-related (e.g. donor age), transplantation-related (e.g. delayed graft function), recipient-related (e.g. bodyweight), biochemical (e.g. serum albumin), therapeutic variables (e.g. corticosteroid dose) or disease variables (e.g. liver dysfunction).

RESULTS

Long-term tacrolimus dose-corrected exposure (AUC12, C0) is characterised by a late significant increase towards the end of the first year post-transplantation as the result of a significant increase in tacrolimus bioavailability (p < 0.05) and a slow decrease in tacrolimus steady-state clearance. Consequently, tacrolimus dose-requirements corrected for bodyweight decrease significantly in the first postoperative year (p < 0.05), in part because of the simultaneous tapering of the corticosteroid dose which significantly affects tacrolimus bioavailability (p < 0.05). Other clinical variables that significantly influenced tacrolimus administration, exposure and bioavailability in a time-related fashion were identified in this study (renal allograft function [p < 0.05], liver dysfunction [p < 0.05], diarrhoea [p < 0.05]), while the clinical relevance of other variables was considerably moderated by our findings (serum albumin, haematocrit). Time-unrelated variables proved to be of significant continuing clinical importance for tacrolimus dose-exposure pharmacokinetics throughout the first post-transplant year (recipient age [p < 0.05], gender [p < 0.01] and donor-receptor gender mismatch [p < 0.05]), while donor hypotension (p < 0.05) and cold ischaemia time (p < 0.05) also proved significant although at present the reasons for this are unknown. Finally, using multiple stepwise regression analysis we demonstrated that classical assessment of tacrolimus exposure by monitoring pre-dose trough blood concentration (or any other single concentration sampling timepoint) is not the most reliable method and that abbreviated AUC measurements may constitute a more accurate clinical tool for (therapeutic) monitoring of drug exposure.

CONCLUSION

Tacrolimus pharmacokinetics in the first year after renal transplantation are characterised by a specific time-dependent evolution. The identification of clinical variables that determine tacrolimus pharmacokinetics is an important aid in the development of reliable drug monitoring strategies using abbreviated AUC measurements.

Does paracetamol potentiate the effects of oral anticoagulants?: a literature review

Paracetamol (acetaminophen) is the analgesic and antipyretic therapy of choice for patients receiving oral anticoagulation. It is widely used by patients in both prescription and over-the-counter products, resulting in frequent co-prescription with oral anticoagulants, especially in elderly patients. Indeed, older patients are the most likely to receive this combination of drugs because indications for both oral anticoagulation and analgesic therapy increase with age. For many years reports have presented evidence both for and against the idea that paracetamol may potentiate the anticoagulant effect of oral anticoagulants, thus increasing haemorrhagic risk in patients receiving this combination of drugs. This issue has continued to be a matter of debate in recent publications. No clear practical conclusion can be drawn from the studies because of methodological bias and the lack of clinical relevance. No prospective, randomised study assessing the effect of paracetamol on the anticoagulant effect of oral anticoagulants as used in clinical practice (i.e. the types of patients and dosages used in clinical practice) are available in the literature. The implications are considerable since on the one hand, the ingestion of paracetamol may be a cause of altered anticoagulation in patients who regularly take oral anticoagulation and who may have a haemorrhagic risk factor; and on the other hand, paracetamol might be the analgesic drug of choice that can be used without the need for any restrictions in patients receiving oral anticoagulant drugs. A comprehensive search of Medline and EMBASE for studies and case reports from 1966-2002 was performed in order to review the available literature on the interaction between paracetamol and oral anticoagulant drugs. In conclusion, the potential interaction between oral anticoagulant drugs and paracetamol is an important unanswered question, due to the growing incidence of the concomitant use of these drugs and the possible bleeding implications. The association between paracetamol and the occurrence of excessive INR values remains controversial due to lack of prospective clinical studies assessing the effect of the prescription of paracetamol in patients receiving long-term oral anticoagulation in clinical conditions. Such a study is currently ongoing.

Use of Beta-Blockers in Older Adults with Chronic Heart Failure

Most heart failure patients are older adults. Angiotensin-converting enzyme (ACE) inhibitors reduce mortality and morbidity in patients with systolic heart failure. However, the annual mortality rate in patients with systolic heart failure receiving ACE inhibitors is about 12%. Beta-blockers further reduce mortality rate by an additional 35% to 65%. Because of potential adverse effects, the rate of beta-blocker use is likely to be low in older adults with systolic heart failure. In this article, we review the findings of the major beta-blocker trials in systolic heart failure and discuss the potential benefits and adverse effects of beta-blockers, along with various practical aspects of their use in older adults with systolic heart failure. Subgroup analyses of these trials suggest that the survival benefits of beta-blockers observed in the main trials are also observed in persons 65 years of age and older. However, data are limited for heart failure patients 85 years of age and older. About half of the older adults with heart failure do not have systolic heart failure, and currently there is no evidence that beta-blockers also improve survival in these patients. Beta-blockers might play a beneficial role in heart failure patients without systolic heart failure by reducing high blood pressure, high heart rate, or myocardial ischemia, conditions known to impair ventricular relaxation. Adequate knowledge of the commonly used beta-blockers, along with careful patient selection and close monitoring for adverse effects will allow safe initiation and continuation of beta-blocker use for older adults with systolic heart failure. It is likely that lower doses of beta-blockers are as effective as higher doses.

Alosetron repeat dose pharmacokinetics, effects on enzyme activities, and influence of demographic factors

AIM

To assess the pharmacokinetics of alosetron, its effect on in vivo enzyme activities, and influence of demographic factors during repeated dosing.

METHODS

Thirty healthy men and women received 1 mg oral alosetron twice-daily for 29.5 days and a single oral dose of a metabolic probe cocktail before and on the last day of alosetron dosing. Serum alosetron concentrations were measured on days 1, 8, 15, 22 and 29. Probe-substrate and metabolite concentrations were measured after each cocktail dose.

RESULTS

Alosetron accumulation in serum was negligible. Exposure to alosetron did not alter probe-metabolite/substrate ratios associated with CYP2C19, 2E1, 2C9, or 3A4 activity, but modestly decreased those associated with CYP1A2 and N-acetyltransferase activity. Systemic exposure to alosetron was higher in women, positively correlated with age and body mass index, and negatively correlated with CYP1A2 activity. Incidence of constipation was higher in women, but not associated with alosetron concentration.

CONCLUSIONS

Single dose data can reliably predict the pharmacokinetics of alosetron after repeated doses. Alosetron exhibits limited potential for inhibition of cytochrome P450-mediated metabolism. Interindividual differences in alosetron pharmacokinetics associated with demographic factors may be related to strong dependence on metabolism by CYP1A2.

Aging biology and geriatric clinical pharmacology

Population aging evokes doomsday economic and sociological prognostication, despite a minority of older people suffering significant dependency and the potential for advances in therapeutics of age-related disease and primary aging. Biological aging processes are linked mechanistically to altered drug handling, altered physiological reserve, and pharmacodynamic responses. Parenteral loading doses need only be adjusted for body weight as volumes of distribution are little changed, whereas oral loading doses in some cases may require reduction to account for age-related increases in bioavailability. Age-related reduction of hepatic blood flow and hepatocyte mass and primary aging changes in hepatic sinusoidal endothelium with effects on drug transfer and oxygen delivery reduce hepatic drug clearance. Primary renal aging is evident, although renal clearance reduction in older people is predominantly disease-related and is poorly estimated by standard methods. The geriatric dosing axiom, "start low and go slow" is based on pharmacokinetic considerations and concern for adverse drug reactions, not from clinical trial data. In the absence of generalizable dosage guidelines, individualization via effect titration is required. Altered pharmacodynamics are well documented in the cardiovascular system, with changes in the autonomic system, autacoid receptors, drug receptors, and endothelial function to modify baseline cardiovascular tone and responses to stimuli such as postural change and feeding. Adverse drug reactions and polypharmacy represent major linkages to avoidable morbidity and mortality. This, combined with a deficient therapeutic evidence base, suggests that extrapolation of risk-benefit ratios from younger adults to geriatric populations is not necessarily valid. Even so, therapeutic advances generally may convert healthy longevity from an asset of fortunate individuals into a general social benefit.

Influence of aging on serum phenytoin concentrations: a pharmacokinetic analysis based on therapeutic drug monitoring data

The influence of aging on the pharmacokinetics of phenytoin at steady-state was evaluated retrospectically by comparing apparent oral clearance values (CL/F) in 75 patients aged 65-90 years (mean, 71.7 +/- 5.3 years) receiving phenytoin alone (n = 58) or in combination with phenobarbital (n = 17) and in an equal number of control patients aged 20-50 years (mean, 36.7 +/- 8.5 years) matched for gender, body weight, and comedication. All data were derived from the database of the therapeutic drug monitoring service (TDMS) of an academic neurological hospital. On average, elderly patients were found to exhibit slightly higher CL/F values compared with controls (14.6 +/- 4.7 ml h(-1) kg(-1) versus 13.1 +/- 4.2 ml h(-1) kg(-1), P < 0.05), the difference being probably related to the dose-dependent nature of phenytoin metabolism and the fact that elderly patients received lower dosages (4.4 +/- 1.1 mg kg(-1)day(-1) versus 5.3 +/- 1.1 mg kg(-1) day(-1), P < 0.001) and had lower serum phenytoin concentrations (14.1 +/- 5.7 microg ml(-1) versus 18.6 +/- 6.8 microg ml(-1), P < 0.0001). Gender and phenobarbital comedication were not found to exert any statistically significant influence on phenytoin CL/F. By contrast, in the elderly group, CL/F values were negatively correlated with age. On average, CL/F values decreased by about one-third between 65 and 85 years of age, but interindividual variability was considerable and age explained only 7.8% of the variation in CL/F in the elderly group. Overall, these findings indicate that aging is associated with a progressive decline in phenytoin clearance, presumably as a result of decreased drug metabolizing capacity. Because assessment was based on total serum phenytoin concentrations and the unbound fraction of phenytoin is known to decrease in old age, the influence of aging as quantified in this study may underestimate the magnitude of changes in the clearance of unbound, pharmacologically active drug. Based on these data, it is prudent to utilize initially smaller phenytoin dosages in old patients, and to make subsequent dose adjustments based on clinical response and serum drug level measurements. Interpretation of the latter, however, should take into account the possibility of an increase in the fraction of unbound drug.

Incorporating children's toxicokinetics into a risk framework

Children's responses to environmental toxicants will be affected by the way in which their systems absorb, distribute, metabolize, and excrete chemicals. These toxicokinetic factors vary during development, from in utero where maternal and placental processes play a large role, to the neonate in which emerging metabolism and clearance pathways are key determinants. Toxicokinetic differences between neonates and adults lead to the potential for internal dosimetry differences and increased or decreased risk, depending on the mechanisms for toxicity and clearance of a given chemical. This article raises a number of questions that need to be addressed when conducting a toxicokinetic analysis of in utero or childhood exposures. These questions are organized into a proposed framework for conducting the assessment that involves problem formulation (identification of early life stage toxicokinetic factors and chemical-specific factors that may raise questions/concerns for children); data analysis (development of analytic approach, construction of child/adult or child/animal dosimetry comparisons); and risk characterization (evaluation of how children's toxicokinetic analysis can be used to decrease uncertainties in the risk assessment). The proposed approach provides a range of analytical options, from qualitative to quantitative, for assessing children's dosimetry. Further, it provides background information on a variety of toxicokinetic factors that can vary as a function of developmental stage. For example, the ontology of metabolizing systems is described via reference to pediatric studies involving therapeutic drugs and evidence from in vitro enzyme studies. This type of resource information is intended to help the assessor begin to address the issues raised in this paper.

Postnatal development of hepatic oxidative, hydrolytic and conjugative drug-metabolizing enzymes in female horses

Little is known about the effects of aging on the hepatic drug metabolizing capacity of horses despite the relatively long lifespan characterizing this species. A wide array of cytochrome P450 (CYP)-dependent monooxygenases, carboxylesterases and transferases were assayed in liver microsomes from 50 female horses in an age range between less than 1 year to over 12 years. Rather unexpectedly, both the CYP content and the activity of NADPH cytochrome c reductase rose as a function of age. Accordingly, a general increasing trend was recorded in the rate of the in vitro metabolism of the substrates reported to be related to CYP2B-, CYP2E- or CYP3A, although, as detected by Western immunoblotting, only the levels of proteins recognized by anti-rat CYP3A- and CYP2B antibodies appeared to increase consistently. Also the carboxylesterases and uridindiphosphoglucuronyl-transferase (UGT) activity toward 1-naphthol displayed a similar trend, glutathione S-transferase accepting 3,4-dichloronitrobenzene as a substrate being the only enzyme activity showing an age-related decline. A positive correlation was also found between liver cadmium content and CYP amount as well as the activities of most monooxygenases (except for those related to CYP1A), carboxylesterases, and UGT. While confirming that a number of enzyme activities are less expressed in foals, our results contradict the general view that the drug metabolizing capacity drops in elder individuals. Although several other factors can influence the kinetics of foreign compounds in aged animals, data from this study may provide insight in understanding possible age-related differences in drug efficacy and the response to toxic substances in horses.

Pharmacokinetics of Local Anaesthetics in Infants and Children

Amide local anaesthetics used for regional anaesthesia in paediatric patients are potent sodium channel blockers with marked stereospecificity, which consistently influences their action, especially their toxic action on the heart. At toxic concentrations, they induce severe arrhythmias with the potential for cardiac arrest. These agents are all bound to serum proteins, mainly to alpha(1)-acid glycoprotein (AAG), but also to human serum albumin. Protein binding ranges from 65% (lidocaine) to more than 95% (bupivacaine, ropivacaine). Because AAG is a major acute phase protein, its concentration rapidly increases when inflammatory processes develop, particularly during the postoperative period. Neonates and infants have a lower AAG concentration in serum as compared with adults; therefore, their free fraction of local anaesthetics is increased accordingly. This has important clinical implications since, at least at steady state, the toxic effects of local anaesthetics are directly related to the free (unbound) drug concentration. After injection into the epidural space, absorption into the bloodstream follows a biphasic process. The buffering properties of the epidural space are important and prevent a rapid rise in concentration. In infants and children, the epidural space seems to protect patients in a similar manner. Moreover, it has been observed that the peak plasma concentration (C(max)) of ropivacaine is delayed in infants and children when compared with adults. The time to C(max) decreases from 90-120 minutes in infants aged less than 6 months to 30 minutes in children aged more than 8 years. This delay in C(max) may also be related to the lower clearance observed in younger patients. Local anaesthetics are metabolised by cytochrome P450 (CYP). The main CYP isoforms involved are CYP3A4 for lidocaine and bupivacaine and CYP1A2 for ropivacaine. CYP3A4 is not mature at birth but is partly replaced by CYP3A7. The intrinsic clearance of bupivacaine is only one-third of that in adults at 1 month of age, and two-thirds at 6 months. CYP1A2 is not fully mature before the age of 3 years. Indeed, the clearance of ropivacaine does not reach its maximum before the age of 5 years. However, at birth this clearance is not as low as expected, and ropivacaine may be used even in younger patients.

Serum carbamazepine concentrations in elderly patients: a case-matched pharmacokinetic evaluation based on therapeutic drug monitoring data

PURPOSE

To assess the influence of aging on the steady-state pharmacokinetics of carbamazepine (CBZ) in a large population of patients evaluated in a therapeutic drug monitoring (TDM) setting.

METHODS

The database of a large TDM service was used to identify retrospectively steady-state serum CBZ concentrations in 157 elderly patients with epilepsy (65 years and older) treated with CBZ alone or in combination with phenobarbital (PB). CBZ apparent oral clearance (CL/F) values were calculated and compared with those determined in an equal number of controls aged 20 to 50 years, and matched for gender, body weight, and comedication.

RESULTS

Compared with corresponding controls, mean CBZ CL/F values were 23% and 24% lower, respectively, in the groups of elderly patients receiving monotherapy (57.1 +/- 20.6 vs. 74.6 +/- 28.3 ml/h/kg; p < 0.0001) and PB comedication (74.7 +/- 25.5 vs. 98.7 +/- 34.9 ml/h/kg; p < 0.01). Within each age group, patients comedicated with PB showed significantly higher CBZ CL/F values than those on monotherapy. A negative correlation between CL/F and age was found both within the monotherapy and the PB comedicated groups. In addition, CL/F values showed a positive relation with the administered daily dosage, which persisted within subgroups homogeneous for age and comedication. The independent influence of age, CBZ dosage, and comedication on CBZ CL/F was confirmed by multiple regression analysis.

CONCLUSIONS

CBZ CL/F is decreased in an age-dependent manner in elderly patients compared with younger subjects, presumably because a reduction in the rate of CYP3A4-mediated drug metabolism. Elderly patients retain their sensitivity to dose-dependent autoinduction and to heteroinduction by enzyme-inducing AEDs, but their metabolic rates remain considerably below those observed in matched controls. As a result of this, patients in old age will require lower CBZ dosages to achieve serum concentrations comparable with those found in nonelderly adults.

Differential pharmacokinetics of theophylline in elderly patients

The clinical use of theophylline as a first-line bronchodilator has declined during the last two decades. However, in many clinical settings, such as an emergency bronchial asthma attack, theophylline may have a first-line role, in combination with beta(2)-adrenoreceptor agonists and corticosteroids, for improving the asthmatic status. Furthermore, many therapeutic mechanisms of theophylline for bronchial asthma have been reported, and recent studies have suggested that theophylline therapy may have a beneficial role in the management of chronic stable asthma as well as exacerbated disease. However, theophylline has a low therapeutic index because the bronchodilation it produces has a linear relationship with logarithmic increases in serum concentration for the therapeutic range of 5-20 mg/L. Thus, the knowledge of its basic pharmacokinetics and the factors that can alter its clearance is clinically relevant for physicians. Especially when used in elderly asthmatic patients, dosage adjustment of theophylline is a requisite since the elderly have several risk factors that may increase the plasma theophylline level, such as reduced clearance, various underlying diseases and multiple coadministered drugs. After theophylline treatment has been initiated, therapeutic drug monitoring is required.

Clinically important drug interactions in epilepsy: general features and interactions between antiepileptic drugs

There are two types of interactions between drugs, pharmacokinetic and pharmacodynamic. For antiepileptic drugs (AEDs), pharmacokinetic interactions are the most notable type, but pharmacodynamic interactions involving reciprocal potentiation of pharmacological effects at the site of action are also important. By far the most important pharmacokinetic interactions are those involving cytochrome P450 isoenzymes in hepatic metabolism. Among old generation AEDs, carbamazepine, phenytoin, phenobarbital, and primidone induce the activity of several enzymes involved in drug metabolism, leading to decreased plasma concentration and reduced pharmacological effect of drugs, which are substrates of the same enzymes (eg, tiagabine, valproic acid, lamotrigine, and topiramate). In contrast, the new AEDs gabapentin, lamotrigine, levetiracetam, tiagabine, topiramate, vigabatrin, and zonisamide do not induce the metabolism of other AEDs. Interactions involving enzyme inhibition include the increase in plasma concentrations of lamotrigine and phenobarbital caused by valproic acid. Among AEDs, the least potential interaction is associated with gabapentin and levetiracetam.

Influence of age and cytochrome P450 2C9 genotype on the steady-state disposition of diclofenac and celecoxib

OBJECTIVE

To analyse the influence of age and cytochrome P450 (CYP) 2C9 genotype on the steady-state disposition of the standard NSAID diclofenac and the new COX-2 selective inhibitor celecoxib, both of which are metabolised by the polymorphically expressed CYP2C9.

DESIGN

Double-blind randomised crossover study under steady-state conditions.

SUBJECTS

12 young (age 32 +/- 5 years, bodyweight 71 +/- 12kg; mean +/- SD) and 12 elderly (68 +/- 2 years, 82 +/- 15kg) healthy, drug-free, nonsmoking Caucasians of both sexes.

METHODS

All subjects received oral celecoxib (200mg twice daily) and diclofenac (75mg twice daily) for 15 days separated by a drug-free interval of at least 3 weeks. Following the last morning dose, multiple blood samples were taken for 25 hours. Concentrations of celecoxib and diclofenac were measured by specific and sensitive high performance liquid chromatography. Identification of CYP2C9 genotype was performed by genomic DNA sequencing. Pharmacokinetic parameters for total and unbound drugs were individually analysed by noncompartmental techniques.

RESULTS

For diclofenac, area under the concentration-time curve over the dosage interval (AUC(tau)) was larger in young subjects (3.2 +/- 1.0 mg * h/L) than in older individuals (2.4 +/- 0.4 mg * h/L; p < 0.05). As the terminal half-life (t((1/2)Z)) was very similar in both groups (3.9 +/- 4.4 vs 3.5 +/- 3.3 hours), either less complete absorption in the elderly or their higher bodyweight could account for the difference. For celecoxib, AUC(tau) (5.8 +/- 1.7 vs 5.6 +/- 2.3 mg * h/L) and t((1/2)z) (11.8 +/- 8.7 vs 11.2 +/- 2.9 hours) were almost identical in young and older subjects. Plasma protein binding of both NSAIDs was unaffected by age, and apparent oral clearances for unbound drugs were not different between the two groups of healthy subjects. When considering the genotype of all individuals (CYP2C9*1/*1, n = 10; CYP2C9*1/*2, n = 6; CYP2C9*2/*2, n = 2; CYP2C9*1/*3, n = 4; CYP2C9*3/*3, n = 1), no association with any pharmacokinetic parameter of either drug was apparent. Moreover, there was no significant correlation between the AUC values of celecoxib and diclofenac.

CONCLUSIONS

Age and CYP2C9 genotype do not significantly affect the steady-state disposition of celecoxib and diclofenac. This would indicate that both drugs need no dosage reduction in the elderly (at least up to 75 years) and that, besides CYP2C9, additional CYP species contribute to the elimination of both agents.

Effects of age and the CYP2D6*10 allele on the plasma haloperidol concentration/dose ratio

The authors studied the effect of aging and the CYP2D6*10 polymorphism on the plasma haloperidol (HAL) concentration after chronic administration of HAL. Subjects were 110 Japanese patients (66 male) treated orally with HAL. Venous blood was obtained from each patient for determination of the HAL concentration/dose (C/D) ratio (the plasma concentration of HAL divided by the daily dose of HAL per kilogram body weight) and for CYP2D6 genotyping. Overall, there was a significant linear correlation between the HAL C/D ratio and age. In subgroup analyses, the correlation was significant for patients with non-2D6*10 homozygous genotypes, but not for those with the 2D6*10 homozygous genotype. Overall, the HAL C/D ratio was significantly higher in older subjects (at least 50 years old) than younger ones (less than 50 years old). The ratio was significantly higher in older than in younger subjects for patients with non-2D6*10 homozygous genotypes, but not for those with the 2D6*10 homozygous genotype. Our results indicate that the effect of age on the HAL C/D ratio depends upon the CYP2D6*10 genotype. Because there are racial differences in the CYP2D6 genotype, further studies should investigate age effects on the HAL C/D ratio in different patient populations.

Increased oxidative stress in younger as well as in older humans

BACKGROUND

The free radical theory of aging is based upon the adverse effects of oxidative stress (OS), and indices of OS generally increase with advancing age. However, since OS may also be a normal physiological response in youth, when reactive oxygen species (ROS) act as signal transducers during normal growth and development, we compared markers of OS in normal humans over a wide spectrum of different ages.

METHODS

Fasting breath samples were collected from 102 healthy volunteers (age 9 to 89 years) and volatile organic compounds (VOCs) were assayed by gas chromatography and mass spectroscopy. The intensity of OS in each volunteer was estimated by the breath methylated alkane contour (BMAC), a three-dimensional display of the abundance of C4-C20 alkanes and monomethylated alkanes. The collective abundance of these VOCs in a breath sample was reduced to a single value, the volume under curve (VUC), and correlated with chronological age.

RESULTS

Compared to subjects aged 20-40 years, the mean BMAC VUC was significantly increased in subjects aged < 20 (p < 0.0001) and >40 years (p < 0.001). A cubic function correlated BMAC VUC (x) with chronological age (y): y = 33.7 - 3.29x + 0.072x(2) - 0.0004x(3) (r = 0.48).

CONCLUSIONS

Breath markers of OS were significantly increased both in younger and in older subjects, compared to those aged 20-40 years. Increased OS in older subjects was consistent with previous reports, but increased OS in younger subjects aged < 20 years is a new observation; this may be a normal physiological response in youth.

DNA microarrays and toxicogenomics: applications for ecotoxicology?

Toxicogenomics attempts to define how the regulation and expression of genes mediate the toxicological effects associated with exposure to a chemical. DNA microarrays are rapidly becoming one of the tools of choice for large-scale toxicogenomic studies. An approach in modern toxicogenomics has been to classify toxicity based on gene transcriptional patterns; comparing the transcriptional responses of a chemical with unknown toxicity to those for which the transcriptional profiles and toxicological endpoints have been well characterized. Recent evidence suggests that gene expression microarrays may be instrumental in defining mechanisms of action of toxicants. However, several assumptions are inherent to a toxicogenomic-based approach in toxicology, many of which remain to be validated. Gene expression profiling using DNA microarrays represents a snapshot of the gene transcriptional responses occurring at a particular time and within a particular tissue. Toxicity, on the other hand, represents a continuum of possible effects governed by both temporal and spatial factors that are inextricably contingent upon the exposure conditions. The perceived toxicological properties of any chemical are dependent on the route, dose, and duration of the exposure, and as such, gene expression patterns are also subject to these variables. Correct interpretation of DNA microarray data for the assessment of the toxicological properties of chemicals will require that temporal and spatial gene expression profiles be accounted for. These considerations are further compounded in ecotoxicological studies, during which altered gene expression patterns induced from exposure to an anthropogenic substance must be discernible over and above the complex effects that phenotypic, genotypic, and environmental variables have on gene expression. To this end, the greatest utility of DNA microarrays in the field of ecotoxicology may be in predicting the toxicological modes of action of anthropogenic substances on host physiology, particularly in non-model organisms. Predictable and accurate assessment of the impacts of a chemical substance in ecotoxicology will require that classical toxicological endpoints be used to validate any effects predicted based on gene expression profiling. Validated expression profiling may subsequently find utility in ecotoxicological-based computer simulation models, such as the Biotic Ligand Model (BLM), in which gene expression information may be integrated with geochemical, pharmacokinetic, and physiological data to accurately assess and predict toxicity of metals to aquatic organisms.

Antiepileptic-antipsychotic drug interactions: a critical review of the evidence

The potential for drug-drug interactions in psychiatry and patients with epilepsy is very high. Moreover, antiepileptic drugs are widely used outside epilepsy as psychotropic agents and their spectrum of activity on behavior is of considerable interest to psychopharmacology. In both neurologic and psychiatric practice, pharmacotherapy combinations are commonly used to treat comorbid psychiatric and neurologic disorders, to reduce or control the adverse effects of a medication or to increase its efficacy. This paper focuses on the metabolic pharmacokinetic interactions between two classes of psychotropic drugs: antiepileptic and antipsychotic drugs. The degree of documentation varies for many interactions from clinical case-report experiences to well established research outcomes. The evidence and the clinical significance of these interactions are reviewed. In general, it is better to use as few drugs as possible, as multicolored politherapies increase the possible adverse effects of drug interactions and reduce patient compliance.

Factors contributing to carbamazepine-macrolide interactions

Certain macrolides (e.g. clarithromycin or erythromycin) are known to interact with the carbamazepine antiepileptic drug. Carbamazepine-macrolide interaction leads to an increase in the level of carbamazepine in the blood, so inducing carbamazepine toxicity. The aim of this paper is to compare the extent of the interaction for each macrolide and to study the effects of age, gender, weight, the carbamazepine and macrolide dosages and the use of other antiepileptic drugs on the extent of the carbamazepine-macrolide interaction. Case reports published in the literature were reviewed and analysed to this end. The results show that three macrolides (erythromycin, troleandomycin and, to a lesser extent, clarithromycin) may induce carbamazepine toxicity in clinical practice. Furthermore, it was observed that high dosages of carbamazepine or macrolides and the use of concurrent anticonvulsivant drugs in the case of patients below 60 years of age are associated with the highest carbamazepine levels in carbamazepine-macrolide interactions. This study should help physicians choose a macrolide that does not interact with carbamazepine and evaluate the risk of an interaction between carbamazepine and macrolides.

Increased sensitivity to warfarin in elderly Hispanics

It has been suggested that aging enhances the pharmacologic effect of warfarin, but there is little information about the effects of warfarin in aging minority populations. The authors examine the response of an aging Hispanic population to warfarin. Charts in their anticoagulation clinic were retrospectively examined for the following information: age, sex, weight, duration of anticoagulant therapy, number of medical problems, number of medications, number of minor or major bleeding episodes, prothrombin time, warfarin dose, and international normalized ratio (INR). The dose-adjusted prothrombin time ratio (PTR) and dose-adjusted INR were calculated by dividing the PTR and INR by the mean warfarin dose. Four groups were compared by age: < 50, 50 to 59, 60 to 69, and > or = 70. A total of 243 charts were reviewed: 113 female, 130 male; 90% were Hispanic. The most common indication for anticoagulation was atrial fibrillation. Elderly patients had more medical problems (3.1 vs. 2.4) and took more medications (3.4 vs. 2.4) than younger patients. The dose-adjusted PTR and dose-adjusted INR increased with aging (0.59 vs. 0.38 and 0.85 vs. 0.59, p < .05 ANOVA). In a multiple linear regression analysis, only age remained significantly associated with the anticoagulant effect. These results are consistent with previous reports on the effect of warfarin in aging patients and extend these data to the Hispanic population.

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.