Plasma protein binding of drugs in the elderly

Examining Whole Blood, Total and Free Plasma Tacrolimus in Elderly Kidney Transplant Recipients

BACKGROUND

Therapeutic monitoring is routinely performed to ensure tacrolimus whole-blood concentrations fall within a predefined target. Despite this, patients still experience inefficacy and toxicity that could be related to variability in free (unbound) tacrolimus exposure. Therefore, the aim of this study was to compare tacrolimus-free plasma (C u ), total plasma (C p ), and whole-blood (C wb ) concentrations in adult kidney transplant recipients and to characterize tacrolimus disposition across different matrices.

METHODS

Twelve-hour concentration-time profiling was performed in 15 recipients, allowing simultaneous measurement of C u , C p , and C wb . Pharmacokinetic parameters were estimated using noncompartmental analysis. The relationship between C wb and C p were examined using a capacity-limited binding model, incorporating the hematocrit fraction ( fHCT ) to estimate maximum binding concentration ( Bmax ) and dissociation constant ( Kd ). The relationship between C p and C u was evaluated using a linear binding model to estimate the nonspecific binding parameter ( Nplasma ). Nonlinear regression analysis was used to obtain estimates of Bmax , Kd , and Nplasma .

RESULTS

A total of 195 paired C wb , C p , and C u values were collected. The median ratios of C wb :C p , C p :C u , and C wb :C u were 9:1, 20:1, and 138:1, respectively. Variability in free plasma exposure was large; free trough values ranged from 8 to 51 ng/L and free area-under-the-concentration-time-curve values ranged from 424 to 7160 ng·h/L. Median (range) estimates of Bmax , Kd , and Nplasma were 90.4 µg/L (22.4-752.5 µg/L), 2.36 µg/L (0-69.2 µg/L), and 0.05 (0.035-0.085), respectively. The interindividual variability (CV%) in binding parameters was considerable ( Bmax 117.2%; Nplasma 32.5%).

CONCLUSIONS

Large variability was observed in tacrolimus-free plasma exposure and binding parameters. Future research to characterize the relationship between tacrolimus C u and patient outcomes may be of benefit.

Impact of Changes in Free Concentrations and Drug-Protein Binding on Drug Dosing Regimens in Special Populations and Disease States

Over the last few decades, scientists and clinicians have often focused their attention on the unbound fraction of drugs as an indicator of efficacy and the eventual outcome of drug treatments for specific illnesses. Typically, the total drug concentration (bound and unbound) in plasma is used in clinical trials to assess a compound's efficacy. However, the free concentration of a drug tends to be more closely related to its activity and interaction with the body. Thus far, measuring the unbound concentration has been a challenge. Several mechanistic models have attempted to solve this problem by estimating the free drug fraction from available data such as total drug and binding protein concentrations. The aims of this review are first, to give an overview of the methods that have been used to date to calculate the unbound drug fraction. Second, to assess the pharmacokinetic parameters affected by changes in drug protein binding in special populations such as pediatrics, the elderly, pregnancy, and obesity. Third, to review alterations in drug protein binding in some selected disease states and how these changes impact the clinical outcomes for the patients; the disease states include critical illnesses, transplantation, renal failure, chronic kidney disease, and epilepsy. And finally, to discuss how various disease states shift the ratio of unbound to total drug and the consequences of such shifts on dosing adjustments and reaching the therapeutic target.

Impact of the clinical frailty scale on clinical outcomes and bleeding events in patients with ST-segment elevation myocardial infarction

The Clinical Frailty Scale (CFS) is a simple tool to assess patients' frailty and may help to predict adverse outcomes in elderly patients. The aim of the present study was to examine the impact of CFS on clinical outcomes and bleeding events after successful percutaneous coronary intervention (PCI) in ST-segment elevation myocardial infarction (STEMI). We enrolled 266 consecutive patients with STEMI who underwent primary PCI in between January 2015 and June 2018. Patients were categorized into two groups based on the CFS stages: CFS 1-3 and CFS ≥ 4. We collected the data and evaluated the relationship between the CFS grade and the incidence of major adverse cardiovascular events (MACE) and Bleeding Academic Research Consortium 3 or 5 bleeding events. Of these patients, CFS ≥ 4 was present in 59 (22.2%). During the follow-up, 37.3% in the CFS ≥ 4 group and 8.2% in the CFS 1-3 group experienced MACE. In Kaplan-Meier analysis, the proportion of MACE-free survival for 4 years was significantly lower in the CFS ≥ 4 group (log-rank P < 0.001). Additionally, the proportion of bleeding event-free survival was significantly lower in the CFS ≥ 4 group (log-rank P < 0.001). The CFS (per 1-grade increase) remained an independent significant predictor of MACE on multivariate Cox proportional hazard analysis [hazard ratio 1.39 (95% confidence interval: 1.08 to 1.79, P = 0.01)]. In conclusion, CFS was an independent predictor of future adverse cardiac events in patients with STEMI. Therefore, the assessment of CFS is crucial in this population.

Frailty and Bleeding in Older Adults Undergoing TAVR or SAVR: Insights From the FRAILTY-AVR Study

OBJECTIVES

The aim of this study was to examine the value of frailty to predict in-hospital major bleeding and determine its impact on mid-term mortality following transcatheter (TAVR) or surgical (SAVR) aortic valve replacement.

BACKGROUND

Bleeding complications are harbingers of mortality and major morbidity in patients undergoing TAVR or SAVR. Despite the high prevalence of frailty in this population, little is known about its effects on bleeding risk.

METHODS

A post hoc analysis was performed of the multinational FRAILTY-AVR (Frailty Aortic Valve Replacement) cohort study, which prospectively enrolled older adults ≥70 years of age undergoing TAVR or SAVR. Trained researchers assessed frailty using a questionnaire and physical performance battery pre-procedure and ascertained clinical data from the electronic health record. The primary endpoint was major or life-threatening bleeding during the index hospitalization, and the secondary endpoint was units of packed red blood cells transfused.

RESULTS

The cohort consisted of 1,195 patients with a mean age of 81.3 ± 6.0 years. The incidence of life-threatening bleeding, major bleeding with a clinically apparent source, and major bleeding without a clinically apparent source was, respectively, 3%, 6%, and 9% in the TAVR group and 8%, 10%, and 31% in the SAVR group. Frailty measured using the Essential Frailty Toolset was an independent predictor of major bleeding and packed red blood cell transfusions in both groups. Major bleeding was associated with a 3-fold increase in 1-year mortality following TAVR (odds ratio: 3.40; 95% confidence interval: 2.22 to 5.21) and SAVR (odds ratio: 2.79; 95% confidence interval: 1.25 to 6.21).

CONCLUSIONS

Frailty is associated with post-procedural major bleeding in older adults undergoing TAVR and SAVR, which is in turn associated with a higher risk for mid-term mortality.

Therapeutic Drug Monitoring of Antiepileptic Drugs in Epilepsy: A 2018 Update

BACKGROUND

Antiepileptic drugs (AEDs) are the mainstay of epilepsy treatment. Since 1989, 18 new AEDs have been licensed for clinical use and there are now 27 licensed AEDs in total for the treatment of patients with epilepsy. Furthermore, several AEDs are also used for the management of other medical conditions, for example, pain and bipolar disorder. This has led to an increasingly widespread application of therapeutic drug monitoring (TDM) of AEDs, making AEDs among the most common medications for which TDM is performed. The aim of this review is to provide an overview of the indications for AED TDM, to provide key information for each individual AED in terms of the drug's prescribing indications, key pharmacokinetic characteristics, associated drug-drug pharmacokinetic interactions, and the value and the intricacies of TDM for each AED. The concept of the reference range is discussed as well as practical issues such as choice of sample types (total versus free concentrations in blood versus saliva) and sample collection and processing.

METHODS

The present review is based on published articles and searches in PubMed and Google Scholar, last searched in March 2018, in addition to references from relevant articles.

RESULTS

In total, 171 relevant references were identified and used to prepare this review.

CONCLUSIONS

TDM provides a pragmatic approach to epilepsy care, in that bespoke dose adjustments are undertaken based on drug concentrations so as to optimize clinical outcome. For the older first-generation AEDs (carbamazepine, ethosuximide, phenobarbital, phenytoin, primidone, and valproic acid), much data have accumulated in this regard. However, this is occurring increasingly for the new AEDs (brivaracetam, eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, piracetam, pregabalin, rufinamide, stiripentol, sulthiame, tiagabine, topiramate, vigabatrin, and zonisamide).

Pharmacokinetic and pharmacodynamic considerations in the treatment of the elderly patient with hypertension

INTRODUCTION

Hypertension is an important risk factor for developing cardiovascular diseases. It is more prevalent in the elderly population. Recently updated American and European guidelines recommend treating every elderly patient with hypertension independent of age, starting with a low dose of antihypertensive drugs. However, little information is available on the optimal dosages of antihypertensive drugs to treat the elderly safely. Areas covered: Comorbidities, co-medication and frailty status can alter the clinical outcome of drug treatment and can cause adverse events in the elderly. Also, due to pharmacokinetic and pharmacodynamic changes the interpatient variability when using antihypertensive drugs is considerable. In this review, an overview is given on the extent to which the previously mentioned parameters are changed in elderly patients and what this means for the exposure to antihypertensive medication. Also, recommendations on the starting dose of the most frequently used antihypertensive drugs are given based on literature data. Expert opinion: We believe that recommendations on starting dosages followed by a stepwise increase of dosages will lead to improved blood pressure control and less adverse drug reactions in the elderly patient. This may improve adherence to antihypertensive therapy.

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.

Alteration of human serum albumin binding properties induced by modifications: A review

Albumin, a major transporting protein in the blood, is the main target of modification that affects the binding of drugs to Sudlow's site I and II. These modification of serum protein moderates its physiological function, and works as a biomarker of some diseases. The main goal of the paper was to explain the possible alteration of human serum albumin binding properties induced by modifications such as glycation, oxidation and ageing, their origin, methods of evaluation and positive and negative meaning described by significant researchers.

Effect of lipid emulsion infusion on paliperidone pharmacokinetics in the acute overdose rat model: A potential emergency treatment for paliperidone intoxication

Paliperidone prolongs cardiac repolarization in a concentration-dependent manner. Meanwhile, continuous infusion of intravenous lipid emulsion (ILE) has been established as a detoxification therapy for lipophilic drugs. However, this change in pharmacokinetics of various drugs following ILE administration remains to be clarified. Our objective is to clarify the effect of continuous infusion of ILE on the pharmacokinetics of overdosed paliperidone in rats. Paliperidone (20mg/kg) was administered orally to free-moving male Wistar rats. Continuous infusion (initial loading dose: 4ml/kg for 10min, followed by 4ml/kg/h for 12h) of ILE or acetated Ringer's solution (AR) was initiated 30min after paliperidone administration. Plasma concentration profile of paliperidone was monitored for 12h after administration. The plasma concentration and tissue/plasma concentration ratios of paliperidone were compared between ILE and AR groups. The rat group infused with ILE showed a higher area under the concentration-time curve (mean [S.D.]: 6102 [900.9] vs. 3407 [992.1]nghml^-1, p=0.02) and longer elimination half-time (t_1/2) (4.1 [0.9] vs. 2.2 [0.4]h, p=0.02) compared with the AR group. Tissue/plasma concentration ratios of paliperidone were lower in ILE rats than in AR rats (1.98 [0.70] vs. 3.82 [1.47] in the heart, p=0.04; 0.28 [0.29] vs. 1.27 [0.58] in the brain, p<0.001). In conclusion, continuous infusion of ILE would reduce tissue distribution and prolonged the t_1/2 of paliperidone in rats. These results suggest that continuous infusion of ILE has potential as an emergency treatment for acute paliperidone intoxication.

Therapeutic drug monitoring of antiepileptic drugs by use of saliva

Blood (serum/plasma) antiepileptic drug (AED) therapeutic drug monitoring (TDM) has proven to be an invaluable surrogate marker for individualizing and optimizing the drug management of patients with epilepsy. Since 1989, there has been an exponential increase in AEDs with 23 currently licensed for clinical use, and recently, there has been renewed and extensive interest in the use of saliva as an alternative matrix for AED TDM. The advantages of saliva include the fact that for many AEDs it reflects the free (pharmacologically active) concentration in serum; it is readily sampled, can be sampled repetitively, and sampling is noninvasive; does not require the expertise of a phlebotomist; and is preferred by many patients, particularly children and the elderly. For each AED, this review summarizes the key pharmacokinetic characteristics relevant to the practice of TDM, discusses the use of other biological matrices with particular emphasis on saliva and the evidence that saliva concentration reflects those in serum. Also discussed are the indications for salivary AED TDM, the key factors to consider when saliva sampling is to be undertaken, and finally, a practical protocol is described so as to enable AED TDM to be applied optimally and effectively in the clinical setting. Overall, there is compelling evidence that salivary TDM can be usefully applied so as to optimize the treatment of epilepsy with carbamazepine, clobazam, ethosuximide, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, phenobarbital, phenytoin, primidone, topiramate, and zonisamide. Salivary TDM of valproic acid is probably not helpful, whereas for clonazepam, eslicarbazepine acetate, felbamate, pregabalin, retigabine, rufinamide, stiripentol, tiagabine, and vigabatrin, the data are sparse or nonexistent.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Quantification of total and unbound concentrations of lorazepam, oxazepam and temazepam in human plasma by ultrafiltration and LC-MS/MS

BACKGROUND

A fast and sensitive assay for quantifying total and unbound concentrations of lorazepam (Lzp), oxazepam (Ozp) and temazepam (Tzp) in human plasma was needed for a plasma protein binding study.

RESULTS

Plasma samples were precipitated with acetonitrile for determination of total concentrations or subjected to ultrafiltration for determination of unbound concentrations. An LC-MS/MS assay was developed with an Allure® PFP propyl column and a mobile phase of 35% acetonitrile/0.1% formic acid over 4.5 min and ESI+-MS/MS detection. Matrix effects were negligible in plasma and approximately 70% in ultrafiltrate but were accounted for by the internal standards Lzp-d₄, Ozp-d₅ and Tzp-d₅. The assay was validated for total concentrations of 10-100 ng/ml Lzp, 200-2000 ng/ml Ozp and 100-1000 ng/ml Tzp, and for unbound concentrations of 1-10 ng/ml Lzp, 20-200 ng/ml Ozp and 10-100 ng/ml Tzp. Precision was <14% CV and accuracy was 96-110% throughout the calibration range. The mean precision of triplicate analysis of 60 study samples was <4% CV for total and <8% CV for unbound concentrations.

CONCLUSION

A fast and sensitive assay was developed and validated. It has been applied successfully to a protein binding study.

Epilepsy in the elderly

The elderly, often defined as those 65 years or older, are the most rapidly growing segment of the population, and onset of epilepsy is higher in this age group than in any other. This paper reviews recent developments, including a new proposed definition of epilepsy, a transgenic mouse model of Alzheimer's disease that exhibits complex partial seizures, evidence that the highest incidence of epilepsy may occur after admission to a nursing home, a challenge to the vitamin D hypothesis of osteoporosis associated with antiepileptic drugs (AEDs), evidence that the genetic complement of hepatic isoenzymes is more predictive of metabolic rate than age, and data showing that there is considerable variability in serum levels of AEDs in many nursing home residents during constant dosing conditions.

Disposition of flurbiprofen in man: influence of stereochemistry and age

1. The stereoselective metabolism and pharmacokinetics of the enantiomers of flurbiprofen were investigated following the oral administration of the racemic drug (100 mg) to four young and four elderly healthy volunteers (two males and two females per group). 2. The stereochemical composition of the drug and the 4'-hydroxy- metabolite in serum and the drug, 4'-hydroxy- and 3'-hydroxy-4'-methoxy- metabolites, both free and conjugated, in urine were determined by a direct chromatographic method of enantiomeric analysis. 3. Modest enantioselectivity in clearance (CL S/R: young, 0.86; elderly, 0.88) was largely responsible for the apparent elimination half-life of (S)-flurbiprofen being significantly greater (p<0.01) than that of the R-enantiomer in both age groups (young, S: 5.2 +/- 0.7 versus R: 4.5 +/- 0.6 h; elderly, S: 9.6 +/- 1.2 versus R: 7.1 +/- 1.0 h). The serum concentrations of 4'-hydroxyflurbiprofen were five- to 20-fold lower than those of the corresponding drug enantiomers, stereoselective disposition being evident in the significantly greater (p<0.05) apparent half-lives of the S- compared with the R-enantiomer in both groups (young, S: 10.6 +/- 2.4 versus R: 6.7 +/- 1.1 h; elderly, S: 13.7 +/- 1.7 versus R: 10.2 +/- 1.2 h). 4. Some 60 and 72% of the dose was excreted in 24-h urine in elderly and young volunteers, respectively, a significantly greater (p<0.05) proportion of which was of the R-configuration in both age groups (S/R: young, 0.87; elderly, 0.81). The major urinary excretion products were flurbiprofen and 4'-hydroxyflurbiprofen, and their acyl-conjugates in both groups. 5. Age-associated differences in the pharmacokinetics of flurbiprofen occurred in a non-stereoselective manner and were primarily as a consequence of a significant approximately 40% decrease (p<0.01) in clearance of both enantiomers in the elderly due to reduced metabolic activity. Consequently, the elderly had greater exposure to both enantiomers, as reflected by the AUCs(0-inf) being significantly higher (p<0.05), by 60%, in this age group compared with the young. 6. The findings suggest that age-related alterations in the disposition of flurbiprofen could have significant implications for the use of the drug in the elderly.

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.

Strategies to assess the drug interaction potential in translational medicine

Translational medicine is the drug development phase in which preclinical and clinical applied research is conducted to aid dose and disease selection with great financial impact. Thus, during this phase, early discontinuation of a drug that will later fail due to drug interactions is a must for a proper resource allocation. It is not only important to identify a potential interaction, but also to be able to differentiate between detectable interactions and clinically relevant interactions. Due to the scientific advancement, the prediction of drug interactions during translational medicine has shifted from empirical/observational to rational based. These investigations are thus in line with the FDA's Critical Path Initiative and are facilitated by the availability of mature technologies and by current European and US guidelines for both in vitro and in vivo studies. Because drug interactions must be evaluated in a multidisciplinary fashion, even if these studies are contracted externally, pharmaceutical companies should be directly involved in the conduction of such studies to fully exploit their potential and to allow a better and faster interpretation of the results.

Epilepsy in the Elderly

The elderly are the most rapidly growing segment of the population and the incidence of epilepsy is higher in the elderly than in any other age group. They have been subdivided into the "young old," 65-74 years, "middle old" 75-84 years, and the "old old," 85 years or older. But further subdivisions are needed: persons with only epilepsy, those with epilepsy and multiple medical problems, and the frail elderly. Thus, when considering therapy, one must tailor the interventions to nine categories: young old healthy, young old with medical problems, frail young old, old healthy, old with medical problems, frail old, old old healthy, old old with medical problems, and frail old old. The prevalence of antiepileptic drug (AED) use in community dwelling elderly is 1.5%; in the nursing home population it is 10%. Surprisingly, 3% have an AED newly prescribed after admission. Overall, 6.2% were using phenytoin, 1.8% carbamazepine, 0.9% valproic acid, 1.7% phenobarbital, and others combined, 1.2%. AEDs rank fifth among all drug categories as a cause of adverse reactions. There are very few data regarding the clinical use of AEDs in the elderly. The paucity of information makes it very difficult to recommend specific AEDs with any confidence that the outcomes will be optimal. An appropriate for elderly healthy may not be appropriate for elderly with multiple medical problems, and in frail elderly variable absorption may be a major problem. One of the major advantages of some newer AEDs is lack of drug interactions. Cost is an advantage of the older AEDs. Regardless of the AED chosen, one must use doses appropriate to the clearance of the drug, and AED levels, especially unbound (free) levels, must be monitored. The elderly nursing home resident may be more frail, be taking many medications, and have several concomitant illnesses, making them difficult to treat. The most commonly used AED, phenytoin, may not be the easiest or safest AED to prescribe in the elderly with multiple medical problems or the frail elderly.

Pharmacokinetics in older persons

BACKGROUND

Physiologic changes and disease-related alterations in organ function occur with aging. These changes can affect drug pharmacokinetics in older persons.

OBJECTIVE

This article reviews age-related changes in pharmacokinetics and their clinical relevance.

METHODS

A PubMed search was conducted using the terms elderly and pharmacokinetics. Other reviews were also included for literature searching. The review includes literature in particular from 1990 through April 2004. Some articles from before 1990 were included to help illustrate principles of age-related pharmacokinetics.

RESULTS

There are minor changes in drug absorption with aging. The effect of aging on small-bowel transporter systems is not yet fully established. Bioavailability of highly extracted drugs often is increased with age. Transdermal absorption may be delayed, especially in the case of water-soluble compounds. Fat-soluble drugs may distribute more widely and water-soluble drugs less extensively in older persons. Hepatic drug metabolism shows wide interindividual variation, and in many cases, there is an age-related decline in elimination of metabolized drugs, particularly those eliminated by the cytochrome enzyme system. Any decrement in cytochrome enzyme metabolism appears nonselective. Synthetic conjugation metabolism is less affected by age. Pseudocapillarization of the sinusoidal endothelium in the liver, restricting oxygen diffusion, and the decline in liver size and liver blood flow may influence age-related changes in rate of hepatic metabolism. Frailty, physiological stress, and illness are important predictors of drug metabolism in older individuals. Inhibition of drug metabolism is not altered with aging, but induction is reduced in a minority of studies. Renal drug elimination typically declines with age, commensurate with the fall in creatinine clearance. Renal tubular organic acid transport may decline with age, while the function of the organic base transporter is preserved but may be less responsive to stimulation.

CONCLUSION

Changes in pharmacokinetics occur due to age-related physiologic perturbations. These changes contribute to altered dose requirements in older persons, particularly in the case of drugs eliminated by the kidney. Interindividual variation, disease, frailty, and stress may overshadow age-related changes.

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.

Pharmacology of anticancer drugs in the elderly population

Modifications to bodily functions and physiology are known to occur with age. These changes can have a considerable impact on the pharmacokinetic processes of absorption, distribution, metabolism and excretion and the pharmacodynamic properties of administered drugs. For many drugs with a high therapeutic index, this will be clinically unimportant, but for anticancer drugs, which usually have a low therapeutic index, these pharmacological changes can lead to dramatic consequences, such as excessive drug concentrations and unacceptable toxicity, or subtherapeutic drug concentrations and ineffective treatment. Despite the increased susceptibility of the elderly to these changes, doses are rarely adapted on the basis of pharmacokinetics and pharmacodynamics, with the exception of changes secondary to altered renal function. Until recently, only a few large prospective randomised trials have provided evidence-based data for dose adaptations in elderly patients. However, with increasing knowledge of the pharmacokinetics of anticancer drugs, advances in the knowledge of pharmacokinetic behaviour with aging, and documented efficacy and toxicity data in the elderly population, it is possible to highlight aspects of prescribing anticancer drugs in the elderly. In general, and for most drugs, age itself is not a contraindication to full-dose chemotherapy. The main limiting factors are comorbidity and poor functional status, which may be present in a significant number of the elderly population. Elderly patients with cancer are part of the daily practice of oncologists, but currently clinicians can often only estimate whether dose modification is advantageous for the elderly. This review attempts to elucidate the factors that can influence the pharmacokinetics of anticancer drugs frequently used in the elderly, and the clinical or biochemical parameters that form the basis for dose adjustments with age.

Seizures in elderly patients with dementia: epidemiology and management

Epileptic seizures occur in patients with dementia at a higher prevalence than among healthy elderly individuals. The incidence of seizures among patients with dementia varies with the aetiology of the dementing illness. In patients with Alzheimer's disease (the most common form of dementia), approximately 10-22% have at least one unprovoked seizure. Seizures usually occur in later stages of Alzheimer's disease, on average, > or =6 years into the course of the disease. Seizures in Alzheimer's disease are more likely to occur with early-onset disease, particularly if there is a familial presenilin I mutation. The incidence of seizures in other dementing diseases is less clear. There are special considerations regarding the management of seizures in the elderly with dementia. First, the presence of cognitive impairment may impede an accurate diagnosis of seizures. Clinicians may also mistake seizure manifestations for symptoms of the underlying dementia. Second, since most dementia patients are elderly, there are pharmacokinetic changes with aging that affect the use of antiepileptic drugs. Third, antiepileptic drugs have potential cognitive adverse effects that may worsen dementia. Although few studies are available, extrapolations from research in young people and elderly patients without dementia provide several recommendations for the management of seizures in patients with dementia: exclude symptomatic causes of seizures before committing to antiepileptic drug therapy; treat after a first seizure if there is evidence of focal neurological involvement or a risk of recurrent seizures; use antiepileptic drugs with minimal cognitive adverse effects, such as carbamazepine, valproic acid, gabapentin and lamotrigine; and use the lowest possible dosage and monitor antiepileptic drug levels, where possible.

Regional Anaesthesia in the Elderly

The number of elderly patients presenting for anaesthesia and surgery has increased exponentially in recent years. Regional anaesthesia is frequently used in elderly patients undergoing surgery. Although the type of anaesthesia (general versus regional anaesthesia) has no substantial effect on perioperative morbidity and mortality in any age group; it intuitively makes sense that elderly patients would benefit from regional anaesthesia because they remain minimally sedated throughout the procedures and awaken with excellent postoperative pain control. However, a multitude of factors influence the outcome, such as the type, duration and invasiveness of the operation, co-existing medical and mental status of the patient and the skill and expertise of the anaesthesiologist and surgeon. These factors make it difficult to decide if and when one technique is equivocally better than another. Thus, it is more important to optimise the overall management of the patient during the perioperative period and, in most cases, it is the quality of the anaesthetic administered rather than the type of anaesthetic which is most important. Sedatives used for regional anaesthesia in the elderly should be short acting, easy to administer, have a low adverse effect profile and high safety margin. Midazolam, lorazepam, ketamine, propofol and low-dose opioids have been successfully used for sedation in the elderly. Aging affects the pharmacokinetics and pharmacodynamics of local anaesthetics, composition and characteristics of tissues and organs within the body, and physiological functions of the body. Changes in the systematic absorption, distribution and clearance of local anaesthetics lead to an increased sensitivity, decreased dose requirement and a change in the onset and duration of action in the elderly. Decreases in neural population, neural conduction velocity and inter-Schwann cell distance can lead to an increased sensitivity to local anaesthetics in the elderly. The addition of an opioid and epinephrine (adrenaline) has been shown to be useful in central neuraxial blockade. Epinephrine also can prolong the duration of peripheral nerve blocks. However, caution must be exercised as epinephrine has the potential for causing ischaemic neurotoxicity in peripheral nerves. Regional anaesthesia appears to be safe and beneficial in elderly patients; however, every anaesthetic administered must be assessed on a case-by-case basis and particular consideration should be given to the health status of the patient, the operation being performed and the expertise of the anaesthesiologist.

Principles of drug therapy for the elderly patient

Physicians will treat larger numbers of elderly patients as the US population ages. Being treated simultaneously for more than 1 condition with multiple prescription drugs is only 1 reason why elderly patients are at greater risk of experiencing adverse drug reactions. The need for physicians to minimize the incidence of these reactions has become incumbent on both physicians and administrators. We review the underlying reasons why the elderly population is at risk of adverse drug reactions and summarize the principles of drug-drug interaction, metabolism, and distribution, which can help elderly patients receive proper pharmacological treatment.

Epilepsy: comorbidity in the elderly

Elderly people experience the highest incidence of epilepsy and their clinical mananagement is often challenging, due to a potential increase in the likelihood of adverse treatment events. In addition, concomitant diseases are highly prevalent in this population and elderly patients are likely to be prescribed a number of medications that must be taken concurrently. As a result, the incidence of adverse drug-drug interactions and adverse drug reactions is also extremely high. Thus, the treatment of elderly patients with epilepsy requires careful consideration of any comorbid conditions and concomitant medications. Most adverse events are drug-related and are therefore preventable. It is important to consider these complications when prescribing antiepileptic drug (AED) treatment. An AED with broad-spectrum efficacy, good tolerability and a favourable drug interaction profile (e.g. valproate, gabapentin and lamotrigine) may prevent many unwanted drug interactions and side effects.

Gabapentin in geriatric mania

There is little available information on anticonvulsant treatment of mania in elderly patients. Seven elderly patients, each in a manic episode, were treated with gabapentin. All 7 patients experienced improvement in manic symptoms, with minimal to no side effects. They received gabapentin in combination with antipsychotic medications, and in 1 case in combination with valproate. Gabapentin appears to be a safe and effective treatment in geriatric mania when combined with antipsychotic medications or valproate. Gabapentin appears to be well tolerated with no major adverse drug interactions or side effects in elderly manic patients. This case series suggests that controlled studies are warranted to examine gabapentin's efficacy and side effects, particularly as an adjunctive medication, in geriatric mania.

Development and validation of a 96-well equilibrium dialysis apparatus for measuring plasma protein binding

A 96-well equilibrium dialysis block was designed and constructed that is compatible with most standard 96-well format laboratory supplies and instruments. The unique design of the dialysis apparatus allows one to dispense and aspirate from either or both the sample and dialysate sides from the top of the apparatus, which is not possible with systems currently on the market. This feature permits the investigator to analyze a large number of samples, time points, or replicates in the same experiment. The novel alignment of the dialysis membrane vertically in the well maximizes the surface-to-volume ratio, eliminates problems associated with trapped air pockets, and allows one to add or remove samples independently or all at once. Furthermore, the design of the apparatus allows both the sample and dialysate sides of the dialysis well to be accessible by robotic systems, so assays can be readily automated. Teflon construction is used to minimize nonspecific binding of test samples to the apparatus. The device is reusable, easily assembled, and can be shaken in controlled temperature environments to decrease the time required to reach equilibrium as well as facilitate dissolution of test compounds. Plasma protein binding values obtained for 10 diverse compounds using standard dialysis equipment and the 96-well dialysis block validates this method.

A prediction model for polypharmacy: are older, educated women more susceptible to an adverse drug event?

INTRODUCTION

This study attempts to account for variation in the number of prescription medications concurrently consumed in geriatric populations.

METHODS

Data were selected from The National Health and Nutrition Examination Survey, III, 1988-1994 (NHANES III), Adult Household Questionnaire, a complex, multistage, clustered sampling of civilian, non-institutionalized populations, which included a volunteer sample of 5,249 individuals aged 65 and older who participated in NHANES III survey, representing four broad geographic regions and twelve states.

RESULTS

Age, income, and educational level accounted for nine percent of the variation in the number of prescription medications concurrently taken (p < 0.0001); though non-significant, there were gender differences regarding polypharmacy; in addition, there were significant differences with respect to educational levels by region and age by region (p < 0.05).

CONCLUSIONS

Educational level accounted for the most variation in polypharmacy. Women, on average, consumed more prescription medications than men. Older, more educated women may be most likely to engage in polypharmaceutical consumption, suggesting a greater likelihood of an adverse drug event.

Strategies for optimizing antiepileptic drug therapy in elderly people

The elderly take more antiepileptic drugs (AEDs) than all other adults. This extensive use directly correlates with an increased prevalence of epilepsy in a growing population of older people, as well as other neuropsychiatric conditions such as neuropathic pain and behavioral disorders associated with dementia and for which AEDs are administered. The agents account for nearly 10% of all adverse drug reactions in the elderly and are the fourth leading cause of adverse drug reactions in nursing home residents. Numerous factors associated with advanced age contribute to the high frequency of untoward drug effects in this population; however, strategies are available to ensure optimal outcomes.

Epilepsy in the elderly

The active prevalence rate of epilepsy among persons over 65 years of age is approximately 1.5%, about twice the rate in younger adults. Treatment of epilepsy in the elderly is complicated by alterations in drug metabolism, use of concomitant medications, and multiple medical problems. Drug interactions are a major issue, and a full knowledge of the isoenzyme profile and protein-binding characteristics of each drug (antiepileptic and other) must be known.

Oral anticoagulants. Pharmacologic issues for use in the elderly

There has been a marked expansion of the indications for oral anticoagulant therapy, particularly among the elderly. Despite the documented benefits, the use of warfarin remains strikingly low among patients 80 years of age and older. Elderly patients often exhibit an enhanced dose response to warfarin. On average, steady-state warfarin doses decrease by 11% per decade of age. Pharmacokinetic changes in the elderly are negligible. Pharmacodynamic differences have not been well characterized. Initiating warfarin dosing in the elderly should be done cautiously, with doses of 5 mg or less. Doses should be adjusted downward in the presence of congestive heart failure, advanced obstructive lung disease, liver disease, malignancy, protracted diarrhea, enteral feedings, or concurrent potentiating medications. Numerous medications interfere with the anticoagulant response of warfarin. The most powerful potentiating drugs are those that interfere with the metabolism of (S)-warfarin. Examples include amiodarone, trimethoprim-sulfamethoxazole, and metronidazole. These drugs should be prescribed with caution in the elderly and mandate frequent INR monitoring during the induction period. An extensive assessment of patient-specific factors that might increase the hazards related to warfarin therapy needs to be conducted and documented before initiating oral anticoagulant therapy. Patients and their caregivers need to understand the risks and benefits, and to recognize signs of abnormal bleeding and the need for frequent monitoring. Patients should be encouraged to maintain consistency in their vitamin K intake and should strive to meet the recommended dietary allowance for vitamin K. To improve anticoagulation control, physicians and other health care providers need to be aware of the many warfarin drug interactions and be cognizant of the increased dose response of warfarin seen in the elderly. Concurrent prescription of multiple drugs known to affect warfarin's anticoagulant response should be minimized and use of nonselective nonsteroidal anti-inflammatory drugs should be limited given their deleterious effects on the gastric mucosa. Transitions from inpatient care to subacute care and back to outpatient care are particularly vulnerable periods for patients' anticoagulation control. Enhanced provider communication and more seamless transitions help to ensure optimal INR follow-up and timely warfarin dose adjustment if indicated.

Geropharmacology for the rheumatologist

Drug administration to older patients with rheumatic disease is a challenge because they are more likely to have adverse drug reactions compared with younger patients. Elderly patients are at risk for adverse drug effects because they often have multiple acute and chronic illnesses and are on several prescription and over-the-counter medications. This article will enhance the practitioner's understanding of how disease and age modulate the pharmacokinetics and pharmacodynamics of medications commonly prescribed for rheumatic disorders. Minimizing the number of drugs prescribed, starting medications at low doses and increasing slowly, and monitoring for toxicity are especially important in the elderly. With judicious use of medications, the quality of life of older patients with rheumatic disease can be enhanced.

The Geriatric Patient: General Physiologic and Pharmacologic Considerations

The elderly patient is not simply an older adult and needs to have drug therapy applied with caution with regard to the physiologic changes associated with aging that impact the pharmacology and pharmacokinetics of medicinals used in this population. The elderly patient has a number of physiologic changes with age that affect metabolism, distribution, and excretion. In addition, there exists information that demonstrates changes in the pharmacodynamics of drug therapy commonly used in the elderly. This article reviews these changes.

Conventional and new antidepressant drugs in the elderly

Depression in the elderly is nowadays a predominant health care problem, mainly due to the progressive aging of the population. It results from psychosocial stress, polypathology, as well as some biochemical changes which occur in the aged brain and can lead to cognitive impairments, increased symptoms from medical illness, higher utilization of health care services and increased rates of suicide and nonsuicide mortality. Therefore, it is very important to make an early diagnosis and a suitable pharmacological treatment, not only for resolving the acute episode, but also for preventing relapse and enhancing the quality of life. Age-related changes in pharmacokinetics and in pharmacodynamics have to be kept into account before prescribing an antidepressant therapy in an old patient. In this paper some of the most important and tolerated drugs in the elderly are reviewed. Tricyclic antidepressants have to be used carefully for their important side effects. Nortriptyline, amytriptiline, clomipramine and desipramine as well, seem to be the best tolerated tricyclics in old people. Second generation antidepressants are preferred for the elderly and those patients with heart disease as they have milder side effects and are less toxic in overdose and include the so called atypicals, such as selective serotonin reuptake inhibitors, serotonin noradrenalene reuptake inhibitors and noradrenaline reuptake inhibitors. Monoamine oxidase (MAO) inhibitors are useful drugs in resistant forms of depression in which the above mentioned drugs have no efficacy; the last generation drugs (reversible MAO inhibitors), such as meclobemide, seem to be very successful. Mood stabilizing drugs are widely used for preventing recurrences of depression and for preventing and treating bipolar illness. They include lithium, which is sometimes used especially to prevent recurrence of depression, even if its use is limited in old patients for its side effects, the anticonvulsants carbamazepine and valproic acid. Putative last generation mood stabilizing drugs include the dihydropyridine L-type calcium channel blockers and the anticonvulsants phenytoin, lamotrigine, gabapentin and topiramate, which have unique mechanisms of action and also merit further systematic study. Psychotherapy is often used as an adjunct to pharmacotherapy, while electroconvulsant therapy is used only in the elderly patients with severe depression, high risk of suicide or drug resistant forms.

Age-related alteration of carbamazepine-serum protein binding in man

To determine whether biological maturation influences the kinetics of carbamazepine-serum protein binding, the carbamazepine free fraction (%) was investigated in the serum of 66 patients, ranging from 4 to 83 years, with epilepsy or trigeminal neuralgia, treated with carbamazepine alone or carbamazepine in combination with phenytoin, phenobarbital, and/or valproic acid, over a relatively long period. Biochemical parameters such as levels of albumin and non-glycated albumin showed a significant relationship with carbamazepine free fraction (r = -0.521, P < 0.001 for albumin; r = -0.700, P < 0.001 for non-glycated albumin). Non-glycated albumin was more strongly correlated with carbamazepine free fraction. The biochemical parameters showed a significant relationship with age (r =-0.243, P < 0.1 for albumin; r =0.666, P < 0.001 for glycated albumin; r = -0.459, P < 0.001 for non-glycated albumin; r = 0.640, P < 0.001 for carbamazepine free fraction). Glycated albumin (%), non-glycated albumin and carbamazepine free fraction (%) were strongly correlated with age, whereas albumin showed only a weak correlation with age. To evaluate the effects of ageing on carbamazepine-serum protein binding, the patients were divided into three groups according to age: children, 4-15 years; adults, 16-64 years; elderly, 65-83 years. Albumin and non-glycated albumin were much lower, and glycated albumin (%) and carbamazepine free fraction (%) much higher in the elderly group than in the other two groups. The results of this study showed that the major ligand of carbamazepine in the serum was non-glycated albumin, which decreased with age. These observations suggested that in elderly patients, the elevation of free carbamazepine concentrations in the serum caused by reduced non-glycated albumin levels, induces increases in the sensitivity of the pharmacological effects of carbamazepine and the risk of drug interactions.

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.

The aging liver. Drug clearance and an oxygen diffusion barrier hypothesis

A change in drug clearance with age is considered an important factor in determining the high prevalence of adverse drug reactions associated with prescribing medications for the elderly. Despite this, no general principles have been available to guide drug administration in the elderly, although a substantial body of clearance and metabolism data has been generated in humans and experimental animals. A review of age-related change in drug clearances established that patterns of change are not simply explained in terms of hepatic blood flow, hepatic mass and protein binding changes. In particular, the maintained clearance of drugs subject to conjugation processes while oxygen-dependent metabolism declines, and all in vitro tests of enzyme function have been normal, requires new explanations. Reduction in hepatic oxygen diffusion as part of a general change in hepatocyte surface membrane permeability and conformation does provide one explanation for the paradoxical patterns of drug metabolism, and increased hepatocyte volume would also modify oxygen diffusion path lengths (the 'oxygen diffusion barrier' hypothesis). The reduction in clearances of high extraction drugs does correlate with observed reduction in hepatic perfusion. Dosage guidelines emerge from these considerations. The dosage of high clearance drugs should be reduced by approximately 40% in the elderly while the dosage of low clearance drugs should be reduced by approximately 30%, unless the compound is principally subject to conjugation mechanisms. If the hepatocyte diffusion barrier hypothesis is substantiated, this concept may lead to therapeutic (preventative and/or restorative) approaches to increased hepatocyte oxygenation in the elderly. This may lead to approaches for modification of the aging process in the liver.

Standards of laboratory practice: analgesic drug monitoring

Analgesics are the most commonly consumed over-the-counter preparations in the United States. They are used in the treatment of various pain syndromes and other medical conditions. Although analgesics are generally perceived to be safe agents, serious toxicity may occur in the setting of acute overdose, chronic abuse, or overuse. The indications for therapeutic drug monitoring in patients using these medications appropriately is as yet not well defined. The emphasis of this discussion, therefore, is on recommendations for monitoring in situations where toxicity is suspected. Preanalytical, analytical, and practice issues including drug interactions, frequency of monitoring, pertinent ancillary tests, reporting, and special patient groups at risk for toxicity are reviewed. Recent information from a major manufacturer of evacuated tubes arguing against the use of gel tubes for blood collection for drug monitoring is included. Colorimetric/enzymatic/immunoassays for the routine/stat monitoring of acetaminophen and salicylate and diflunisal cross-reactivity with most of the currently used salicylate assays are presented. Achiral and chiral chromatographic assays and newly introduced columns such as restricted access media and/or automated chromatographic systems are reviewed for the analysis of ibuprofen, naproxen, and the recently introduced tramadol. Finally, concepts regarding future directions including drug chirality and chiral analysis are presented.

Antidepressant drugs in the elderly

1. In this article some of the most important and tolerated drugs in the elderly are reviewed. 2. Tricyclic antidepressants have to be used carefully because of their important side effects. Nortriptyline and desipramine appear to be the best tolerated tricyclics in old people. 3. Second generation antidepressants are preferred for the elderly and those patients with heart disease as they have milder side effects and are less toxic in overdose. 4. MAO inhibitors are useful drugs in resistant forms of depression in which the above mentioned drugs have no efficacy and the last generation drugs (reversible MAO inhibitors), such as moclobemide, seem to be very successful. 5. Lithium is sometimes used especially to prevent recurrence of depression, even if its use is limited in old patients due to its side effects. 6. Psychotherapy is often used as an adjunct to pharmacotherapy, while electroconvulsant therapy is used only in the elderly patients with severe depression, high risk of suicide, or drug-resistant forms.

Antiepileptic drug therapy in the elderly

Populations are aging, and the incidence of epilepsy is increased in the elderly population. These demographic facts emphasize the importance of understanding the use of antiepileptic drugs in older patients. Healthy elderly have expected alterations in renal blood flow, hepatic volume and function, and alterations in fat-to-lean ratio of body composition. All of these changes make elderly patients vulnerable to dose-related adverse effects of the standard antiepileptic drugs. Newly developed compounds without enzyme induction effects and renal routes of excretion may be more favorable for use in elderly patients.

Anticonvulsant therapy in aged patients. Clinical pharmacokinetic considerations

Alterations in drug disposition that occur with aging are now becoming widely recognised, and there is an increasing number of drugs for which the approach to therapy in elderly patients can be based on pharmacokinetic data. Both healthy aging and comorbid disease can alter the responsiveness of the body to drugs and to their absorption, distribution and elimination. Altered absorption in the elderly has not been documented after oral ingestion of any anticonvulsant drug. Increased adipose tissue in the elderly may raise the apparent volume of distribution (Vd) of lipid-soluble drugs. An increased Vd in the elderly has been shown for diazepam and clobazam, but not midazolam. The data are inconclusive for phenytoin and valproic acid (sodium valproate). The decreased plasma protein binding that often occurs in the elderly has few clinical consequences. The reduced liver function that to occur with aging seems to affect the elimination of drugs that are mainly cleared by oxidative metabolism [e.g. carbamazepine, phenytoin and phenobarbital (phenobarbitone)]. Reduced clearances for methylphenobarbital (methylphenobarbitone), diazepam, midazolam and clobazam occur in elderly men, but not in women. The reduced renal function that is seen in old age affects the disposition of drugs that are eliminated mainly by direct renal excretion. Thus. the clearances of vigabatrin and gabapentin correlate with creatinine clearance. Such considerations may help guide anticonvulsant dosage in the elderly.

Pharmacodynamic and pharmacokinetic considerations in geriatric psychopharmacology

Age-associated decreases in metabolism and elimination of drugs are sufficient to give one pause before prescribing drugs in the elderly particularly if multiple drugs are to be used. When one factors in concomitant drugs that may inhibit P450-mediated metabolism of other more toxic drugs, genetic deficiency of P450 enzymes, and medical illnesses such as liver and renal failure that will lead to further elevation of drug levels and delay in drug clearance, the likelihood of adverse events when multiple drugs are used in the elderly becomes truly dizzying. In consideration of the pharmacologic principles discussed, when prescribing drugs in the elderly, one might add to the often heard recommendation, "Start low and go slow," a third admonition, "Keep it as simple as possible!"

Management of epilepsy in the elderly

Epilepsy in elderly patients is a growing worldwide challenge; as the population ages, the prevalence of epilepsy increases. Management of epilepsy in elderly patients requires an understanding of their unique medical and pharmacologic characteristics. Accurate assessment of seizures, thorough neurologic assessment to define etiology, and evaluation of concomitant illnesses and living situations are necessary for comprehensive treatment planning and informed management. Expect elderly patients to present challenges to treatment that include concomitant diseases, obligatory polypharmacy with accompanying drug interactions, and age-related changes in renal and hepatic physiology that alter drug metabolism and elimination. Elderly patients have declining intellectual function, motor impairment, or altered special sensory function that make them susceptible to dose-related CNS side effects of antiepileptic drugs (AEDs). When AEDs are added to the medical regimen of an elderly patient, the physician must review all prescribed drugs. Drugs prescribed for concomitant illnesses such as behavioral problems, cardiovascular disease, hypertension, and infection may alter the distribution and metabolism of AEDs, with an impact on efficacy and occurrence of adverse effects. AEDs tend to induce metabolism of other drugs, leading to a decline in target response. Optimal care of elderly patients with epilepsy includes use of free levels to monitor AED concentrations, careful dose selection, and physician sensitivity to patients' social problems.

Inverse nonlinear pharmacokinetics of total and protein unbound drug (oxaprozin): clinical and pharmacokinetic implications

The nonsteroidal antiinflammatory drug oxaprozin is extensively bound to plasma proteins in a concentration-dependent manner. This study demonstrates for the first time the inverse nonlinear pharmacokinetics of total and unbound oxaprozin and presents clinical implications of this phenomenon. A total of 71 healthy volunteers participated in single- and multiple-dose studies. In study I, 0.6-, 1.2-, and 1.8-gm doses of oxaprozin were given on an empty stomach in a randomized, crossover trial (n = 35). In studies II and III, 1.2- and 1.8-gm doses, respectively, were given once a day for 8 days (n = 12 and 24, respectively). Serial blood samples for total and unbound drug assays were taken over a 240-hour period in study I and for a 24-hour period on days 1, 5, and 8 in studies II and III. After administration of 1.2 gm once daily, steady-state conditions were established by day 5. Actual average steady-state plasma concentrations (Cavg) were lower than those predicted from the single-dose study based on linear kinetics for the total drug, but higher for the unbound drug. Nonlinear changes in Vd/F were also noted with multiple-dose administration. Vd/F increased by 47% for total drug but decreased by 61% for unbound drug relative to single-dose values. Half-lives after single-dose administration for total and unbound drug determined from 24 to 240 hours and from 24 to 72 hours, respectively, were dose independent for total drug, but dose dependent for unbound drug. Half-lives after multiple-dose administration measured from 24 to 48 hours in study II decreased further. In conclusion, oxaprozin clearance for the total drug was increased while that of the unbound drug was decreased after repetitive dosing. This inverse pharmacokinetic behavior has been attributed to the two noncompensatory kinetic effects: concentration-dependent protein binding and saturable metabolism of oxaprozin.