Pharmacokinetic optimisation of drug therapy in elderly patients

Age and Sex Variation in the Duration of Action and Corneal Touch Threshold (CTT) following Instillation of 0.5% Topical Ophthalmic Proparacaine and Tetracaine Hydrochlorides

PURPOSE

We investigated the effect of age and sex on corneal touch threshold (CTT) and duration of action following administration of 0.5% topical ophthalmic proparacaine and tetracaine hydrochlorides.

METHODS

A prospective, randomized, subject-masked, crossover study design was used. Two hundred and forty human volunteers were enrolled in the study. Corneal touch threshold (CTT) was determined using a Cochet-Bonnet esthesiometer. CTT was measured every 15 seconds for the first 1-minute and at 5-minute intervals subsequently for a period of 40 minutes after the application of each anesthetic. CTT and duration of action of the ophthalmic solutions were tested for statistical significance using repeated measures ANOVA.

RESULTS

The total duration of effect was 20 minutes for females and 25 minutes for males for both anesthetics. The total duration of the effect of both solutions decreased with increasing age; however, elderly participants had the longest duration (5 minutes) of the maximal effect (minimum CTT) of the two ophthalmic preparations. There was a significant influence of sex, F (2.39, 569.65) = 2.86, p=0.04; F (3.48, 828.19) = 4.41, p=0.003, and age, F (4.78, 566.18) = 8.97, p < 0.001; F (7.19, 852.56) = 20.55, p < 0.001 on CTT following application of proparacaine hydrochloride and tetracaine hydrochloride, respectively.

CONCLUSION

CTT and duration of anesthetic effect after instillation of 1 drop of 0.5% proparacaine hydrochloride and 0.5% tetracaine hydrochloride vary based on sex and age.

Identification of the key target profiles underlying the drugs of narrow therapeutic index for treating cancer and cardiovascular disease

An appropriate therapeutic index is crucial for drug discovery and development since narrow therapeutic index (NTI) drugs with slight dosage variation may induce severe adverse drug reactions or potential treatment failure. To date, the shared characteristics underlying the targets of NTI drugs have been explored by several studies, which have been applied to identify potential drug targets. However, the association between the drug therapeutic index and the related disease has not been dissected, which is important for revealing the NTI drug mechanism and optimizing drug design. Therefore, in this study, two classes of disease (cancers and cardiovascular disorders) with the largest number of NTI drugs were selected, and the target property of the corresponding NTI drugs was analyzed. By calculating the biological system profiles and human protein–protein interaction (PPI) network properties of drug targets and adopting an AI-based algorithm, differentiated features between two diseases were discovered to reveal the distinct underlying mechanisms of NTI drugs in different diseases. Consequently, ten shared features and four unique features were identified for both diseases to distinguish NTI from NNTI drug targets. These computational discoveries, as well as the newly found features, suggest that in the clinical study of avoiding narrow therapeutic index in those diseases, the ability of target to be a hub and the efficiency of target signaling in the human PPI network should be considered, and it could thus provide novel guidance in the drug discovery and clinical research process and help to estimate the drug safety of cancer and cardiovascular disease.

The elderly as a sensitive population in environmental exposures: making the case

The US population is aging. CDC has estimated that 20% of all Americans will be 65 or older by the year 2030. As a part of the aging process, the body gradually deteriorates and physiologic and metabolic limitations arise. Changes that occur in organ anatomy and function present challenges for dealing with environmental stressors of all kinds, ranging from temperature regulation to drug metabolism and excretion. The elderly are not just older adults, but rather are individuals with unique challenges and different medical needs than younger adults. The ability of the body to respond to physiological challenge presented by environmental chemicals is dependent upon the health of the organ systems that eliminate those substances from the body. Any compromise in the function of those organ systems may result in a decrease in the body's ability to protect itself from the adverse effects of xenobiotics. To investigate this issue, we performed an organ system-by-organ system review of the effects of human aging and the implications for such aging on susceptibility to drugs and xenobiotics. Birnbaum (1991) reported almost 20 years ago that it was clear that the pharmacokinetic behavior of environmental chemicals is, in many cases, altered during aging. Yet, to date, there is a paucity of data regarding recorded effects of environmental chemicals on elderly individuals. As a result, we have to rely on what is known about the effects of aging and the existing data regarding the metabolism, excretion, and adverse effects of prescription medications in that population to determine whether the elderly might be at greater risk when exposed to environmental substances. With increasing life expectancy, more and more people will confront the problems associated with advancing years. Moreover, although proper diet and exercise may lessen the immediate severity of some aspects of aging, the process will continue to gradually degrade the ability to cope with a variety of injuries and diseases. Thus, the adverse effects of long-term, low-level exposure to environmental substances will have a longer time to be manifested in a physiologically weakened elderly population. When such exposures are coupled with concurrent exposure to prescription medications, the effects could be devastating. Public health officials must be knowledgeable about the sensitivity of the growing elderly population, and ensure that the use of health guidance values (HGVs) for environmental contaminants and other substances give consideration to this physiologically compromised segment of the population.

[Pharmacotherapy of elderly patients]

There is a complex interaction between age-driven changes in physiology and functional limitations in the elderly, which influences the pharmacokinetics, pharmacodynamics and management of drug therapy. Another frequent characteristic is multimorbidity, which results in polypharmacy and is a major cause of adverse drug reactions due to drug-drug interactions. Furthermore there are special risks in the elderly, which may alter the risk-benefit analysis of drug therapy and renal impairment, falls and delirium are of particular significance. These factors are discussed in detail and preventive strategies are given to optimize drug therapy in this population. Furthermore, the risks of frequently prescribed drugs and drugs bearing special risks in the elderly are outlined.

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.

Clinical pharmacology of DP-b99 in healthy volunteers: first administration to humans

AIMS

To investigate the safety, tolerability and pharmacokinetics of DP-b99 in healthy volunteers. DP-b99 is a newly developed lipophilic, cell permeable derivative of BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid), which selectively modulates the distribution of metal ions in hydrophobic milieu, and is in clinical development as a neuroprotectant for cerebral ischaemic stroke. To our knowledge no BAPTA derivative has ever been administered to man. Here we report the first human administration of DP-b99 in a phase I, two-part, double-blind, randomized placebo controlled study, with single IV doses of 0.003-1.0 mg kg(-1) day(-1) DP-b99 (part 1) or multiple ascending doses of 0.03-1.0 mg kg(-1) day(-1) DP-b99 over 4 days (part 2).

METHODS

A double-blind, dose escalating tolerability study of DP-b99 in normal (young - aged between 18 and 40 years and elderly - aged between 65 and 85 years) healthy adult male volunteers was conducted. Part 1 of the study investigated single administration of ascending intravenous doses, and part 2 examined the effects of ascending doses given repeatedly over 4 days. Twenty-four young volunteers in part 1 received single dose administrations and 26 young volunteers in part 2 received repeated ascending dose administrations of either intravenous DP-b99 or placebo. Subsequently, 10 elderly volunteers received repeated intravenous DP-b99 (1 mg kg(-1)) or placebo in part 2 over 4 days. Adverse events were identified by either subject self reporting or based upon laboratory parameters (blood chemistry, complete blood cell count, prothrombin time (PT), activated partial thromboplastin (PTT), physical examination, vital signs (blood pressure, pulse rate, respiratory rate, body temperature) and urinalysis. A comprehensive set of cardiovascular parameters was assessed as well (blood pressure, 12 lead-ECG recordings and continuous bedside cardiac monitoring for 6 h on day 1).

RESULTS

The administration of DP-b99 up to the highest dose of 1.0 mg kg(-1) was well tolerated and had an acceptable safety profile up to the highest dose of 1.0 mg kg(-1) tested in both study parts. No serious or severe adverse events were encountered. Eight mild to moderate adverse events were observed in six of the seven young subjects treated with four repeated doses of 1.0 mg kg(-1), with reversible phlebitis being the most frequently reported adverse event. The drug was tolerated better at the injection site by the elderly group compared with the younger subjects. No adverse effects were observed in cardiovascular parameters sensitive to trans-membranous calcium concentrations. The pharmacokinetic parameters were derived by noncompartmental analysis. On day 1 following administration of 1 mg kg(-1) the mean half-life of DP-b99 in young volunteers was 3.47 +/- 0.90 h and in the elderly was 2.11 +/- 0.09 h. On day 4 following the same administration of DP-b99 the mean half-life was 4.36 +/- 1.49 and 2.10 +/- 1.14 h in the young and elderly, respectively. There was higher systemic exposure in the elderly, for example C(max), had a mean 1.6-fold higher exposure on day 1 (95% CI Lower 0.90, Upper 2.74) and 2.5-fold on day 4 (95%CI 1.70, 3.68). This increase is in line with the presumed central role of hepatic blood flow in the elimination of DP-b99. No accumulation was observed after repeated dosing with 1 mg kg(-1) (mean accumulation calculated by AUC(0, 24 h) (day 4) : AUC(0, 24 h) (day 1) and was observed to be between 0.9 and 1.3 (young, elderly).

CONCLUSIONS

This study suggests that DP-b99 is well tolerated in healthy young and elderly volunteers within the dose range evaluated. Studies to investigate further the efficacy of the compound are in progress.

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.

Phenobarbital Pharmacokinetics in Old Age: A Case-matched Evaluation Based on Therapeutic Drug Monitoring Data

PURPOSE

To assess the influence of aging on the pharmacokinetics of phenobarbital (PB) at steady state in patients receiving long-term therapy.

METHODS

Serum PB concentrations from the database of the therapeutic drug monitoring service of a large neurological hospital were used to calculate apparent clearance values (CL/F) in 224 patients aged 65 years and older (mean, 73 +/- 6.1 years). CL/F values in these patients were compared with those determined in an equal number of controls aged 20 to 50 years (mean, 35.7 +/- 7.9 years) and matched for gender, body weight, and type of anticonvulsant comedication. Correlations of CL/F with age, body weight, gender, and comedication also were explored within each age group.

RESULTS

PB CL/F values were significantly lower in elderly patients than in controls (3.2 +/- 0.8 vs. 4.1 +/- 1.2 ml/h/kg; p < 0.0001). Age was identified as a statistically significant predictor of CL/F at multiple regression analysis, but it accounted for only a modest component of the interindividual pharmacokinetic variation. Comedication with carbamazepine (CBZ) and phenytoin (PHT) was associated with a moderate decrease in PB CL/F, which reached statistical significance in the elderly group (p < 0.01 for CBZ comedication; p < 0.001 for PHT comedication).

CONCLUSIONS

Aging is associated with a significant decrease in PB clearance, which might be related to a reduction in glomerular filtration rate or diminished drug-metabolizing capacity in the liver or both. Because of this, older patients will require lower dosages to achieve serum PB concentrations comparable with those found in nonelderly adults.

An approach to drug induced delirium in the elderly

Drugs have been associated with the development of delirium in the elderly. Successful treatment of delirium depends on identifying the reversible contributing factors, and drugs are the most common reversible cause of delirium. Anticholinergic medications, benzodiazepines, and narcotics in high doses are common causes of drug induced delirium. This article provides an approach for clinicians to prevent, recognise, and manage drug induced delirium. It also reviews the mechanisms for this condition, especially the neurotransmitter imbalances involving acetylcholine, dopamine, and gamma aminobutyric acid and discusses the age related changes that may contribute to altered pharmacological effects which have a role in delirium. Specific interventions for high risk elderly with the goal of preventing drug induced delirium are discussed.

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.

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.

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.

Prescribing of psychotropics in the elderly: why is it so often inappropriate?

Psychotropic medications are an important treatment approach to mental health disorders; such disorders are common in the elderly population. Elderly patients are more likely to experience adverse effects from these agents than their younger counterparts due to age-related changes in pharmacodynamic and pharmacokinetic parameters. Because of these factors, inappropriate use of psychotropic medications in elderly patients has become a focus of concern. In general an agent is considered inappropriate if the risk associated with its use exceeds its benefit. Implicit and explicit criteria for inappropriate use of medications in the elderly have been created and include psychotropic agents. These criteria vary in their make-up but the explicit criteria tend to agree that amitriptyline, doxepin, and benzodiazepines that have long half-lives are not appropriate. Although explicit inappropriate medication criteria have been in existence since 1991, elderly patients continue to receive inappropriate psychotropic medications. A wide array of factors may be responsible for this practice. Provider-related causes include deficits in knowledge, confusion due to the lack of a consensus on the inappropriate psychotropic criteria, difficulties in addressing an inappropriate medication started by a previous provider, multiple prescribers and pharmacies involved in the care of a patient, negative perceptions regarding aging, and cost issues. Patients may contribute to the problem by demanding an inappropriate medication. Finally, the healthcare setting may inadvertently contribute to inappropriate prescribing by such policies as restrictive formularies or lack of reimbursement for pharmacists' clinical services. Successful approaches to optimising prescribing have been either educational or administrative. Educational approaches (e.g. one-on-one sessions, academic detailing) seek to influence decision making, while administrative approaches attempt to enforce policies to curtail the undesired practice. The US Omnibus Budget Reconciliation Act of 1987, which improved psychotropic medication use in long-term care, is an excellent example of administrative intervention. More research specifically focused on the causes of inappropriate psychotropic medication use and methods to avoid this practice is needed before targeted recommendations can be made.

Cilomilast: pharmacokinetic and pharmacodynamic interactions with digoxin

BACKGROUND

Cilomilast is an orally active, selective phosphodiesterase 4 inhibitor currently in clinical development for the treatment of chronic obstructive pulmonary disease.

OBJECTIVE

The purpose of this study was to examine the tolerability and steady-state pharmacokinetics of cilomilast and digoxin when coadministered at standard therapeutic doses in healthy adults.

METHODS

In an initial, open-label phase, healthy young adults received cilomilast 15 mg BID for 5 days. After a 7-day washout period, subjects entered a double-blind, crossover phase during which they received oral digoxin (375 microg once daily) for 2 consecutive 14-day periods with no intervening washout period. Cilomilast 15 mg BID or placebo was coadministered during the first 14-day period. Subjects then crossed over to the alternative treatment for the second 14-day period. Blood and urine samples were collected at appropriate times for evaluation of digoxin and cilomilast steady-state pharmacokinetic parameters. The size of the study was sufficient to achieve 90% power to correctly exclude an effect of cilomilast.

RESULTS

Twelve of the 16 subjects enrolled completed the study. There were 4 withdrawals--1 due to noncompliance, 1 due to a positive drug screening, and 2 due to adverse events. At steady state, cilomilast 15 mg BID had no significant effect on the steady-state pharmacokinetic parameters of digoxin, with 90% CIs for both primary end points--area under the plasma concentration-time curve (AUC) over a 24-hour dosing interval and minimum plasma concentration--completely contained within the specified interval for equivalence (0.80-1.25). A mean reduction in maximum observed plasma concentration of digoxin of 11% was observed during coadministration with cilomilast, and time to maximum concentration was delayed by a median of 1 hour, suggesting a small reduction in the rate of digoxin absorption. Digoxin did not appear to markedly affect cilomilast steady-state pharmacokinetics. The most frequently reported adverse event was headache.

CONCLUSIONS

Cilomilast 15 mg BID had no clinically significant effect on steady-state AUC or on predose trough plasma concentrations of digoxin (375 microg once daily). The steady-state pharmacokinetics of cilomilast 15 mg BID were similar whether administered alone or with digoxin at steady state (375 microg once daily).

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.

Clinical Effectiveness of Sertraline Three Times a Week Compared with Once-Daily Regimen

Objective:

To evaluate the clinical effectiveness of sertraline three-times-a-week regimen in community nursing home residents who were stabilized on sertraline once-daily regimen for ≥12 weeks for management of depression.

Methods:

All residents with diagnosis of depression stabilized on sertraline once-daily for ≥12 weeks for management of depression were entered into the study. After assessing depression at baseline by the 30-item Geriatric Depression Scale (GDS), 17-item Hamilton Depression Scale (HAM-D), and a five-item Clinical Global Impression Scale (CGI), the treatment regimen of all residents was changed to equivalent doses of sertraline three times a week. Depression was reassessed at 12 weeks by the GDS, HAM-D, and CGI scales.

Results:

Forty-four residents of a community nursing home participated in the study. Their mean ± SD age was 83 ± 12 years; there were 13 men and 31 women. Depression scores at baseline and after the three-times-weekly regimen was initiated were GDS (7.7 ± 0.9 vs. 7.4 ± 0.6), HAM (4.3 ± 0.5 vs. 4.2 ± 0.4), and CGI (3.0 ± 0.5 vs. 3.0 ± 0.4). Mean daily sertraline cost was $1.88 ± 0.4 before and $0.76 after the change in regimen.

Conclusions:

Our results indicate that sertraline three times weekly is as clinically effective as the once-daily regimen in the management of depression in our population of nursing home residents and achieves significant cost savings.

Taste effects of lingual application of cardiovascular medications

Medications used to treat cardiovascular diseases such as congestive heart failure, high blood pressure, and arrhythmia, are prescribed extensively in Western countries. However, taste complaints are common side effects of many of these cardiovascular medications. Although clinical observations are helpful in determining potential taste problems from a medication, experimental studies are necessary to obtain quantitative data on taste. In the studies performed here, nine cardiovascular medications (labetalol HCl, captopril, diltiazem HCl, enalapril maleate, hydrochlorothiazide, propranolol HCl, mexiletine HCl, procainamide HCl, and propafenone HCl) were applied to the tongue in human volunteers to measure the direct effect of these drugs on taste receptors. The medications were applied topically to the tongue surface of both young and elderly subjects to mimic the situation in which the drug is secreted into the saliva. Detection thresholds ranged from 0.048 mM (propafenone) to 0.438 mM (procainamide). The detection thresholds of healthy elderly subjects did not significantly differ from young controls. The compounds tested had a predominantly bitter taste with other qualities as well. In addition, topical application of the medications to the tongue affected the taste of one or more taste stimuli, with medications differing in the pattern of taste effects exhibited. The mechanism of taste effects is not fully known, but the results of this study suggest one route may be due to medications' effect on peripheral taste receptors.

Effect of aging on beta-adrenergically mediated thermogenesis in men

The age-dependent alterations in beta-adrenergically mediated thermogenesis were investigated in 11 young (mean +/- SE age: 21.9 +/- 0.5 yr) and 9 older (52.9 +/- 2.1 yr) men during intravenous infusion of the nonselective beta-agonist isoprenaline (Iso). The older men had higher basal plasma norepinephrine (327.7 +/- 35.8 vs. 159.0 +/- 18.2 pg/ml, P < 0.001) and epinephrine (75.1 +/- 18.1 vs. 29.1 +/- 5.3 pg/ml, P < 0.05) concentrations than the young. The beta-adrenergically mediated thermogenesis was diminished in the older men, as reflected by the significantly higher plasma Iso concentration needed to increase resting energy expenditure by 15% (236.1 +/- 51.0 vs. 107.6 +/- 11.4 pg/ml, P < 0.05). Additionally, both dose (39.4 +/- 6.6 vs. 19.1 +/- 1.5 ng . kg fat-free mass-1 . min-1, P < 0.01) and plasma concentration (332.2 +/- 59.1 vs. 119.3 +/- 14.0 pg/ml, P < 0.01) of Iso needed to increase resting heart rate by 25 beats/min were higher in older than in younger subjects, suggesting that the age-related decline in beta-adrenergic sensitivity is a generalized defect not related to a specific tissue or response. In conclusion, aging is associated with a diminished beta-adrenergically mediated thermogenesis. This blunted thermogenic response may contribute to a positive energy balance and thus promote increased fat storage and obesity.

Pharmacokinetics and the pharmacodynamic action of midazolam in young and elderly patients undergoing tooth extraction

OBJECTIVE

To determine whether age-dependent pharmacokinetic and pharmacodynamic alterations account for a more pronounced response to benzodiazepines among elderly patients.

METHODS

Twelve young patients and 10 elderly patients received an intravenous dose of 0.05 or 0.03 mg/kg midazolan, respectively, before third molar extraction. Postoperative pain was treated with 30 mg dihydrocodeine. Serum concentrations of midazolam and sedative effects were monitored with visual analog scales and choice reaction time measurements for 6 hours. Test values above baseline were integrated, and pharmacokinetic-pharmacodynamic analysis was performed. Heart rate, blood pressure, arterial oxygen saturation, and amnesia also were assessed.

RESULTS

There were no significant age-dependent differences in disposition of midazolam between young and elderly patients (apparent volume of distribution, 1.3 +/- 0.2 versus 1.1 +/- 0.4 L/kg; halflife, 3.3 +/- 1.5 hours versus 3.7 +/- 2.2 hours; total body clearance, 451 +/- 186 ml/min versus 343 +/- 137 ml/min). However, higher values of area under the effect curve (AUEC) and AUEC divided by area under the serum concentration-time curve (AUC) (sensitivity index) were observed among the elderly as follows: AUEC for reaction time (AUECRT) (573 versus 261; p = 0.042), AUEC for visual analog scale (AUECVAS) (37.7 versus 14.4; p = 0.011), AUECRT/AUC (6.3 versus 1.8; p = 0.007), and AUECVAS/AUC (0.40 versus 0.11; p = 0.009) compared with the young group. Likewise, mean concentration at half-maximal effect for sedation was lower (p = 0.025) among older patients (20.5 +/- 2.2 ng/ml) than among younger (29.7 +/- 6.6 ng/ml) patients. Amnesia was observed among 86% of patients and oxygen saturation was always 95% or more of basal value. There were no age-related differences in concentration of dihydrocodeine and its active metabolite dihydromorphine, but dihydromorphone levels were much lower in there intermediate metabolizers (455 to 879 fmol/l) and especially in five poor metabolizers (65 to 498 fmol/L) than among extensive metabolizer of cytochrome p450 2D6 (1604 to 6490 fmol/L).

CONCLUSION

Elderly patients are more sensitive to the sedative action of midazolam than young patients, and the sensitivity is caused by age-dependent pharmacodynamic alterations. The age-adjusted doses used are both effective (for sedative amnesia) and safe (in terms of arterial oxygen saturation, heart rate, and blood pressure.

Optimal treatment of heart failure in the elderly

Heart failure is a common condition in the elderly and one that is likely to become more prevalent as the population ages. Many drugs have been developed for the treatment of heart failure, but because clinical trials of these agents have often not included elderly patients their results need to be extrapolated from younger to older patients. Age-related physiological changes that affect how the available treatments are used occur in many organ systems. Effective management strategies can be implemented in elderly patients as well as in younger age groups, and these can improve both functional status and quality of life as well as reducing hospital admission and improving survival. This article reviews the physiological changes that occur in the elderly and the treatment approach that can be taken in elderly patients with heart failure.

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.

Pharmacokinetic optimisation in the treatment of Parkinson's disease

The current symptomatic treatment of Parkinson's disease mainly relies on agents which are able to restore dopaminergic transmission in the nigrostriatal pathway, such as the dopamine precursor levodopa or direct agonists of dopamine receptors. Ancillary strategies include the use of anticholinergic and antiglutamatergic agents or inhibitors of cerebral dopamine catabolism, such as monoamine oxidase type B inhibitors. Levodopa is the most widely used and effective drug. Its peculiar pharmacokinetics are characterised by an extensive presystemic metabolism, overcome by the combined use of extracerebral inhibitors of the enzyme aromatic-amino acid decarboxylase and rapid adsorption in the proximal small bowel by a saturable facilitated transport system shared with other large neutral amino acids. Drug transport from plasma to the brain is mediated by the same carriers operating in the intestinal mucosa. The main strategies to assure reproducibility of both drug intestinal absorption and delivery to the brain and clinical effect include standardisation of levodopa administration with respect to meal times and a controlled dietary protein intake. The levodopa plasma half-life is very short, resulting in marked plasma drug concentration fluctuations which are matched, as the disease progresses, with swings in the therapeutic response ('wearing-off' phenomena). 'Wearing-off' phenomena can be also associated, at the more advanced disease stages with a 'negative', both parkinsonism-exacerbating and dyskinetic effect of levodopa at subtherapeutic plasma concentrations. Dyskinesias may be also related to high-levodopa, excessive plasma concentrations. Recognition of the different levodopa toxic response patterns can be difficult on a clinical basis alone, and simultaneous monitoring of levodopa concentration-effect relationships may prove useful to disclose the underlying mechanism and in planning the correct pharmacokinetic management. Controlled-release levodopa formulations have been developed in an attempt to smooth out fluctuations in plasma profiles and matched therapeutic responses. The delayed levodopa absorption and lower plasma concentrations which characterise controlled-release formulations compared with standard forms must be taken into account when prescribing dosage regimens and can be complicating factors in the management of the advanced disease stages. The pharmacokinetic and pharmacodynamic characterisation of the other antiparkinsonian agents is hampered by the lack of sensitive and specific analytical methods to measure their very low plasma drug concentrations and by the difficulty in quantitatively assessing overall moderate drug clinical effects. In clinical practice an optimal dosage schedule is still generally found for each patient on an empirical basis. Future strategies should focus on the search for pharmacological agents with a better kinetic profile, particularly a higher and reproducible bioavailability and a predictable relationship between plasma drug concentration and clinical response. Treatments aimed not only at controlling the symptoms, but also at slowing the neurodegenerative process, are currently under intensive investigation.