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

The Effect of Different Habitat Types and Ontogenetic Stages on the Diet Shift of a Critically Endangered Fish Species, Coreius guichenoti (Sauvage and Dabry de Thiersant, 1874)

This study examined the effect of habitat types and ontogenetic stages on the diet shift of Coreius guichenoti (Sauvage and Dabry de Thiersant, 1874), a critically endangered fish species. Based on the stable isotope analysis method, the following was explored: the variations in δ¹³C and δ¹⁵N values, isotopic niche width and four basal food sources (Mollusks, Macrocrustaceans, Aquatic insect larvae and particulate organic matters (POMs)) among three essential habitat types (the spawning ground, natural riverine feeding and nursery area, and Three Gorges Reservoir area) and between two ontogenetic stages (immature and fully mature stages). A diet shift associated with habitat type changes was observed, but there were no obvious differences in diet composition between the two ontogenetic stages. Dietary plasticity and a preference for specific foods were the important determinants of feeding behavior through the life history of this species. POM was important for the survival of this species in the resource-limited spawning ground, but this species fed more heavily on higher-order consumers in resource-abundant areas. This study highlights the importance of maintaining free connectivity among different habitats (particularly spawning grounds) to ensure the long-term sustainability of potamodromous fish species as well as the full investigation of all types of critical habitats for understanding the trophic ecology of a single fish species.

Reduced Clearance of Phenobarbital in Advanced Cancer Patients near the End of Life

BACKGROUND AND OBJECTIVES

Little is known about the pharmacokinetics of phenobarbital in terminally ill cancer patients. We investigated whether phenobarbital clearance alters depending on the length of survival.

METHODS

We retrospectively reviewed the clinical, laboratory, and therapeutic drug monitoring (TDM) records of patients who received parenteral or oral phenobarbital for 21 consecutive days or longer between 2000 and 2016. Patients were divided into non-cancer and cancer groups. Cancer patients were further stratified according to the survival interval after TDM: those who survived > 3 months were classified as long-surviving and the remainders short-surviving cancer patients. Phenobarbital clearance (CL_PB) was calculated at steady state. Multiple comparisons of median CL_PB were conducted among the three groups.

RESULTS

Data were collected from 44 non-cancer patients and 34 cancer patients comprising 24 long-surviving and 10 short-surviving cancer patients. Among 10 short-surviving cancer patients, 4 had hepatic metastasis. Median CL_PB (range) in short-surviving cancer patients [0.076 (0.057‒0.114) L/kg/day] was significantly (p < 0.05) lower than that in non-cancer patients [0.105 (0.060‒0.226) L/kg/day] and in long-surviving cancer patients [0.100 (0.082‒0.149) L/kg/day].

CONCLUSION

Terminally ill patients with advanced cancer may have reduced CL_PB, thereby TDM is recommended for these patients particularly near the end of life.

Treatment of epilepsy in postmenopausal women

Menopausal women represent a rapidly growing proportion of the population. Epidemiologic evidence for the increased incidence of epilepsy in elderly patients suggests that with global aging of the population, there is likely to be a growing need for healthcare workers to manage seizures in older women. Unfortunately, there has been relatively little scientific investigation into the unique concerns of postmenopausal woman with epilepsy. There is some evidence that women may experience increased seizure activity during the menopausal transition owing to the effects of estrogen and progesterone on neuronal excitability. During perimenopause and menopause, use of hormone-replacement therapy can also worsen seizure control. Menopausal women are particularly vulnerable to osteoporosis and fragility fractures, both of which demonstrate increased risk following exposure to antiepileptic drugs. Optimization of epilepsy therapy to avoid both seizures and falls caused by antiepileptic drug-induced imbalance is crucial in order to minimize fracture risk in this group of women. Elderly patients are more susceptible to adverse medication side effects owing to drug interactions and the physiologic changes of aging that result in altered drug pharmacokinetics.

Treatment and management of epilepsy in the elderly demented patient

Epilepsy and seizures are more frequent in the elderly population than in any other age group. The number of individuals older than 65 is constantly increasing, and dementia is a process that predominantly affects this age group. Several studies have shown that dementia is an important risk factor for developing seizures and epilepsy. Seizure semiology in the elderly demented might differ from that of younger age groups and diagnosis can be complicated further by the variety of other causes of transient changes of alertness and behavior that affects these patients. The pharmacokinetic changes of antiepileptic drugs in the elderly make this group a major therapeutic challenge. Side effects and drug interactions play a major role in the choice of antiepileptic agents. This review intends to summarize the existing data to see whether this can help guide the clinician in the treatment and management of epilepsy in the elderly patient with dementia. Nonpharmacologic therapeutic options are also briefly considered.

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.

Role of valproate across the ages. Treatment of epilepsy in the elderly

In June 2005, a team of experts participated in a workshop with the objective of reaching agreement on several important aspects of valproate in the treatment of elderly patients with epilepsy. Epilepsy in the elderly is relatively common and its incidence increases for each decade after age 60. The aetiology and manifestations of epilepsies in the elderly are complex because of comorbidity and other underlying risk factors. A consensus was reached that elderly patients who present with a seizure disorder should be referred rapidly to a specialist and that diagnosis should be improved by using a multidisciplinary team of cardiologists, neurologists and epilepsy experts (syncope, falls and seizure specialists). This is especially important to avoid mistreatment with antiepileptic drugs (AEDs). There was consensus that the elderly are generally more susceptible to the adverse effects of AEDs than younger adults. For these reasons, in older persons AEDs should be started at low dosages, and titrated slowly according to clinical response. Some of the most troublesome side effects of AEDs in the elderly include sedation and cognitive side effects, as well as osteoporosis. Drug-drug interactions should be given special consideration. There was consensus that the pharmacokinetics of all AEDs are altered in the elderly, and that the most significant change common to all AEDs is a moderate reduction in renal and metabolic clearance. Predicting pharmacokinetic changes in the individual, however, can be very difficult because multiple factors contribute to a high inter-patient variability. There was agreement on the advantages and disadvantages of the use of valproate in the elderly, and consensus that valproate is a useful option in this population. There was no consensus, however, on whether valproate should be considered among the preferred first-line treatments in the elderly.

The influence of old age and enzyme inducing comedication on the pharmacokinetics of valproic acid at steady-state: A case-matched evaluation based on therapeutic drug monitoring data

PURPOSE

To evaluate the influence of aging on the pharmacokinetics of valproic acid (VPA) at steady-state and on the susceptibility of VPA metabolism to enzyme induction by antiepileptic comedication.

METHODS

The database of the therapeutic drug monitoring service of a large neurological hospital was searched to identify patients aged > or = 65 years stabilized on VPA therapy. Apparent VPA oral clearance (CL/F) calculated for each elderly patient was compared with that determined in an equal number of VPA-treated controls aged 20-50 years and matched for gender, body weight and antiepileptic drug (AED) comedication.

RESULTS

A total of 71 elderly patients aged 70.0+/-4.4 years, including 20 receiving enzyme inducing AEDs, was included in the main evaluation. In the absence of enzyme inducing comedication, VPA CL/F in the elderly was similar to that found in non-elderly controls (9.7+/-4.6 versus 10.2+/-4.6mlh(-1)kg(-1)). Elderly patients on enzyme inducing comedication, on the other hand, had lower CL/F values than enzyme induced younger controls (11.7+/-5.4 versus 16.0+/-6.3mlh(-1)kg(-1), p<0.05). Since VPA CL/F is known to increase with increasing dosage, a lower VPA dosage in elderly patients comedicated with enzyme inducers compared with controls may have contributed to differences in CL/F between the two groups.

CONCLUSIONS

In the absence of enzyme inducing comedication, VPA clearance in the elderly was comparable to that observed in controls. VPA clearance in elderly patients receiving enzyme inducing AEDs was lower than in controls, the difference being probably due to an influence of age as well as to the fact that mean VPA dosage was lower in these patients than in controls. Since our measurements of clearance were based on total serum VPA concentrations and VPA binding to plasma proteins is known to be reduced in old age, it is likely that the clearance of unbound, pharmacologically active, VPA was decreased to an important extent in the elderly, presumably as a result of a decline in drug metabolizing capacity.

Pharmacological and clinical aspects of antiepileptic drug use in the elderly

In this article, epidemiological and clinical aspects related to the use of antiepileptic drugs (AEDs) in the elderly are highlighted. Studies have shown that people with epilepsy receiving AED treatment show important deficits in physical and social functioning compared with age-matched people without epilepsy. To what extent these deficits can be ascribed to epilepsy per se or to the consequences of AED treatment remains to be clarified. The importance of characterizing the effects of AEDs in an elderly population is highlighted by epidemiological surveys indicating that the prevalence of AED use is increased in elderly people, particularly in those living in nursing homes. Both the pharmacokinetics and the pharmacodynamics of AEDs may be altered in old age, which may contribute to the observation that AEDs are among the drug classes most commonly implicated as causing adverse drug reactions in an aged population. Age alone is one of several contributors to alterations in AED response in the elderly; other factors include physical frailty, co-morbidities, dietary influences, and drug interactions. Individualization of dosage, avoidance of unnecessary polypharmacy, and careful observation of clinical response are essential for an effective and safe utilization of AEDs in an elderly population.