© Springer International Publishing Switzerland 2015
Yoo Kuen Chan, Kwee Peng Ng and Debra Si Mui Sim (eds.)Pharmacological Basis of Acute Care10.1007/978-3-319-10386-0_2121. The Elderly Patient
(1)
Department of Anesthesiology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia
Abstract
Many more elderly individuals will present for treatment in acute care now than in the past as the proportion of patients in the geriatric age group increases. Physiological changes in the elderly affect the way their bodies handle and react to various drugs, and this needs to be kept in mind during the management of these patients in acute care. Some pharmacological changes can be predicted while many others remain unknown simply because large randomized controlled trials are difficult to perform in this age group. Many who present in the acute setting may already have medical co-morbidities and be on multiple medications which will increase their risks for drug-drug interactions and associated adverse effects. The pharmacokinetic changes associated with ageing include changes in absorption due to decreased blood flow, altered volume of distribution depending on lipid solubility or water solubility, decreased metabolism and excretion. It is imperative that drug administration in this category of patients is titrated to meet the patients’ needs.
Keywords
ElderlyGeriatricTitration of drugsDecreased metabolismMultiple medicationsDrug interactionsIntroduction
Aging is part of a normal physiological process that transforms many systems in our body. The geriatric group can be difficult to classify by age but it is generally accepted to be 65 years and above. Statistics have shown that our patient population is aging fast and growing in number.
This group of patients tend to have multiple pre-existing medical morbidities which naturally put them at risk of requiring acute and long term medical management. Practitioners who provide acute care to the elderly must consider and understand many pharmacological issues peculiar to them. As with the group of patients in the other extreme of age, the paediatric group, the pharmacokinetics and pharmacodynamics of many drugs in the geriatric population have not been studied sufficiently and their dosing requirements or actions remain predictions based on large randomized trials in a much younger adult population. Age related changes in pharmacokinetics, pharmacodynamics and adverse drug reactions including drug-drug interactions are important issues in the care of this category of patients.
Pharmacokinetic Changes in the Elderly
With aging, the body physiology changes to affect the way a drug becomes absorbed, distributed, metabolized and excreted. These processes form the core principles of pharmacokinetics and explain why a drug behaves differently in the elderly as compared to the younger person. Proper consideration must be applied to every drug that is given to establish and ensure safety in an elderly patient.
Absorption
The gastrointestinal tract (GIT) changes with time and this greatly affects many orally administered drugs. Both the blood flow to and motility of the GIT reduce over time. The production of gastric acid reduces, allowing the pH to rise gradually. These affect gastric transit time and absorption of many drugs, which can be unpredictable in the elderly.
In the acute setting, many resuscitation drugs are given intravenously in the interest of speed and to avoid the problems associated with variability of absorption. If the subcutaneous and intramuscular routes are chosen, then reduced blood flow to the tissues may affect rate of absorption and onset of the drug given.
Distribution
The volume of distribution (Vd) in the body for many types of drugs changes as we grow older. One of the factors contributing to this is protein binding. Older adults produce less albumin, an important binding protein which determines the amount of free drug available for its actions, metabolism and clearance.
The aging process is also associated with lower total body water which results in a smaller Vd for water soluble drugs. The body muscle to fat ratio decreases as muscle mass declines over the years compared to the proportion of body fat. So, in general, drugs distributed in muscle may have a smaller Vd but vice versa for more lipid soluble drugs. Since Vd is an essential component of half life and loading dose, whenever Vd changes, so will both half life and loading dose. Sometimes the changes can be unpredictable. As an example, if Vd falls, the loading dose to achieve a desired drug concentration should also be reduced and the half life will also be altered. If these changes are not taken into consideration, then drug toxicity can easily occur. Many drugs lack precise information on how their Vd will be affected. Resuscitation drugs, sedatives and analgesics need to be given in lower doses and titrated to effect.
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