Medication Interactions in the Geriatric Population Explained

Introduction to Geriatric Medicine and Aging Demographics

Geriatric medicine, generally referred to simply as "geriatrics," is a branch of internal medicine and healthcare that focuses primarily on the diagnosis, prevention, care, and treatment of disease and disability in elderly patients. Elderly patients are those senior members of the population who have developed a disability or are suffering from a disease that is a result of old age or represents a characteristic symptom of aging. Geriatrics commonly involves treatment of age-related symptoms and disabilities such as deteriorated memory, immobility, and impaired vision and hearing.

In modern times, geriatrics is quite advanced. Specialized services such as psycho-geriatrics — where expert psychologists focus on treating old-age-related depression, memory loss, and other psychological conditions occurring in the elderly — have emerged alongside physical therapy centers whose primary focus is the rehabilitation of diseased and uncomfortable older patients. The main aim of geriatric medicine is to relieve the senior population of the discomforts that old age brings and to promote the general good health of the elderly.

The demographics of the world are changing. For example, as of the 2012 demographic, the United States consists of an aging population — that is, there is an increasing elder patient base (Population Reference Bureau, 2012). According to a report by the United States Department of Health and Human Services, between 2010 and 2030 there will be an increase in the senior population of approximately 73% (Administration on Aging, U.S. Department of Health and Human Services, 2004). Hence, within a span of 30 to 40 years, the world's currently younger countries will experience a growing need for geriatric services.

It should be borne in mind that as the demand for geriatrics rises around the globe, there will be pressure to develop new medicines and methods to cope with old-age diseases and disabilities. However, not all new treatments will benefit the elderly, as the senior population has certain physiological limitations and can develop adverse reactions to drugs that would otherwise be well tolerated by younger individuals.

Physiological Changes of Aging and Their Impact on Drug Pharmacokinetics

As a human being ages, changes occur in all organ systems. Such physiological changes limit the activity of the individual and can cause sometimes severe drug reactions from medications that were intended to ease discomfort. Not only are there internal consequences of aging, but external ones as well. Skin visibly deteriorates with age, losing its tone and elasticity due to changes in elastin and collagen in the epidermis, transforming the outer layer of the body into a sagging, paper-thin sheath. Internal physiological changes, however, tend to affect an individual's lifestyle more significantly.

Numerous internal changes occur across each organ system of the human body. These include degenerative changes that inhibit locomotion through loss of muscle mass and weakening of the joints. Even the cardiac muscle functions at a diminished pace, contributing to high blood pressure and other heart-related diseases such as blocked coronary arteries (Kannel & Gordon, 1978). As a result of lower heart function, the lungs display impaired functionality in terms of gas exchange. Impaired functionality also extends to the liver, kidneys, and digestive system, manifesting as consistent rises in blood glucose levels, osteoporosis, atrophic gastritis, urinary incontinence, reduction in kidney size and mass, and decreased intestinal motility, among others. In women, the occurrence of menopause is universal. All such changes lead to alterations in the metabolism of an elderly individual, meaning that the response to a specific drug and its dosage changes with age. It is therefore important for geriatric practitioners to prescribe appropriate dosages in accordance with each senior patient's specific history and current reaction to different drugs.

There is also a difference in the metabolic rates of elderly patients of different sexes; the metabolic rate of an elderly female tends to be lower than that of an elderly male (O'Malley, Crooks, Duke, & Stevenson, 1971). Diet is another important factor. The diet of the geriatric population often differs from that of younger individuals due to reduced intestinal functioning along with chronic conditions such as high blood pressure, diabetes, and high cholesterol, all of which restrict the types of food the elderly can safely consume.

With age, the entire process of pharmacokinetics — what happens to medicinal drugs after they are ingested — evolves considerably. As age increases, intestinal function slows. Blood flow to the intestines is reduced, intestinal cells display decreased capacity for drug absorption, intestinal fluid secretion declines, and it takes a greater amount of time for a compound to pass through the intestinal tract (Aschenbrenner & Venable, 2009). There is also a decline in the secretion of the mucus lining the intestinal walls, which contains enzymes that catalyze and facilitate drug absorption. As a result, absorption of drugs into the bloodstream is slower and more prolonged in an elderly person than in a young, healthy one.

The distribution of a drug — meaning its absorption into the tissues and cells of the body — begins after it has been absorbed into the bloodstream via the intestines. This process is affected by the composition of various body fluids and tissues and how these change with age. Blood composition is heavily influenced by the protein plasma. Alterations, specifically shrinkage, in plasma levels with age can significantly influence the movement of drugs through intercellular spaces into body tissues and organs. Since aging leads to muscle loss, less fatty tissue is available for fat-soluble drugs to diffuse through. There is also a drop in total body water content, leading to lower distribution of water-soluble drugs into organs and tissues. It is therefore necessary to adjust drug dosages accordingly to prevent high levels of insoluble drug particles from accumulating in the bloodstream, which may lead to severely adverse effects. Research has shown that in elderly individuals there is something of a "brain barrier" effect, whereby drugs are delivered to the brain in higher concentrations (Alavijeh, Chishty, Qaisar, & Palmer, 2005). Hence, normal drug dosages often need to be lowered in very elderly patients.

The organs playing a fundamental role in drug metabolism are the kidneys and the liver, as they determine how long drugs remain in circulation. Because blood circulation is generally lower in the elderly, renal and hepatic blood flow is reduced compared to younger individuals. The senior population tends to have restricted liver function due to decreased liver mass caused by aging. As age increases, the liver's capacity to eliminate drug toxicity diminishes. Reduced hepatic blood flow results in reduced metabolic activity, meaning that reactions such as dealkylation, hydrolysis, hydroxylation, and nitro reduction are all less efficient. The cytochrome enzymes responsible for catalyzing drugs also decrease in content with age (George, Byth, & Farrell, 1990). As a result, unwanted medication residue can build up in the liver, leading to side effects that may be damaging to the patient's health. Dosages of medications metabolized by the liver must therefore be lowered to prevent unnecessary residue accumulation. The effect of specific drugs on cytochrome enzyme activity must also be considered: some drugs induce or inhibit these enzymes, which is of particular importance in patients prescribed multiple medications.

The kidneys, like the liver, decrease in size with age. Consequently, there are fewer functioning nephrons in the renal cavity, resulting in a lower glomerular filtration rate. Renal function is further diminished by reduced blood circulation. It has been established that after the age of 40, kidney function declines at a rate of approximately 1% per year (Sarnak et al., 2009). In the elderly, the kidneys are thus less effective at eliminating residual drugs from the bloodstream. Kidney infections and diseases common in the elderly may further hinder proper drug excretion. A reduction in drug dosage is again recommended to compensate for this diminished renal clearance.

One of the most commonly used drug categories in the elderly population is analgesics — medications known as painkillers that function to relieve pain rather than eliminating sensation entirely. As the human body ages and functions less efficiently, painful conditions become increasingly prevalent in older people. Various analgesic drugs, both prescription and over-the-counter, are widely available to treat numerous types of pain.

One prescription analgesic is Ultram (generic name: Tramadol Hydrochloride). Its primary purpose is to treat mild to severe chronic pain, including back pain and joint pain. Ultram has been used effectively in the treatment of fibromyalgia, rheumatoid arthritis, and restless legs syndrome. Although its exact mechanism of action is not completely understood, it is believed to work through two complementary mechanisms: weak inhibition of norepinephrine and serotonin reuptake (which helps increase blood flow to skeletal muscle and triggers the release of glucose from energy stores) and acting as a mu-opioid receptor agonist (which decreases pain perception and increases pain tolerance).

Another prescribed analgesic used by the elderly is Celebrex (generic name: Celecoxib), manufactured by Pfizer and available in capsule form. It is used for pain relief in rheumatoid arthritis, osteoarthritis, painful menstruation, and acute pain. Celebrex is a non-steroidal anti-inflammatory drug (NSAID) that acts as a selective inhibitor of the COX-2 (cyclooxygenase-2) enzyme, which is responsible for pain, inflammation, and the production of prostaglandins that contribute to arthritis pain.

Prescription and OTC Analgesics in Geriatric Care

A third prescription analgesic used in geriatric patients is Mobic (generic name: Meloxicam). This medication is used as an analgesic for arthritis and also has fever-reducing effects. Like Celebrex, Mobic is an NSAID. This drug class acts as both an analgesic and an antipyretic (fever reducer) and is typically used for chronic or acute pain conditions. Mobic inhibits the COX (cyclooxygenase) enzyme, which converts arachidonic acid present in cell membranes into prostaglandin. After administration, Mobic typically begins to relieve pain within 30 to 60 minutes.

Apart from prescription drugs, a number of over-the-counter medications serve as analgesics for the geriatric population. According to a survey, approximately 80% of adults in America use at least one over-the-counter drug per week, and 17 to 23% of these are analgesics (Kaufman DW, 2002).

Aspirin (chemical name: Acetylsalicylic acid) is one of the most commonly used OTC analgesics, providing relief from minor aches, pains, and headaches. It is also used in the treatment of joint pain symptoms associated with acute rheumatic fever. Aspirin works by suppressing the production of prostaglandins and thromboxane through irreversible deactivation of the cyclooxygenase enzyme.

Ibuprofen is another widely used OTC NSAID, serving primarily as a pain reliever, fever reducer, and anti-inflammatory agent. It is considered a core medicine by the World Health Organization (WHO) and is included in the WHO's Model List of Essential Medicines (Stuart MC, 2009). Like other NSAIDs, Ibuprofen works by inhibiting the COX enzyme to suppress prostaglandin production.

Naproxen is one more OTC analgesic available in the United States, where the FDA approved its over-the-counter use in 1994 (although it remains a prescription drug in most other countries). It is used to relieve pain and stiffness caused by migraines, osteoarthritis, kidney stones, tendinitis, rheumatoid arthritis, and menstrual cramps, and is also used in the treatment of primary dysmenorrhoea. Naproxen is also an NSAID and is believed to function as a prostaglandin synthetase inhibitor, though its precise mechanism of action is not fully established.

While medicines and drugs are available to act as painkillers, various alternative or complementary therapies exist for older patients to reduce medicinal intake and relieve pain through physical approaches. One of these is acupuncture, a well-known technique for pain relief originating in China over 3,000 years ago and now practiced around the globe. Researchers have found that acupuncture can provide relief from chronic back and neck pain, headaches, and osteoarthritis without the use of medications. Acupuncture is performed by inserting needles at various pressure points — commonly referred to as acupoints — of the human body. One mechanism of action involves stimulating the production of natural opioid substances in the body; needling increases the production of naturally occurring opiate compounds that act as blockers of musculoskeletal pain. Acupuncture is also known to induce relaxation in myofibrils within tissue planes, resulting in a reduction of myofibrillar entanglement.

Chiropractic care is another form of alternative therapy used to achieve pain relief. This treatment is primarily applied in the manual therapy of musculoskeletal conditions such as lower back pain, which is common in the geriatric population. It works through spinal manipulation, producing an immediate decrease in lower spine stiffness and improving the recruitment of the lumbar multifidus muscle to reduce pain.

Massage therapy is one more widely practiced form of pain relief with a long global history. This therapy is used to relax the body, relieve pain, and increase blood circulation through rubbing and the application of pressure on the body. Massage therapy can effectively relieve and loosen sore muscles, ultimately resulting in a reduction of pain.