Pain Management in the Elderly: Focus on Safe Prescribing
In 2015, the number of people in the United States age 65 or older reached 47.8 million.1 As we have been reporting in Practical Pain Management, the prevalence of chronic pain among the elderly is a growing concern.2,3 A recent study found that 52.3% of patients age 65 and older reported having bothersome pain in the last month; three-quarters of them reported having pain in more than 1 location.4
Due to the greater presence of multiple comorbidities in the elderly, which often necessitates polypharmacy, there is an increased risk of adverse events (AEs) when these patients take analgesic medications. This article will examine the most commonly used pain management therapies, outlining their pharmacokinetic and safety profiles in the elderly population.
Problems Associated With Medical Pain Management in the Elderly
Aging is the physiologic process of degeneration, resulting in the deterioration of cellular structure and organ system failure.5 Select organ systems that are particularly important when initiating and dosing analgesics include the gastrointestinal (GI), hepatic, renal, cardiovascular, and respiratory systems. The physiologic changes that occur with aging have important pharmacokinetic implications, which may translate into increased risks for AEs and drug-drug interactions and present significant challenges to clinicians trying to provide appropriate pharmacotherapeutic regimens.
There are a multitude of age-related pharmacokinetic changes clinicians should consider before selecting therapies. Decreases in gastric secretion and intestinal motility lead to decreased absorption of specific nutrients and altered absorption of certain drugs.6,7 The aging adult may have increases in body fat and decreases in lean body mass, total body water, and serum albumin that may impact the distribution of medications.8 Circulating albumin and other proteins, such as alpha-glycoprotein, bind many different analgesic drugs, the most common examples being nonsteroidal anti-inflammatory drugs (NSAIDs) and tricyclic antidepressants (TCAs). This becomes an important issue if more unbound drug becomes available for activity, toxicity, and drug-drug interactions in older patients compared with younger patients with adequate circulating proteins. Various changes can increase the volume of distribution and half-life of lipophilic drugs, while increasing plasma concentrations of hydrophilic and highly protein-bound acidic drugs.8
Changes in hepatic and renal function that occur in the elderly population can affect drug metabolism and elimination. Hepatic volume and hepatic blood flow both decline with age.6,8,9 Although the clinical impact that normal aging has on overall drug metabolism remains controversial, it is generally accepted that there are slight reductions in phase I metabolism and little to no reductions in phase II metabolism.6,8,9 However, concurrent cirrhosis, chronic liver disease, or chronic kidney disease all have been shown to impact drug metabolism to a greater extent.6-9 Similarly, aging is associated with progressive nephrosclerosis and decreased renal blood flow, resulting in an overall decreased glomerular filtration rate that may subsequently cause increased serum concentrations of renally cleared drugs and their metabolites.8,10 The decline in both hepatic and renal function may lead to an increased propensity toward AEs and drug-drug interactions due to elevated parent drug/metabolite concentrations.
Although all the above characteristics can lead to unintended accumulation of parent drugs and their metabolites, other processes of aging also may increase risk due to their interactions with the mechanisms of the therapies themselves. One example is changes in cardiovascular health, such as hardening of elastic arteries, enhanced pulse wave velocity, and prolonged ejection fraction, all of which increase blood pressure, left ventricular hypertrophy, and cardiac risk.5,11 The GI changes cited above also may increase the prevalence of constipation in this population.6,7 Decreases in the elasticity of the lung and increased chest wall rigidity inevitably lead to reductions in respiratory ability, which increases the risk of respiratory depression.5 Finally, this population is at increased risk of falls and is much more susceptible to the cognitive and sedative effects elicited by many pain management medications.
Although there are well-founded guidelines and several published review articles to assist with treatment selection, physicians still have reservations when managing pain in this population. Therefore, clinicians must take a patient-centered approach to pain management. They should view each elderly patient as an individual, accounting for comorbid disease states and pharmacokinetic and safety profiles to promote selection of the safest and most efficacious pain management therapy.
Current Geriatric Pain Management Recommendations
In 2009, the American Geriatric Society (AGS) published evidence-based guidelines for treating pain in the elderly.12 The AGS guidelines recommend acetaminophen as the initial (first-step) and ongoing pharmacotherapy for pain management; opioids are recommended for the treatment of moderate-to-severe pain, and adjunctive analgesics are to be used for patients with specific pain types, such as neuropathic pain. The guidelines recommend that analgesics such as NSAIDs, corticosteroids, and TCAs be avoided due to their potential to cause AEs and worsen certain disease states.
In general, clinicians accept that mild pain can be managed by non-pharmacologic therapy such as heat or ice, massage, and other non-medication modalities; moderate pain can be treated with all of these modalities plus over-the-counter (OTC) medications and/or nonopioids; and that severe pain may require intermittent or regular use of opioids. Consistent with AGS guidelines, pharmacological management of persistent pain is warranted in this population if pain “affects physical function or quality of life.”12