A Practical Approach to Using Adjuvant Analgesics in Older Adults

Russell K. Portenoy, MD

Disclosures

J Am Geriatr Soc. 2020;68(4):691-698. 

In This Article

Abstract and Introduction

Abstract

The adjuvant analgesics are a large and diverse group of drugs that were developed for primary indications other than pain and are potentially useful analgesics for one or more painful conditions. The "adjuvant" designation reflects their early use as opioid co-analgesics for cancer pain. During the past 3 decades, their role in pain management has changed with the advent of many new entities, emerging data from numerous analgesic trials, and growing clinical experience. Many of these drugs are now used as primary analgesics for specific types of chronic pain. With proper patient selection and cautious administration, they can potentially contribute meaningfully to the management of chronic pain in older adults. A practical approach categorizes the many adjuvant analgesics by broad indications: multipurpose drugs and drugs that target neuropathic pain, musculoskeletal pain, and cancer pain, respectively. This article reviews the status of the evidence supporting the analgesic potential of the adjuvant analgesics and discusses best practices in terms of drug selection and dosing.

Introduction

Use of the term "adjuvant analgesic" became commonplace after the World Health Organization published an influential guideline on the management of cancer pain in 1986.[1] This guideline recommended selected corticosteroids, anticonvulsants, and psychotropics as co-analgesics when opioid therapy proved inadequate. They were therefore considered adjuvant therapy intended to boost opioid effectiveness, provide an opioid-sparing effect, or offer a means to target a specific type of pain.

Practice Pointers
• Adjuvant analgesics are drugs developed for other indications that may be useful for chronic pain. Older patients with chronic pain should be assessed to determine whether any of the multipurpose adjuvant analgesics, or any of those drugs used selectively for neuropathic pain, musculoskeletal pain, or cancer pain, should be recommended.
• Most adjuvant analgesics are centrally acting and must be used cautiously in older adults. Irrespective of the drug, treatment should be initiated at a low dose, and dose titration should involve small increments at intervals adequate to monitor response. Ineffective drugs should be discontinued.
• Multipurpose adjuvant analgesics may be considered for any type of chronic pain. Preferred analgesic antidepressants include the serotonin-norepinephrine reuptake inhibitors, particularly duloxetine, and the secondary amine tricyclic drugs desipramine and nortriptyline. Topical analgesics should be considered whenever pain is focal or regional.
• For neuropathic pain, the preferred approach involves treatment with an analgesic antidepressant or a gabapentinoid and concurrent use of a topical agent if appropriate.
• Musculoskeletal pain disorders may be addressed with several of the multipurpose adjuvant analgesics, such as the antidepressants and tizanidine, and topical agents. The socalled muscle relaxants are not preferred for chronic pain.
• Adjuvant analgesics may be useful in opioid-refractory cancer pain syndromes. Bone pain is commonly treated with osteoclast inhibitors, and pain related to bowel obstruction may be addressed by a combination of drugs including a glucocorticoid and antisecretory drugs.

In the ensuing decades, the meaning of "adjuvant analgesic" evolved in tandem with emerging evidence from trials of new or existing drugs in varied types of chronic pain. The term now refers to a large and diverse group of drugs that were originally developed for primary indications other than pain but have the potential for analgesic efficacy in one or more painful conditions. The "adjuvant" label is now a misnomer. Although these drugs can be combined with primary analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs), or opioids, as co-analgesics, this is no longer a defining feature.

In older adults, chronic pain is both highly prevalent and consequential, and analgesic pharmacotherapy is commonly offered, notwithstanding the risks associated with the primary systemic analgesics.[2] NSAIDs, for example, may result in life-threatening gastrointestinal hemorrhage or acute kidney injury; opioids are subject to abuse and may result in cognitive impairment, falls, or unintended overdose. Although age- and disease-associated changes in pharmacokinetics and pharmacodynamics, risk of adverse effects such as cognitive impairment and falls, and the potential for drug-drug interactions related to polypharmacy[3–7] necessitate a cautious approach when the adjuvant analgesics are used in older patients, they nonetheless offer numerous therapeutic options when primary analgesics are ineffective or not preferred (Table 1).

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