CHAPTER 14: Opioid Analgesics

INTRODUCTION

Analgesic drug therapy and certain rehabilitation interventions share a common goal: pain relief. Consequently, analgesics are among the drugs most frequently taken by patients who are treated in a rehabilitation setting. The vast array of drugs that are used to treat pain can be roughly divided into two categories: opioid and nonopioid analgesics. Nonopioid analgesics are composed of drugs such as acetaminophen, aspirin, ibuprofen, and similar agents. These drugs are discussed in Chapter 15.

Opioid analgesics are a group of naturally occurring, semisynthetic, and synthetic agents that are characterized by their ability to relieve moderate-to-severe pain. These drugs exert their effects by binding to specific neuronal receptors that are located primarily in the central nervous system (CNS). Opioid analgesics are also characterized by their potential ability to produce physical dependence and are classified as controlled substances in the United States because of their potential for abuse (see Chapter 1 for a description of controlled substance classification). Morphine is considered the prototypical opioid analgesic, and other drugs of this type are often compared to morphine in terms of efficacy and potency (Fig. 14-1).¹

In the past, the term narcotic was often applied to these compounds because when taken, they tend to have sedative or sleep-inducing side effects, and high doses can produce a state of unresponsiveness and stupor. However, narcotic is a misleading name, because it describes a side effect rather than the principal therapeutic effect.

Likewise, these drugs are frequently referred to as opiate analgesics because some of these compounds are derived from opium. More recently, the term opioid has also been instituted to represent all types of narcotic analgesiclike agents, regardless of their origin.² Consequently, most sources preferentially use the term opioid to describe these drugs, and clinicians should recognize that this term represents all of the morphinelike medications.

You will frequently encounter patients taking opioids for acute pain after surgery and trauma and for more long-term conditions such as chronic severe musculoskeletal pain. These drugs are also a mainstay in reducing pain and improving quality of life in patients with advanced cancer. Opioids are often very helpful in reducing pain and in helping the patient be more active and engaged in exercise and other rehabilitation interventions. But these drugs are notorious for producing serious side effects, and their addictive potential often raises concerns in patients and medical practitioners. Hence, this chapter will introduce you to the actions and beneficial effects of opioid analgesics, their potential side effects, and how these drugs can have positive and negative effects on physical rehabilitation.

SOURCES OF OPIOID ANALGESICS

As mentioned previously, opioid analgesics can be obtained from natural, synthetic, or semisynthetic sources. Synthetic agents, as the designation implies, are simply ...