Introduction

The term adjuvant analgesic was originally coined to refer to a small number of drugs that were commercialized for reasons other than pain but could be used as analgesics in selected circumstances. When these nontraditional analgesics were prescribed to cancer patients to supplement the analgesia provided by opioids, they were considered to be adjuvant to the mainstay therapy – hence the term. In recent years, the number, diversity, and conventional use of these nontraditional analgesics have increased dramatically. Several are now indicated and promoted for specific types of noncancer pain and many are used as first-line therapies in varied populations. Accordingly, the term adjuvant analgesic is now a commonly applied misnomer and refers to a large and diverse group of drugs that have an expanding role in pain medicine.

In the management of cancer pain, the term adjuvant analgesic also must be distinguished from other labels, specifically adjuvant drug and co-analgesic. According to the three-step analgesic ladder model of cancer pain pharmacotherapy developed under the auspices of the World Health Organization in the mid-1980s, adjuvant drugs comprise both analgesics used to supplement opioid therapy (adjuvant analgesics) and drugs used to manage the side effects of the opioids. Given this dual labeling, the drugs intended to provide analgesia are best denoted by the more specific term adjuvant analgesics. The label co-analgesic has been used synonymously with adjuvant analgesic in the cancer treatment setting and also could be used whenever referring to a drug added for analgesic purposes to an existing opioid regimen.