This chapter is not intended to be a comprehensive pharmacopoeial treatment of opioid pharmacology; rather, its purpose is to emphasize principles using the main opioid analgesics in current clinical practice as examples.

Overview of the Use of Opioid Analgesics

Opioid analgesics are first-line medication for moderate to severe nociceptive pain. Their clinical effectiveness in this role is traditional and unquestioned. They are highly effective, inexpensive, and relatively simple to use. In addition, they may produce a sense of well-being, and, by control over pain, they promote restful sleep. Nevertheless, the results of most surveys indicate that pain management is suboptimal (Bruster et al., 1994; Zhukowsky et al., 1995). When current analgesic medications can be so effective, why is pain management not always excellent? There are many reasons. Although attitudes, teaching, and unfavorable logistics among medical and nursing staff may contribute, perhaps compounded by vagaries associated with inappropriate dosage regimens, fickle routes of administration, and unfavorable individual pharmacokinetics, the drugs themselves are not blameless. Opioid analgesics have a spectrum of side effects that can limit their usefulness, so that some patients may even prefer to endure pain than to withstand the side effects of the therapy.

Development of new agents over the past decades has never significantly dissociated the adverse from the salutary actions of opioid analgesics. The deficiencies of opioid analgesics include their potential for initiating drug dependence; life-threatening ventilatory depression; untoward central nervous system (CNS) responses such as somnolence, excitation, and dysphoria; and gastrointestinal disturbances, particularly nausea, emesis, gastroparesis, and constipation; and for generating a miscellany of lesser studied effects such as pruritus, altered immunocompetence, and impaired micturition.