Clinical Pharmacology of the Opioid Analgesics

CLINICAL PHARMACOLOGY OF THE OPIOID ANALGESICS

Successful treatment of pain is a challenging task that begins with careful attempts to assess the source and magnitude of the pain. The amount of pain experienced by the patient is often measured by means of a pain Numeric Rating Scale (NRS) or less frequently by marking a line on a Visual Analog Scale (VAS) with word descriptors ranging from no pain (0) to excruciating pain (10). In either case, values indicate the magnitude of pain as: mild (1–3), moderate (4–6), or severe (7–10). A similar scale can be used with children and with patients who cannot speak; this scale depicts five faces ranging from smiling (no pain) to crying (maximum pain).

For a patient in severe pain, the administration of an opioid analgesic is usually considered a primary part of the overall man-agement plan. Determining the route of administration (oral, parenteral, neuraxial), duration of drug action, ceiling effect (maximal intrinsic activity), duration of therapy, potential for adverse effects, and the patient’s past experience with opioids all should be addressed. One of the principal errors made by physi-cians in this setting is failure to adequately assess a patient’s pain and to match its severity with an appropriate level of therapy. Just as important is the principle that following delivery of the thera-peutic plan, its effectiveness must be reevaluated and the plan modified, if necessary, if the response was excessive or inadequate.

Use of opioid drugs in acute situations may be contrasted with their use in chronic pain management, in which a multitude of other factors must be considered, including the development of tolerance to and physical dependence on opioid analgesics.