OPIOID ANALGESICS - COMPARATIVE FEATURES AND PRESCRIBING GUIDELINES

The term 'opioid' is a generic term for naturally occurring, semisynth etic and synthetic drugs which combine with opioid receptors to produc e physiological effects and which are stereospecifically antagonised b y naloxone. For clinical purposes, opioids can be classified according to their receptor interactions (agonist, partial agonist, agonist-ant agonist and antagonist), the pain intensity for which they are convent ionally used (moderate or severe), and their half-life (short or long) . Pure agonists conventionally used for moderate pain, short and long half-life pure agonists conventionally used for severe pain, mixed ago nist-antagonists and partial agonist opioids are described in detail. The effective clinical use of opioid drugs requires familiarity with d rug selection, routes of administration, dosage guidelines and potenti al adverse effects. Opioids are unequivocally indicated in the managem ent of severe acute pain and moderate to severe pain associated with c ancer. There is increasing acceptance of the role of opioids in the ma nagement of recurring acute pain, chronic nonmalignant pain of organic origin and severe neuropathic pain. The selection of opioids is influ enced by pain intensity, pharmacokinetic and formulary considerations, previous adverse effects and the presence of coexisting disease. Some patients will require sequential trials of several different opioids before a drug which is effective and well tolerated is identified. Opi oid agents should be administered by the most comfortable and convenie nt route that meets the specific needs of the patient. The regimen for opioid medications should generally provide around-the-clock analgesi a with provision for rescue doses for the management of exacerbations of the pain not covered by the regular dosage. At all times, uncontrol led pain should be addressed by gradual increase in the opioid dose un til either pain control is achieved or intolerable and unmanageable ad verse effects supervene. The management of pain with opioid analgesics demands frequent patient assessment and a readiness to re-evaluate th e therapeutic plan in the setting of either inadequate relief or adver se effects.