Patient-controlled analgesia. Pharmacokinetic and therapeutic considerations

The opioid analgesic agents exhibit relatively large pharmacokinetic differences between drugs, and there is substantial pharmacokinetic and pharmacodynamic variability across subjects or patients with each agent. The advent of patient-controlled analgesic administration techniques and their widespread use in contemporary pain management, especially in postsurgical and cancer patients, has decreased the unfortunate impact of interpatient variability on achieving the optimal balance between pain relief and opioid adverse effect intensity. The improvements in pain management provided by patient-controlled analgesia do not, however, decrease the importance of knowledge of opioid pharmacokinetics towards enlightened use of these drugs and attainment of maximal benefits from them in any patient. Future improvements in patient-controlled analgesia technology will probably be based on the pharmacokinetic behaviour of different opioid analgesic agents in specific receptor-containing regions. Finally, physicochemical and pharmacokinetic characteristics of these agents are important determinants of the speed of onset of effects, duration of action and spinal selectivity of epidurally and intrathecally administered analgesics. Thus, effective patient-controlled analgesia depends on an understanding of the differential pharmacokinetics of opioids self-administered by a variety of possible modes.