Pharmacotherapy of opioids: present and future developments.

The clinically available opioids have different physicochemical properties, resulting in differences in clinical profile with regard to potency, onset, and duration of activity. However, they all have comparable side-effects after acute systemic application. Several approaches can be used to overcome these side-effects. The following approaches, with special emphasis on the perioperative use of the opioids, are discussed: (1) the use of alternative routes of administration, such as via the spine (epidurally and intrathecally); (2) optimization of opioid delivery by means of slow-release preparations, chronic infusions with indwelling catheters, and transdermal delivery systems; (3) use of additional agents to potentiate the analgesic properties of the opioids so that the dose of opioid can be reduced; and (4) searching for new analgesics on the basis of knowledge of the pain-transmission system and the different opioid receptors with their functional interactions.