Prospects for Future Development
Despite the fact that the synthetic opioids have a wide therapeutic margin of safety and induce a negligible impairment of the cardiovascular system, respiratory depression and dependence liability are still the foremost undesirable side effects. Selective antagonists are able to reserve the drawback of a respiratory function impairment. As their use is bound to cardiovascular stimulating effects and because of their short duration of action after a single injection, it is difficult to prevent an opioid-induced late respiratory depression. Attention, therefore, is now focused on new groups of opioids, derivatives of benzomorphanes which advantageously interact selectively with the so-called kappa-receptors and are remarkable in not causing respiratory depression. This class of opioids has shown potential for wide use in anaesthesiology. It remains to be seen, however, whether the dysphoric component, often observed after the administration of pure kappa-ligands, can be eliminated so that their use in the clinic may be considered.