Hydroxypropyl-beta-cyclodextrin can modulate the activity of spinally administered sufentanil

Hydroxypropyl-beta-cyclodextrin increased the effectiveness of sufentanil after epidural and intrathecal administration in rats, both in terms of a longer duration of analgesia after a fixed dose of sufentanil, and in a reduction of the lowest ED50s to produce analgesia. There was also an increase in specificity, as indicated by the greater dissociation between the ED50s for analgesia and for supra-spinal side-effects. Maximal activity was measured after inclusion complexation of sufentanil in 10% hydroxypropyl-beta-cyclodextrin. At higher concentrations of hydroxypropyl-beta-cyclodextrin, both the activity and the specificity were attenuated. The increased safety of sufentanil in 10% hydroxypropyl-beta-cyclodextrin after spinal administration was also confirmed in terms of opioid-induced deviations in arterial PO2, PCO2 and oxygen saturation. At a dose of twice the ED50 for deep surgical analgesia, the sufentanil/hydroxypropyl-beta-cyclodextrin complex produced no changes in these parameters. With sufentanil alone at comparable analgesic doses, significant shifts in all three parameters were present immediately after drug administration. At higher concentrations of sufentanil in hydroxypropyl-beta-cyclodextrin changes in the three blood gases were present but the deviations were always smaller than those observed with comparable doses of plain sufentanil. These results support the notion that after complexation sufentanil is present longer at the spinal level after spinal administration. As a consequence, there is less free sufentanil available for redistribution into lipid tissue and into the circulatory system, producing less systemic side-effects.