Preparation and evaluation of eudragit gels. V. Rectal gel preparations for sustained release and avoidance of first-pass metabolism of lidocaine.

The release of lidocaine from hydrogel and xerogel preparations was remarkably suppressed compared with polyethylene glycol (PEG) 2000 suppository. The release rate of lidocaine from hydrogel and xerogel increased with the increase in the amount of sodium hydroxide incorporated within the range of 3 to 7 milliequivalent (meq). After an oral administration of lidocaine HCl solution, the plasma concentration of lidocaine was considerably lower than that after intravenous administration for all time periods. The absolute bioavailability (F(oral)) was 5.63%. For the Witepsol S-55 and PEG 2000 suppositories, the plasma levels of lidocaine were higher than those for the oral preparation, and Cmax and area under the concentration-time curve (AUC) values significantly improved (p < 0.01). The absolute bioavailabilities were 21.3 and 29.6%, respectively. On the other hand, Eudispert hv-hydrogel and xerogel preparations showed the characteristics of a sustained-release preparation, especially the xerogel preparation with 5 meq NaOH. Absolute bioavailability for hydrogel and xerogel preparations increased significantly (p < 0.05) by approximately 1.7-3.4 folds compared with those of Witepsol S-55 and PEG 2000 suppositories.