Preparation and evaluation in vitro and in vivo of polylactic acid microspheres containing dibucaine.

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Abstract
DL-Polylactic acid microspheres containing dibucaine were prepared, and release patterns of dibucaine from the microspheres as well as the local anesthetic effects of the drug in the microspheres were examined. The influences of nonsolvents and dibucaine concentration at preparation on the characteristics and dibucaine contents of the microspheres were investigated. Higher pH in nonsolvents and higher dibucaine concentration at preparation resulted in increased dibucaine contents in the microspheres. The release patterns of dibucaine from microspheres varied significantly among microspheres with different dibucaine contents, and the release mechanisms of dibucaine from microspheres were greatly influenced by disintegration of the microspheres. The local anesthetic effects of 0.1 ml aliquots of dibucaine hydrochloride solutions were examined at 4 concentrations in vivo in guinea pigs. The local anesthetic effects of dibucaine in microspheres were compared with those of the above solutions in relation to the release rate of dibucaine from microspheres in vitro. The more the amount of dibucaine, the stronger was the local anesthetic effect. The local anesthetic effect of dibucaine in microspheres lasted much longer (300 h) than that of dibucaine hydrochloride solutions. The profile of local anesthetic effect of dibucaine in microspheres in vivo was different from the release profile in vitro.