Prolongation of epidural analgesia using solid lipid nanoparticles as drug carrier for lidocaine.

Abstract

Solid lipid nanoparticles (SLNs), as a drug carrier, are a very attractive strategy for sustained and controlled drug release. In this study, we investigated the feasibility of SLNs to prolong the action of lidocaine for potential application in epidural anesthesia and analgesia. Lidocaine-loaded SLNs were prepared with different lipids, including monostearin (MS), glyceryl palmitostearate (GP), and stearic acid (SA). The morphology and crystallinity were characterized with transmission electron microscopy and powder x-ray diffraction. In vitro release studies were carried in phosphate buffer solution of pH 7.4 using cellulose dialysis membrane. The in vivo efficacy of epidural anesthesia was evaluated in rats. Lidocaine was successfully incorporated in SLNs prepared with MS, GP, and SA, respectively. The particle sizes of lidocaine-loaded SLNs were 143 to 388 nm with polydispersity index of 0.29 to 0.45. Powder x-ray diffraction analysis showed that lidocaine was mainly dispersed in SLNs in an amorphous state. The in vitro release within 48 hrs showed that lidocaine released from SLNs was 80% with MS SLNs, 69% with GP SLNs, and 89% with SA SLNs. The epidural efficacy was compared with that of aqueous lidocaine HCl. Single injection of lidocaine SLN suspension produced epidural block for more than 8 hrs with MS SLNs, 12 hrs with GP SLNs, and 4 hrs with SA SLNs. ]The same dose of lidocaine in aqueous solution lasted for less than 2 hrs. Solid lipid nanoparticles can be exploited as a promising drug carrier for extending the action of lidocaine.