| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 600217 | Colloids and Surfaces B: Biointerfaces | 2013 | 8 Pages |
Indomethacin (IM) easily forms an amorphous complex with lidocaine (LC) by heat treatment. To know the mechanism involved in the formation of this complex, we studied temperature-dependent phase changes in mixtures of IM and lidocaine hydrochloride (LH), in which the cationic form of LC forms a salt with Cl−, in various molar ratios by using DSC and NMR. Although heating of the mixture of IM and LC (IM + LC), formed a eutectic mixture, that of IM and LH (IM + LH) did not, and IM in the IM + LH mixture was dissolved into fused LH. Cooling of the fused IM + LH showed the glass transition in all of the samples containing various amounts of IM, suggesting that fused IM + LH took a homogenous amorphous state (IM/LH) below its glass transition temperature, in contrast to the fused IM + LC, which formed the rubber state and/or glass state depending on the molar content of IM. The results of the NMR study showed that IM in IM/LH caused the electronic structure of LH to change in such a way as to become similar to that of LC, but this effect was limited. Hence, mode of interaction of LH with IM is different from that of LC with IM.
Graphical abstract.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Heat-treatment of lidocaine HCl forms an amorphous state. ► Indomethacin is dissolved into fused lidocaine HCl by heating of their mixture. ► Indomethacin and lidocaine HCl form an amorphous mixture. ► Their mixtures show a glass transition on cooling. ► Indomethacin changes electronic structure of lidocaine HCl to that of lidocaine.
