Molecular complex consisting of two typical external medicines: Intermolecular interaction between indomethacin and lidocaine

Abstract

The molecular complex formed between indomethacin (IDM) and lidocaine (LDC), which are typical external medicines, was studied. A thermal analysis, microscopic study and phase solubility technique suggested intermolecular interaction between IDM and LDC. The phase solubility profiles with IDM and LDC were classified as AL-type, indicating the formation of a 1 : 1 stoichiometric molecular complex. The apparent stability constant (K S), calculated from the slope and the intercept, was 4478.9M -1. A molecular ion peak was detected at 592.2 (m/z) from fast-atom bombardment-MS measurements, which was in accordance with the sum of the molecular weight for IDM (MW: 357.81) and LDC (MW: 234.38). The changes of IR spectra in the C=O stretching region showed that each intact hydrogen bond network was collapsed in the IDM-LDC system and strong interaction between IDM and LDC formed after their kneading. From the 1H-NMR analyses, it was estimated that the dominant interactive site was the IDM carboxylic acid group which associated with the LDC diethyl amino group non-covalently. © 2007 Pharmaceutical Society of Japan.