Drug-drug interaction between diclofenac, cetirizine and ranitidine.

The interactions between diclofenac (1), cetirizine (2) and ranitidine (3) were investigated by thermal analyses and UV, IR and (1)H NMR spectroscopic studies. In aqueous solution interaction occurred only between 1 and 2, yielding a high molecular weight (1:1), water insoluble ionic salt. Weak charge transfer (CT) interaction exists between the doubly charged piperazine moiety in 2, acting as an electron acceptor and (1). This CT interaction originates from the aromatic groups in 1. The CT band observed at approximately 315 nm exhibits very low absorbance as a result of the partial neutralization of the two positive charges present in the ionic salt. The IR bands of the mixture have wave numbers at nu 3323.1, 1695.3, and delta 1321.1-1210 cm(-1) indicating the presence of the NH group and the neutralized carbonyl group of 1, as well as the carboxylic group of 2. The 1,2,3-substitutions in the benzene ring of 1 in the mixture appear at 1161.1 cm(-1). The (1)H NMR of the mixed drugs shows singlet, triplet and multiplet proton signals due to the same effect.