Improvement of some pharmaceutical properties of drugs by cyclodextrin complexation .7. Trimethoprim

Inclusion complexation of trimethoprim (TMP) with 3 cyclodextrins (alpha-, beta-, and gamma-CyDs) in water and solid phase were studied by the solubility method, spectroscopy (UV, IR), X-ray diffractometry, thermal analysis and their modes of interactions were assessed. A spacial relationship between host and guest molecules was clearly reflected in the magnitude of the stability constant (gamma- > beta- > alpha-CyD). The investigated cyclodextrins were found to increase the solubility of the drug in water to a marked extent. Calculating the amount of drug in free and complexed forms revealed that solubilization is totally due to complex formation. The solid complexes of TMP with alpha-, beta- and gamma-CyDs were prepared in molar ratios of 1:1 and their dissolution behavior was examined. The results indicated that the CyD complexes may have great utility as a rapidly dissolving form of TMP in water especially gamma-CyD.