Formation constants of combinations resulted from the interactions of active with auxiliary substances are important characteristics for the formulation of new drugs especially of those with controlled and targeted delivery. Povidone, a synthetic macromolecular excipient, is frequently used in the preparation of dosage forms. Because of its similar structure to proteins, povidone may form complex combinations with partners of reaction. Complexation of the active substance modifies the biodisponibility and the pharmacokinetics of the pharmacon. In the present study we have followed the interaction of povidone with antibiotics - ampicilline, streptomycine, tetracycline, doxycycline - by potentiometric measurements. The combining molar ratios of the resulted complexes were 1:1 and 2:1 respectively, and the magnitude of the formation constants varied between 103 – 106, in the 5 to 9 pH interval. The interactions took place via hydrogen bonds and van der Waals forces.
Keywords: polyviniypyrrolidone, amynoglycoside- and tetracycline-type antibiotic, phsyico-chemical interactions