Polyurethanes loaded with antibiotics: influence of polymer-antibiotic interactions on in vitro activity against Staphylococcus epidermidis.

Acidic or basic polyurethanes were loaded with antibiotics to develop materials to prevent medical device-related infections. A correlation between polymer-antibiotic interactions and amount of drug absorbed by polymers and released over time was found. Since the employed antibiotics, i.e. amoxicillin, cefamandole nafate, rifampin and vancomycin, possessed at least an acidic group in their structural formula, the introduction of basic tertiary amines in the polyurethane side-chain resulted in an increased polymer ability to adsorb antibiotics. However, a stronger ionic interaction between this polymer and the antibiotics caused a release of lower amount of drug over time. Antibiotics released from polymers inhibited Staphylococcus epidermidis growth on agar. Antibiotic-loaded polyurethanes kept in water for increasing times were still able to show inhibition zones of bacterial growth. The antibacterial activity lasted up to 3 hours for amoxicillin, 24 hours for vancomycin, 8 days for cefamandole nafate and 8 months for rifampin.