Drug Delivery Mechanism of Sulfathiazole from Polyurethane Films

Urinary and cardiac catheters, made of polyurethane, are used in patients for extended periods of time. As a result of a catheter’s location and prolonged use, the catheter is vulnerable to contaminants that lead to infections by microorganisms such as Escherichia coli and Candida spp. A polymer that can prevent the development of these microbes, without compromising the functionality of the catheter, would be an ideal solution to this problem. The purpose of this experiment is to develop a polymer that contains an antimicrobial commonly used to treat the various causes of catheter-induced infections.

Polyurethane is the preferred material for catheter production due to its biocompatibility with patients, and, thus, became the material of choice for trials. Sulfathiazole, similarly, has a history of being prescribed for various infections, including urinary tract infections. Sulfathiazole also has the added benefit of being soluble in water, an important factor for testing the concentration of drug releasing from the polyurethane during testing.

Sample films were made by solvent casting. Sulfathiazole and polyurethane were dissolved in a solution of dimethylformamide and tetrahydrofuran. The resultant solution was constantly stirred for 24 hours, after which it was poured into molds, and the molds were placed in an oven at 37°C for 24 hours. The dried films were released from the molds and stored in a desiccator. In order to confirm that sulfathiazole can diffuse out of the polyurethane, a precisely weighed portion of the drug-loaded polymer film was immersed in distilled water constanly stirred at 200 RPM and 37°C for 24 hours. Every hour, 5 mL aliquot was taken out and tested with a Shimazdu UV-2450 spectrometer to measure the absorbance at 270 nm. The concentrations of aliquotes taken out periodically were calculated from the absorbance values and the calibration curve made with standard aqeous solutions of sulfathiazole with different concentrations, ranging from 0.5 µg/mL to 5 µg/mL

Drug-loaded polymer films were made with two different sulfathiazole concentrations, 0.3 wt/wt% and 1.5 wt/wt%. Both concentrations show similar release mechanisms which follow the Korsemeyer-Peppas kinetic model of diffusion. From the similarity in release rates and kinetic modeling, it can be concluded that the diffusion behavior of sulfathiazole is independent of its concentration. The most important conclusion is that the sulfathiazole is capable of diffusing out of polyurethane at a dependable rate.