Development of polymeric structures for encapsulation of hydrophilic/ hydrophobic drugs

Bioavailability of drugs is of utmost importance to achieve the desired therapeutic effects of them. The solubility of a drug is the fundamental determinant of its bioavailability. The aim of this thesis was to slow down the dissolution rate of metformin, a hydrophilic drug and to increase the solubility and dissolution rate of karvedilol, a hydrophobic drug. To achieve this goal, selected drugs were encapsulated using different types of polymers, copolymers, and polymer blends through the nano-precipitation method. The structural characterization of the obtained encapsulated particles was performed using Fourier-transform infrared (FTIR) spectroscopy. In addition, differential scanning calorimetry (DSC) analysis was carried out for the products encapsulating karvedilol. The results demonstrated that karvedilol, in its low solubility crystal form, was transformed into an amorphous state through encapsulation. The particle structures were examined using microscopy, and the particle sizes were measured using a zetasizer. The drug release rates from the obtained encapsulated particles were determined. Ethyl cellulose, hydroxypropyl cellulose, poly(lactide-co-glycolide) (PLGA), ammonioethyl methacrylate-methyl methacrylate copolymer, neutral ethyl acrylate-methyl methacrylate copolymer, and their blends were used for encapsulation. The effects of the molecular weight of the polymers, drug-to-polymer ratio, mixing rate, and surfactant type used on the obtained encapsulated drug particles were investigated. The particles were obtained with high encapsulation efficiency in the range of 200-300 nm. Encapsulation of metformin using a triple polymer blend, which is not reported in the literature, resulted in particle size, encapsulation efficiency, and dissolution rate that suggest it could be a promising product for cancer preventive therapies. Encapsulation of karvedilol with PLGAs having different lactide glycolide ratios resulted in higher encapsulation efficiency than the existing literature and significantly increased the solubility of karvedilol, making it a promising candidate for extended-release formulations for hypertension treatment.