Effect of different ratios of high and low molecular weight PLGA blend on the characteristics of pentamidine microcapsules

• Published in: International journal of pharmaceutics 2004-02, Vol.270 (1), p.251-262
• Main Authors: Graves, Richard A, Pamujula, Sarala, Moiseyev, Raisa, Freeman, Thomas, Bostanian, Levon A, Mandal, Tarun K
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Calorimetry, Differential Scanning; Capsules; Dissolution; Drug Carriers; Drug Stability; Formulation; General pharmacology; Glycolates - chemistry; Lactic Acid; Medical sciences; Microcapsules; Molecular Weight; Particle Size; Pentamidine; Pentamidine - administration & dosage; Pentamidine - chemistry; Pharmaceutical technology. Pharmaceutical industry; Pharmacology. Drug treatments; PLGA; poly(lactide-co-glycolide); Polyglycolic Acid; Polylactic Acid-Polyglycolic Acid Copolymer; Solubility; Solvent evaporation; Time Factors; Viscosity
• ISSN: 0378-5173; 1873-3476
• DOI: 10.1016/j.ijpharm.2003.10.019

Two different PLGA samples (Resomer 502 and Resomer 506), either alone or in combinations, were used to prepare microcapsules. Microcapsules were prepared using a double emulsion solvent evaporation technique. The efficiency of encapsulation increased significantly when a mixture of 1 part Resomer 506 and 7 parts Resomer 502 was used to prepare the microcapsules. The efficiency of encapsulation of this batch was 23.7%, whereas the efficiency of encapsulations was only 13.9 and 9.8%, respectively, when the microcapsules were prepared with 100% Resomer 502 or 100% Resomer 506. In contrast, irrespective of the relative ratio of Resomer 502/Resomer 506, the median particle size of the microcapsules showed similar distribution pattern with the median size lies between 49 and 83 μm. The glass transition temperature ( T g) decreased significantly (44.6–25.5 °C) as the amount of Resomer 502 was increased in the formulation. The presence of Resomer 502 at lower concentration, along with Resomer 506, initially reduced the “burst effect.” However, incorporation of a higher amount of Resomer 502 increased the “burst effect.” Drug release from these microcapsules continued over 80 days. In conclusion, efficiency of encapsulation increased significantly when Resomer 506 was mixed with Resomer 502 at a ratio of 1:7. Blending of Resomer 502 with Resomer 506 reduced the glass transition temperature, which resulted in higher amount of drug release throughout the dissolution study.