Polylactide (PLA) microspheres were prepared using the solid-in-oil (S/O) spray-drying method to achieve the sustained release\nof a hydrophilic drug for the treatment of tuberculosis, via intratracheal instillation. Isoniazid (IN), a\nlow-molecular-weight hydrophilic drug, was used as a model drug. The effects of various sizes of micronized IN powder, different\ndrug/polymer ratios, spray-drying process parameters, and drug-release characteristics were studied to optimize the\nmanufacturing parameters. A high entrapment efficiency (87.3%) was obtained using this method; furthermore, the microspheres\nwere spherical and smooth. They were individually and homogenously distributed, with a mean diameter of 5.6 m;\nfurthermore, they showed a satisfactory extended sustained-release phase. After administration of the microspheres to rats,\npulmonary drug concentrations were maintained at a relatively stable level for up to 4 weeks.
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