Solid lipid microparticles for the stability enhancement of the polar drug N6-cyclopentyladenosine

The objective of this study was to prepare solid lipid microparticles (SLMs) loaded with the polar adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA). The microparticles were produced by the conventional hot emulsion technique, using different lipidic carriers (tristearin, glyceryl behenate and stearic acid) and hydrogenated phosphatidylcholine as the surfactant. The controlled release of CPA was achieved only with stearic acid microparticles. This phenomenon has been attributed to direct acid-base interactions between the basic nitrogen atoms of CPA and stearic acid. These SLMs were characterized by release studies, scanning electron microscopy and powder X-ray diffraction analyses. The obtained particles showed proper features in terms of morphology and size distribution (3.2-10.3 microm), with a drug loading of 0.15±0.04%. The influence of the SLMs carrier system on CPA stability was investigated in vitro using human whole blood. The degradation kinetic of microparticle-entrapped CPA was significantly lower from that measured for the free CPA. The overall results indicate that it was possible to achieve the encapsulation and controlled release of a polar drug, such as CPA, within a lipid matrix without resorting to the complex methods generally used for the preparation of these systems.