Background. The biological half life of metformin requires multiple doses which are associated with poor patient compliance. This justifies the need for a dosage form with reduced dosing frequency.

Objectives. Gums from Enterolobium cyclocarpum and Cedrela odorata trees were evaluated in formulating bioadhesive microspheres containing metformin hydrochloride, for sustained drug release. Hydroxylpropyl- methyl cellulose (HPMC) was the standard.

Material and methods. Microspheres were produced from formulations of API and either cedrela gum (FC), enterolobium gum (FE) or HPMC (FH), using a W/O solvent extraction technique. The micro- spheres were characterized using a particle size analyzer, scanning electron microscopy (SEM), differen- tial scanning calorimetry (DSC), powder X-ray diffractometer (PXRD), drug entrapment, in vitro release and mucoadhesion studies. The data was analyzed using ANOVA and t-test at p = 0.05.

Results. FT-IR spectroscopy indicated no alteration in the functional groups of metformin. A yield of 92–98% microspheres was obtained from all the formulations which had a particle size range of 72–84 μm. SEM revealed cylindrical to near-spherical particles with rough surfaces. The drug release profile showed a burst over the first 30 min followed by a steady release for about 5 h and a slow release for 5 days. Formulations containing the gums sustained the release of API for almost the same time as HPMC formulations; the ran- king order was FE > FH > FC (p > 0.05). All the formulations exhibited good concentration-dependent mucoadhesive properties.

Conclusions. The gums were suitable for formulation of mucoadhesive microspheres for sustained release of metformin. The formulations showed good release properties in an alkaline pH.

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