Release of furosemide from multiple-unit and single-unit preparations containing different viscosity grades of sodium alginate.

The release characteristics and the effect of viscosity of sodium alginate on the release rate of furosemide (a rather poorly soluble drug) from hard gelatin capsules (single-unit), and minitablets (multiple-unit) filled in hard gelatin capsules, were evaluated. Swelling and erosion experiments showed a different behavior for each viscosity grade. Polymer characteristics influenced significantly the release of the drug from the preparations prepared and tested. The results indicate that erosion plays a significant role, accelerates release rate and shortens duration of drug release. Low viscosity formulations exhibited a greater erosion, and drug release was completed in 4 hours. Medium viscosity formulations showed intermediate erosion, while high viscosity formulations exhibited less erosion, and drug release was completed in 8 hours. The minitablets always displayed lower release and dissolution efficiency values than the capsules, and as the viscosity increased, the difference of dissolution efficiency between the two formulations increased accordingly. The results further indicated that the multiple-unit system demonstrated a more pronounced sustained effect than the single-unit, and therefore, it is a more suitable preparation for sustained release delivery of poorly soluble drugs. Analysis of release data indicate a rather zero-order release mechanism, which may be attributed mainly to swelling and an erosion/dissolution process.