Formulation and evaluation of colon targeted tablets containing simvastatin solid dispersion

Solid dispersions (SDs) of simvastatin with mannitol, Ineutic®, Pluronic® F-68, PEG 4000 and PVP K-30 were prepared and evaluated to deliver simvastatin to the colon in a pre-solubilized form. The formula of choice was compressed into fast disintegrating tablets using drug compatible excipients and was coated with Eudragit® S100 as a pH-responsive polymer. We investigated the effects of several variables related to both SD preparation (carrier type, combined carriers and drug to carrier ratio) and tablet coating (coat level and type of plasticizer) on drug dissolution. Differential scanning caloremitry (DSC) and scanning electron microscopy (SEM) proved drug amorphization in SDs. The 1:5 simvastatin/ Pluronic® SDs showed the greatest improvement in dissolution efficiency (12.2-fold) at the lowest carrier ratio. The coating level was critical for determining the duration of the lagphase. Best results were given by the 10% coat (20:2:1 w/w Eudragit S100/ triethylcitrate/ talc). This formula resisted pre-colonic pH values and showed an adequate lag time for the intended colonic targeting (4 h), followed by an immediate release phase (t50%=249 min) in pH 7.4. The proposed coated tablets may provide a colonic delivery system for simvastatin with improved bioavailability.