Sustained Release from Precirol® (Glycerol Palmito-Stearate) Matrix. Effect of Mannitol and Hydroxypropyl Methylcellulose on the Release of Theophylline

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Abstract
The release of theophylline embedded in a Precirol® (glycerol palmitostearate) matrix containing varying amounts of mannitol and/or hydroxypropyl methyl cellulose 4000 (HPMC) was studied. The results indicated that HPMC or mannitol when incorporated alone, the drug release followed the diffusion-controlled matrix model where the quantity of drug released was proportional to the square root of time. The release rate was found to increase with increase in the amount of HPMC or mannitol in the matrix. When both mannitol and HPMC were incorporated in the matrix, the mechanism of release changed from the Higuchi model to a first-order release. A linear relationship was found between the fraction of HPMC or mannitol in the matrix and the rate constant. An optimum combination of Precirol®, mannitol and HPMC was found for a 12 hour theophyll ine sustained release preparation