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Ascorbic acid has been fluidized and microencapsulated with three different hydrophobic coating materials by the top-spray method. The experiments were conducted with polymethacrylate coating material formulated as a water dispersion, and ethyl-cellulose and waxy coating material both formulated as organic solutions. Characteristics of the fluidized bed procedure in conical geometry have been determined by estimation of two parameters: bed porosity and total pressure drop. A satisfactory agreement between experimental and calculated values has been reached. The following properties of the microencapsulated ascorbic acid have been determined: core content, bulk and tapped density, crystal size distribution prior and after microencapsulation, surface morphology and release profile. The comparison and evaluation of different hydrophobic coating materials have been performed on the basis of these findings.

Hot-melt coating process (HMCP) was applied to develop a lipid based oral controlled release matrix system (tablet) to deliver highly aqueous soluble drugs using paracetamol as a model drug. Granules prepared from paracetamol and particular filler were coated with different levels of lipid and then compressed into tablets to get controlled/sustained delivery of the drug over an optimum period. Process parameters were optimized with particular focus on fluidization pattern during HMCP proposing a 'design space' with 'Quality by Design' (QbD) concept in mind. The results demonstrated that the granule composition influenced the drug release pattern, and the rate of release could be manipulated by varying the amount of lipid in the formulation. The in vitro release profile of the drug was pH-independent and the most promising release profile was obtained from tablets prepared from granules with the water-soluble filler, lactose, and coated at 9% (w/w) level with a lipid, glyceryl behanate. In vivo plasma profiles of the drug were predicted from the in vitro release profile data by convolution analysis which confirmed that the lactose based formulation with 9% (w/w) lipid coating on the granules would be suitable for controlled delivery of the drug over a period of 12 h making the formulation suitable for highly water soluble drug candidates like paracetamol with twice daily dose regimen. Moreover, the dissolution data adequately fitted into Higuchi model suggesting that the drug release occurred predominantly by diffusion.

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