Water-soluble drugs, release from polymer

The initial rate of drug release from polymer monoliths can be slowed down by surface extraction and several such methods have been described (3,4). A controlled surface-extraction process leading to a sigmoidal drug distribution and thereby achieving nearly constant release of very water soluble drugs has been described by Lee (5, 6, 7). 

C. This could be attributed to the possible cross-linkages formed between the two polymers which thus restricted the movement of the drug molecules within the gel. The release of propranolol hydrochloride from the emulsion base, formulation D, was relatively low compared with all the hydrophilic polymeric gel formulations. This suggests that, for a water-soluble drug such as propranolol hydrochloride, polymeric-gel-based formulations are clearly the better vehicles for developing such dosage forms. 

Release and Delayed Release of Water-Soluble Drugs from Polymer Beads with Low Water Swelling... 

Highly water soluble drugs, as they are typical for oral administration, can be released from polymer beads with low (< 10%) water- but high ethanolswelling capacity at controlled rates, for up to 8 hours. The release of oxprenolol-HCl (77% water solubility) and diclofenac Na (2.6% water solubility) from drug loaded monoliths is a function of water content and crosslink density. By partial extraction of the drug loaded beads the release can be further slowed down and, in the case of oxprenolol-HCl, delayed for several hours the delay is dependent on water content of the polymer and is the result of the formation of a hydrophobic surface membrane. 

Zhu, Y., Shah, N. H., Malick, A. W., Infeld, M. H., and McGinity, J. W. (2006), Controlled release of a poorly water-soluble drug from hot-melt extrudates containing acrylic polymers, Drug Dev. Ind. Pharm., 32, 569-583. 

Tang, L. Schwartz, J.B. Porter, S.C. Schnaare, R.L. Wigent, R.J. Drug release from film-coated chlorpheniramine maleate nonpareil beads effect of water-soluble polymer, coating level, and soluble core material. Pharm. Dev. Technol. 2000, 5 (3), 383-390. 

Hydroxypropylmethyl cellulose Hydroxypropyhnethyl cellulose (HPMC) (Figure 28.2) is water-soluble cellulose ether and it can be used as hydrophilic polymer for the preparation of controlled-release tablets. Water penetrates the matrix and hydrates the polymer chains, which eventually disentangle from the matrix. Drug release from HPMC matrices follows two mechanisms, drug diffusion through the swelling gel layer and release by matrix erosion of the swollen layer. " ... 

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