Pharmaceutical Technology: Controlled Drug Release, Volume 2

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CH. 2] THE EFFECT OF ELECTROLYTES AND DRUGS 27 Table 2—The effect of additives on the cloud points of 2% HPMC K100 gels Propranolol hydrochloride and promethazine hydrochloride increased the gel points and no straight line relationship existed, indicating that at higher concentrations these drugs enable the polymer to hydrate to a much larger extent than at lower concentrations. Promethazine forms micelles at concentrations>0.5% w/v [9], which may be responsible for this behaviour. No critical micellar concentration is known for propanolol hydrochloride but from studies performed it is weakly surface active. The response of HPMC to these drugs may be associated with this surface activity.
28 MATRIX FORMULATIONS [CH. 2 Table 3—The effect of additives on the cloud points of 2% HPMC K15M gels Compounds including ethanol and polyethylene glycol increase the gel point by what is thought to be absorption of the large ion of relatively low water affinity onto the macromolecule [10], carrying with it water molecules and raising the degree of hydration [11]. However, differences were found between PEG 400 and PEG 6000 (Table 2) which caused salting in and out respectively, indicating a molecular weight dependence for PEG on the cloud point. The anionic surfactant sodium lauryl sulphate caused a salting in of the HPMC K100, probably by mechanisms similar to those of propanolol hydrochloride and promethazine hydrochloride. The effect of salts on the disintegration of tablets Touitou and Donbrow [8] have described three different kinds of responses when matrices were exposed to fluids containing solutes, namely (a) rapid disintegration, (b) gradual attrition and (c) maintenance of integrity. In Table 4 three different responses are shown to occur when HPMC K15M matrices without drug were exposed to disintegration tests. At low ionic strengths the matrices were unaffected by electrolytes and hydration occurred to produce an intact gel layer. At
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CH. 6] CONTROLLED RELEASE MATRIX TA
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7 A new ibuprofen pulsed release or
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CH. 7] A NEW IBUPROFEN PULSED RELEA
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90 CH. 8] TOPICAL RELEASE AND PERME
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104 MULTIPARTICULATES [CH. 9 parace
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108 MULTIPARTICULATES [CH. 9 Fig. 2
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118 CH. 10] CONTROLLED DELIVERY OF
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126 CH. 11] THE EFFECT OF FOOD ON G
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128 CH. 11] THE EFFECT OF FOOD ON G
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132 CH. 12] BIODEGRADABLE POLYMERS
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142 CH. 13] A COMPARISON OF DISSOLU
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156 OPHTHALMIC FORMULATION [CH. 14
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162 CH. 15] A SUSTAINED RELEASE OPH
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172 IMPLANTS [CH. 16 The purpose of
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174 IMPLANTS [CH. 16 times with 5 m
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176 IMPLANTS [CH. 16 noted that the
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178 IMPLANTS [CH. 16 Fig. 1—The e
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180 IMPLANTS [CH. 16 Table 3—Tobr
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184 CH. 17] SILICON MATRIX SYSTEMS
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194 INDEX dry granulation, 43 elect
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Pharmaceutical Technology: Controlled Drug Release, Volume 2

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