Pharmaceutical Technology: Controlled Drug Release, Volume 2

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MULTIPARTICULATES [CH. 13 143 rev min −1 for 30 min and then cooled to 20°C while still stirring. The resultant microcapsules were separated by filtration, washed four times with petroleum ether (boiling point, 40–60°C), dried in a stream of nitrogen and stored in a desiccator. Preparation of mixtures Non-microencapsulated mixtures of poly (DL-lactic acid) and phenobarbitone (ratios 1:1 and 1:2) were prepared by mixing the powders for 10 min. Preparation of tablets Tablets were prepared from both the microcapsules and mixtures using a Dartec Ltd universal testing machine. The quantity of drug contained was a nominal 200 mg and the punch diameter was 10 mm. Compression was at a constant rate of 1 kN s −1 with tablets prepared at 2, 5 and 10 kN. The tensile strength of the tablets was calculated using the formula T s =2P/Dtπ. The characteristics of the tablets prepared are shown in Table 1. Table 1—Characteristics of tablets prepared from microcapsules and mixtures of polymer and drug Particle size measurements A Coulter counter (model TA II) attached to an Apple computer (IIe) was used for all particle size measurements.
144 CH. 13] A COMPARISON OF DISSOLUTION PROPERTIES Fig. 1—Scanning electron micrograph of an individual microcapsule showing plates of DL-PLA on the surface (coret:coat ratio, 1:1). Scanning electron microscopy A scanning electron microscope (Philips 501B) was used to examine both microcapsules and mixtures, as well as the surface characteristics of the tablets prepared from Dissolution studies The computerized automatic dissolution apparatus utilized a Philips P1 18620 UV spectrophotometer connected to an Opus PC III computer. Aqueous buffer (1l; pH 2, 7 or 9) was used at a temperature of 37±0.5°C and a stirring rate of 100 rev min −1 . Read-out was every 5 min for 2 h at pH 2, every 30 min for 6 h at pH 7 and every 60 min for l2 h at pH 9. RESULTS AND DISCUSSION The appearance of the individual microcapsules is shown in Fig. 1. Most individual microcapsules are approximately spherical and show a surface made up of deposited plates of poly(DL-lactic acid) in which the drug is embedded. Many of the larger microcapsules are cemented together by further plates of poly(DL-lactic acid). The effect of compression on these microcapsules is shown in Fig. 2. At a compressive force of 2 kN (Fig. 2(a)) the electron micrograph of the tablet fracture surface shows that the microcapsules, while distorted, remain essentially intact and rounded, with a relatively open porous structure to the tablet as a whole. At 10 kN force (Fig. 2(b)) the microcapsules at the fracture are flattened, cracked and distorted so that the fracture surface shows a far less open, porous aspect. Both of these ‘microcap’ tablets have a very different appearance from that produced by the simple mixture (Fig. 3), where the individual plates of poly(DL-lactic acid) are mixed with the drug crystals in an open structure from which release would be easily
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PHARMACEUTICAL TECHNOLOGY Controlle
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3 TABLET MACHINE INSTRUMENTATION IN
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First published in 1991 by ELLIS HO
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7 10 Controlled delivery of theophy
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Slow and steady wins the race Poems
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1 Influence of drug solubility in t
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CH. 1] INFLUENCE OF DRUG SOLUBILITY
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24 MATRIX FORMULATIONS [CH. 2 MATER
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26 MATRIX FORMULATIONS [CH. 2 Fig.
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28 MATRIX FORMULATIONS [CH. 2 Table
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30 MATRIX FORMULATIONS [CH. 2 The e
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34 CH. 3] THE FORMULATION OF SUSTAI
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4 Statistical optimization of a con
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MATRIX FORMULATIONS [CH. 4 45 (4) G
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MATRIX FORMULATIONS [CH. 4 47 Fig.
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Columns 1-4 lead to the matrix of e
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MATRIX FORMULATIONS [CH. 4 51 Table
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MATRIX FORMULATIONS [CH. 4 53 Fig.
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Fig. 5—Linearization of the relea
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58 MATRIX FORMULATIONS [CH. 5 Pevik
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60 MATRIX FORMULATIONS [CH. 5 The d
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6 Controlled release matrix tablets
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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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194 INDEX dry granulation, 43 elect
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Pharmaceutical Technology: Controlled Drug Release, Volume 2

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