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The Effect of Polymer Content on the Non-Newtonian Behavior of Acetaminophen Suspension

DOI: 10.1155/2013/907471

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Acetaminophen is used as an analgesic and antipyretic agent. The aim of the study was evaluation of the effect of different polymers on rheological behavior of acetaminophen suspension. In order to achieve controlled flocculation, sodium chloride was added. Then structural vehicles such as carboxymethyl cellulose (CMC), polyvinyl pyrrolidone (PVP), tragacanth, and magnesium aluminum silicate (Veegum) were evaluated individually and in combination. Physical stability parameters such as sedimentation volume ( ), redispersibility ( ), and growth of crystals of the suspensions were determined. Also, the rheological properties of formulations were studied. The results of this study showed that the combination of suspending agents had the most physical stability and pseudoplastic behavior with some degree of thixotropy. Viscosity of suspensions was increased by adding NaCl 0.02%. Presence of PVP is necessary for improving rheological behavior of suspensions by NaCl. This may be related to the cross-linking between the carbonyl group in the PVP segment and Na+ ions. 1. Introduction A suspension is a dispersed system in which the internal phase consists of solid particles and the external phase is a liquid vehicle. Suspensions are the best conventional liquid dosage forms of drugs with high bioavailability in comparison to other dosage forms except solutions, and they have patient compliance [1, 2]. Rheological study of suspensions provides valuable information for efficient utilization, transport, and handling of materials in industrial applications [3]. The thixotropy and hysteresis loop are rheological phenomena. In non-Newtonian systems if the rate of shear was reduced once the desired maximum rate had been reached, the down curve can be displaced relative to the up curve. With pseudoplastic systems, the down curve is frequently displaced to the left of the up curve. This phenomenon, known as thixotropy, can be defined as an isothermal and comparatively slow recovery, on standing of a material, which has lost its consistency through shearing [4, 5]. The area surrounded between ascending and descending curves that is called hysteresis loop can give information about the structure breakdown and rebuilding [4, 6, 7]. Controlled flocculation and rheologic modification are important factors in preparation of suspensions. Flocculated suspensions are settled rapidly to form large loose and easily dispersible sediments [8]. Non-Newtonian polymers are utilized in the industries such as food, textile, pharmaceutical, and cosmetics. They are employed in suspensions as


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