Polymer–Magnesium Aluminum Silicate Composite Dispersions for Improved Physical Stability of Acetaminophen Suspensions

The aims of this study were to characterize the morphology and size of flocculates and the zeta potential and rheological properties of polymer–magnesium aluminum silicate (MAS) composite dispersions and to investigate the physical properties of acetaminophen (ACT) suspensions prepared using the composite dispersions as a flocculating/suspending agent. The polymers used were sodium alginate (SA), sodium carboxymethylcellulose (SCMC), and methylcellulose (MC). The results showed that SA, SCMC, and MC could induce flocculation of MAS by a polymer-bridging mechanism, leading to the changes in the zeta potential of MAS and the flow properties of the polymer dispersions. The microscopic morphology and size of the flocculates was dependent on the molecular structure of the polymer, especially ether groups on the polymer side chain. The residual MAS from the flocculation could create a three-dimensional structure in the SA–MAS and SCMC–MAS dispersions, which brought about not only an enhancement of viscosity and thixotropic properties but also an improvement in the ACT flocculating efficiency of polymers. The use of polymer–MAS dispersions provided a higher degree of flocculation and a lower redispersibility value of ACT suspensions compared with the pure polymer dispersions. This led to a low tendency for caking of the suspensions. The SCMC–MAS dispersions provided the highest ACT flocculating efficiency, whereas the lowest ACT flocculating efficiency was found in the MC–MAS dispersions. Moreover, the added MAS did not affect ACT dissolution from the suspensions in an acidic medium. These findings suggest that the polymer–MAS dispersions show good potential for use as a flocculating/suspending agent for improving the rheological properties and physical stability of the suspensions

Transdermal and Skin-Targeted Drug Delivery

The application of therapeutic agents to the skin addresses three general objectives: (a) the treatment of a variety of dermatologic diseases: (b) the “targeted” delivery of drugs to deeper subcutaneous tissues, with a concomitant reduction in systemic exposure; and (c) so-called transdermal admin-istration to elicit a systemic pharmacological effect. Recently, significant progress towards all three goals has been recorded, and the level of research and development activity remains high. We aim to discuss these advances from mechanistic and clinical standpoints. For the topical treatment of skin disease, novel vehicles (e.g., stabilized, supersaturated systems and liposomal formulations) have led to dramatic improvements in local drug bioavailability. Transdermal delivery of drugs for systemic effect, though limited in terms of the number of compounds, is perhaps the most commercially successful (in terms of the number of products) of the controlled release technologies. Considerable activity continues to enhance drug delivery (and hence to extend the range of drugs for which transdermal delivery can be used). Existing patches use formulations that contain solvents and adjuvants capable of reducing the barrier function of the skin. Much effort is directed at iontophoresis (electrically enhanced transport), particularly for small peptides that are difficult to administer by other routes. “Reverse iontophoresis” may allow the extraction of glucose (without skin puncture) so that continuous, noninvasive monitoring of blood sugar in diabetics approaches realization. In the not too distant future, the skin may also play a role not only in drug delivery, but also with re-spect to measurements in clinical chemistry