Development and release mechanism of diltiazem HCl prolonged release matrix tablets

A coated matrix tablet formulation has been used to develop controlled release diltiazem HCl (DIL) tablets. The developed drug delivery system provided prolonged drug release rates over a defined period of time. DIL tablets prepared using dry mixing and direct compression and the core consisted of hydrophilic and hydrophobic polymers such as hydroxypropylmethylcellulose (HPMC), Eudragits RLPO/RSPO, microcrystalline cellulose, and lactose. Tablets were coated with Eudragit NE 30D, and the influence of varying the inert hydrophobic polymers and the amount of the coating polymer were investigated. The release profile of the developed formulation was described by the Higuchi model. Stability trials up to 6 months displayed excellent reproducibility.

Chitosan derivatives alter release profiles of model compounds from calcium phosphate implants

The aim of the current study was to evaluate the impact of chitosan derivatives, namely N-octyl-chitosan and N-octyl-O-sulfate chitosan, incorporated in calcium phosphate implants to the release profiles of model drugs. The rate and extent of calcein (on M.W. 650 Da) ED, and FITC-dextran (M.W. 40 kDa) on in vitro release were monitored by fluorescence spectroscopy. Results show that calcein release is affected by the type of chitosan derivative used. A higher percentage of model drug was released when the hydrophilic polymer N-octyl-sulfated chitosan was present in the tablets compared with the tablets containing the hydrophobic polymer N-octyl-chitosan. The release profiles of calcein or FD from tablets containing N-octyl-O-sulfate revealed a complete release for FD after 120 h compared with calcein where 20% of the drug was released over the same time period. These results suggest that the difference in the release profiles observed from the implants is dependent on the molecular weight of the model drugs. These data indicate the potential of chitosan derivatives in controlling the release profile of active compounds from calcium phosphate implants. (C) 2009 Elsevier Ltd. All rights reserved.

Novel inclusion complex of ibuprofen tromethamine with cyclodextrins: Physico-chemical characterization

Guest-host interactions of ibuprofen tromethamine salt (Ibu.T) with native and modified cyclodextrins (CyDs) have been investigated using several techniques, namely phase solubility diagrams (PSDs), proton nuclear magnetic resonance (H-1 NMR), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffractometry (XRPD). scanning-electron microscopy (SEM) and molecular mechanics (MM). From the analysis of PSD data (A(L)-type) it is concluded that the anionic tromethamine salt of ibuprofen (pK(a) = 4.55) forms 1: 1 soluble complexes with all CyDs investigated in buffered water at pH 7.0, while the neutral form of Ibu forms an insoluble complex with beta-CyD (B-S-type) in buffered water at pH 2.0. Ibu.T has a lower tendency to complex with beta-CyD (K-11 = 58 M-1 at pH 7.0) compared with the neutral Ibu (K-11 = 4200 M (1)) in water. Complex formation of Ibu.T with beta-CyD (Delta G degrees = -20.4 kJ/mol) is enthalpy driven (Delta H degrees = -22.9 kJ/mol) and is accompanied by a small unfavorable entropy (Delta S degrees = -8.4 J/mol K) change. H-1 NMR studies and MM computations revealed that, on complexation, the hydrophobic central benzene ring of lbu.T and part of the isobutyl group reside within the beta-CyD cavity leaving the peripheral groups (carboxylate, tromethamine and methyl groups) located near the hydroxyl group networks at either rim of beta-CyD. PSD, H-1 NMR, DSC, FT-IR, XRPD, SEM and MM studies confirmed the formation of Ibu.T/beta-CyD inclusion complex in solution and the solid state. (C) 2009 Elsevier B.V. All rights reserved.

A revised classification for direct tooth-colored restorative materials

Composite resins and glass-ionomer cements were introduced to dentistry in the 1960s and 1970s, respectively. Since then, there has been a series of modifications to both materials as well as the development other groups claiming intermediate characteristics between the two. The result is a confusion of materials leading to selection problems. While both materials are tooth-colored, there is a considerable difference in their properties, and it is important that each is used in the appropriate situation. Composite resin materials are esthetic and now show acceptable physical strength and wear resistance. However, they are hydrophobic, and therefore more difficult to handle in the oral environment, and cannot support ion migration. Also, the problems of gaining long-term adhesion to dentin have yet to be overcome. On the other hand, glass ionomers are water-based and therefore have the potential for ion migration, both inward and outward from the restoration, leading to a number of advantages. However, they lack the physical properties required for use in load-bearing areas. A logical classification designed to differentiate the materials was first published by McLean et al in 1994, but in the last 15 years, both types of material have undergone further research and modification. This paper is designed to bring the classification up to date so that the operator can make a suitable, evidence-based, choice when selecting a material for any given situation.

Synthesis and properties of polyelectrolyte microgel particles

A series of cationic poly(N-isopropylacrylamide/4-vinylpyridine) [poly(NIPAM/4-VP)] polyelectrolyte co-polymer microgels have been prepared by surfactant free emulsion polymerization (SFEP) with varying compositions of 4-VP and NIPAM. The compositions of 4-VP were 15, 25, 35, 45, 55 wt.% relative to NIPAM. The temperature and pH responsive swelling–deswelling properties of these microgels have been investigated using dynamic light scattering (DLS) and electrophoretic mobility measurements. DLS results have shown that the particle diameter of the poly(NIPAM/4-VP) microgels decreases with increasing concentration (wt.%) of 4-VP over the 20–60 °C temperature range due to the increased amount of hydrophobic group. The particle size of all poly(NIPAM/4-VP) microgel series increases with decreasing pH, as the 4-VP units become more protonated at low pH below the pKa (5.39) of the monomer 4-VP. Electrophoretic mobility results have shown that electrophoretic mobility increases as the temperature/pH increases at a constant background ionic strength (1 × 10− 4 mol dm− 3 NaCl). These results are in good agreement with DLS results. The temperature/pH sensitivity of these microgels depends on the ratio of NIPAM/4-VP concentration in the co-polymer microgel systems. The combined temperature/pH responsiveness of these polyelectrolyte microgels can be used in applications where changes in particle size with small change in pH or temperature is of great consequence.