Preparation and in vitro evaluation of polystyrene-coated diltiazem-resin complex by oil-in-water emulsion solvent evaporation method

pH-Triggered Release of NaNO2 Corrosion Inhibitors from Novel Colophony Microcapsules in Simulated Concrete Pore Solution

Herein, pH-sensitive microcapsules containing NaNO₂ corrosion inhibitors for protection of steel reinforced concrete were synthesized via water-in-oil-in-water (W/O/W) double emulsion using colophony as the wall material. The average microcapsule size was 79.07 μm in diameter and exhibited a high encapsulation efficiency of 83.2%. Study of the release of corrosion inhibitors from microcapsules in deionized water (DI water, pH 6.8), carbonate/bicarbonate buffer solution (CBS, pH 9.1), and simulated concrete pore solution (SCPS, pH 12.6) demonstrates that the microcapsules are sensitive to pH and display higher release in alkaline media. This is the first study of colophony as an encapsulating agent for corrosion inhibitors. Furthermore, the alkaline pH-triggered release shows the suitability of its use in reinforced concrete systems. A wide thermal stability range was also found for the colophony microcapsules up to 100 °C. These high pH environments (CBS and SCPS) present pH values above the pK_a of colophony (7.2), thus triggering enhanced inhibitor release by the ionization and deprotonation of colophony shell. The higher release in CBS and SCPS is demonstrated by the increases of the corrosion inhibitor diffusion coefficient by an order of magnitude from 3.30 × 10^-17 m²/s in DI water up to 1.66 × 10^-16 m²/s for SCPS. The release performance indicates that the proposed approach can be used to encapsulate a variety of inhibitors for the protection of steel reinforcements. After immersion in different pH solutions, the corrosion potentials of a carbon steel substrate with microcapsules containing nitrite were more noble than when immersed without microcapsules and the corrosion current densities showed comparable values to free corrosion inhibitors. The formation of a passive ferric oxide layer was confirmed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy.

Formulation and Characterisation of a Combination Captopril and Hydrochlorothiazide Microparticulate Dosage Form

Cardiovascular diseases such as hypertension and cardiac failure in South African children and adolescents are effectively managed long term, using a combination treatment of captopril and hydrochlorothiazide. The majority of commercially available pharmaceutical products are designed for adult patients and require extemporaneous manipulation, prior to administration to paediatric patients. There is a need to develop an age appropriate microparticulate dosing technology that is easy to swallow, dose and alter doses whilst overcoming the pharmacokinetic challenges of short half-life and biphasic pharmacokinetic disposition exhibited by hydrochlorothiazide and captopril. An emulsion solvent evaporation approach using different combinations of polymers was used to manufacture captopril and hydrochlorothiazide microparticles. Design of experiments was used to develop and analyse experimental data, and identifyoptimum formulation and process conditions for the preparation of the microparticles. Characterisation studies to establish encapsulation efficiency, in vitro release, shape, size and morphology of the microparticles were undertaken. The microparticles produced were in the micrometre size range, with an encapsulation efficiency >75% for both hydrochlorothiazide and captopril. The microparticulate technology is able to offer potential resolution to the half-life mediated dosing frequency of captopril as sustained release of the molecule was observed over a 12-h period. The release of hydrochlorothiazide of >80% suggests an improvement in solubility limited dissolution.

Polymer-amino-functionalized silica composites for the sustained-release multiparticulate system

This study presents an interesting and promising strategy for producing an oral multiparticulate formulation of the sustained-release of diclofenac sodium (DS) consisting of subunits closed inside hard gelatin capsules (each capsule contains ~50mg of diclofenac sodium). The subunits in the form of beads were produced through the encapsulation of diclofenac sodium dispersed within a nondisintegrating polymer carrier by a silica gel functionalized with the 3-aminopropyl groups. The hybrid silica gel, which plays the role of enteric coating, was fabricated by the gelation of the liquid silica precursors mixture (i.e. tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES)) in the vapor phase of ammonia. The conducted studies reveal that the introduction of the hybrid silica gel into the solid DS dispersion facilitates prolonged release in the neutral environment of the intestine. Since the ability of the multiparticulate formulation to control the release of the drug depends on the properties of its subunits, studies involving the low temperature N₂ sorption, DSC analysis together with spectroscopic techniques (XRD, SEM, ²⁹Si MAS NMR) were conducted.

Vapour-phase method in the synthesis of polymer-ibuprofen sodium-silica gel composites

The study discusses the synthesis of polymer-silica composites comprising water soluble drug (ibuprofen sodium, IBS). The polymers selected for this study were poly(TRIM) and poly(HEMA-co-TRIM) produced in the form of permanently porous beads via the suspension-emulsion polymerization method. The acid and base set ternary composites were prepared by the saturation of the solid dispersions of drug (poly(TRIM)-IBS and/or poly(HEMA-co-TRIM)-IBS) with TEOS, and followed by their exposition to the vapour mixture of water and ammonia, or water and hydrochloric acid, at autogenous pressure. The conducted analyses reveal that the internal structure and total porosity of the resulting composites strongly depend on the catalyst which was used for silica precursor gelation. The parameters characterizing the porosity of both of the acid set composites are much lower than the parameters of the base set composites. Moreover, the basic catalyst supplied in the vapour phase does not affect the ibuprofen sodium molecules, whereas the acid one causes transformation of the ibuprofen sodium into the sodium chloride and a derivative of propanoic acid, which is poorly water soluble. The release profiles of ibuprofen sodium from composites demonstrate that there are differences in the rate and efficiency of drug desorption from them. They are mainly affected by the chemical character of the polymeric carrier but are also associated with the restricted swelling of the composites in the buffer solution after precipitation of silica gel.

Formulation of venlafaxine for once daily administration using polymeric material hybrids

OBJECTIVE

Controlled release venlafaxine for once daily administration.

METHODS

Drug resin complexation followed by polymer encapsulation. A 4(1).2(1) factorial design was used to study the effect of polymer type and core: coat ratio on the release profile and kinetics. Polymer combinations were tried for optimisation adapting the desIMNCility function. The optimised formula was tested in rabbits against commercial extended release capsules.

RESULTS

Poly-epsilon-caprolactone, poly(d, l-lactide-co-glycolide) ester and poly(d, l-lactide) ester polymers were more efficient in lowering the release rate and the initial burst release than Eudragit(®)RS100. Encapsulation at 1:1 ratio ensured complete coats and drug release sustainment. Formula prepared using 50:50 PLA/Eudragit at 1:1 ratio sustained the drug release up to 24 h with low burst release. This formula had higher venlafaxine absorption in rabbits compared to the commercial capsules.

CONCLUSIONS

The optimised formula is superior to the available once-daily trials regarding enhanced bioavailability, dosage form versatility and ease of scaling up.

Novel interpenetrated polymer network microbeads of natural polysaccharides for modified release of water soluble drug: in-vitro and in-vivo evaluation

OBJECTIVES

The objective of this work was to prepare novel interpenetrating polymer network (IPN) microbeads of tamarind seed polysaccharide and sodium alginate for controlled release of the water soluble drug, diltiazem hydrochloride.

METHODS

The diltiazem-Indion 254(®) (a cation exchange resin) complex was prepared and the resulting complex was entrapped within IPN microbeads prepared by ionotropic gelation and covalent crosslinking. Microbeads were characterized by scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) analyses, and evaluated for swelling, in-vitro release and preclinical pharmacokinetics.

KEY FINDINGS

The unformulated drug showed complete dissolution within 60min, while drug release from diltiazem-ion-exchange resin complex was extended for 2.5h but IPN microbeads extended the release for longer period. The ionically crosslinked microbeads released the drug for 6h, while dual crosslinked microbeads extended the release for 9h. The microbeads containing a higher amount of glutaraldehyde released the drug very slowly. The results of in-vivo pharmacokinetics of pure drug and drug-loaded IPN microbeads showed that the microbeads demonstrated prolonged release supporting the findings of in-vitro studies.

CONCLUSIONS

Prepared IPN microbeads showed prolonged in-vitro and in-vivo release for diltiazem, indicating that this IPN would be a versatile delivery system for water soluble drugs.

Molecular properties and evaluation of indion 234-ondansetron resinates

Ondansetron is a serotonin 5HT3 antagonist; anti-emetic drug. Bitter taste of the ondansetron is a major problem in ensuring patient compliance. The study was designed to formulate tasteless complexes of ondansetron with ion exchange resin and evaluate molecular properties of drug complex. The drug-loading process was carried out using various resins and was optimized using different drug:resin ratio and pH. Resinates were characterized by infrared spectroscopy, thermal analysis, and X-ray powder diffraction (XRPD). Indion 234 gave the best loading efficiency at drug resin ratio of 1:1.5. pH had no effect on drug loading. XRPD studies revealed that drug is in amorphous state in complex. The Infrared studies revealed complexation of secondary amine group of drug with carboxylic functional group of resin. Taste evaluation by using semiquantitative method found resonates as tasteless and agreeable. The release of drug from resinates in simulated gastric fluid was complete in 30 min. Thus, ion exchange resinates offer an effective tool for masking of bitterness and improve drug release.

Evaluation of a matrix tablet prepared with polyacrylamide-g-sodium alginate co-polymers and their partially hydrolyzed co-polymers for sustained release of diltiazem hydrochloride

Diltiazem hydrochloride (DTZ) matrix tablets were prepared using polyacrylamide-grafted sodium alginate (PAam-g-SA) co-polymers having different percentages of grafting and their partially hydrolyzed products with a view to achieve sustained release of the highly water-soluble drug. PAam-g-SA co-polymers having different percentages of grafting were synthesized by free radical polymerization using acrylamide (Aam) as monomer and ammonium persulphate (APS) as initiator, and the resulting co-polymers were subjected to alkaline hydrolysis to produce their corresponding partially hydrolyzed co-polymers. Matrix tablets of DTZ were prepared by wet granulation using either PAam-g-SA co-polymers or partially hydrolyzed PAam-g-SA co-polymers. The effect of percentage grafting, drug load and calcium gluconate (CG), used as excipient, was studied in simulated gastrointestinal fluid. While the tablets prepared using the co-polymer having higher percentages of grafting provided faster drug release (100% in 5.5 h), the tablets prepared with the corresponding hydrolyzed co-polymer released the drug slowly (71% in 12 h). This behaviour in release appeared to be controlled by the relative magnitude of the viscosity and the swelling capacity of the copolymers. Moreover, increase in drug load tended to decrease the drug release from all types of tablets and increase in the amount of CG increased the drug release. FT-IR and DSC studies revealed the absence of any interaction between the drug and the co-polymers. The matrix tablet made of partially hydrolyzed graft co-polymer having the highest percentage of grafting provided the most sustained release of the drug.