Relation between structural and release properties in a polysaccharide gel system

Effect of cations on the microstructure and in-vitro drug release of κ- and ι-carrageenan liquid and semi-solid aqueous dispersions

Objectives

The main objective of this study was to determine the effect of potassium and calcium ions on the microstructure and release dynamics of kappa (κ) and iota (ι) carrageenan.

Methods

The microstructure of the dispersions was imaged using a cryogenic scanning electron microscope. Franz-cell diffusion apparatus was used to determine the release kinetics of a model hydrophilic drug, sodium fluorescein, incorporated in selected polymer dispersions. Release profiles were analysed using Higuchi, Korsmeyer-Peppas and dual first-order models.

Key Findings

Cryogenic scanning electron microscope images showed that κ-carrageenan forms hexagonal structures, whereas ι-carrageenan forms rectangular pores at low cation concentrations. In-vitro release studies showed sustained release profiles for all carrageenan systems; however the model drug, fluorescein, diffusion from ι-carrageenan with 0.06% w/v calcium was significantly higher than other ι-carrageenan systems. This may be attributed to improved tortuosity of this system. However further increase in cation concentration led to a reduction in fluorescein release from the matrices. The dual first-order release model illustrated two distinct release rates, an initial rapid release followed by a slow diffusion of fluorescein from the carrageenan matrices.

Conclusions

The observed microstructural differences may account for the well known variation in mechanical properties of κ- and ι-carrageenan gels. The dual first order release model adds a new tool in the elucidation of release mechanisms from polymer matrices, where parallel processes contribute to drug release.

Carboxymethyl mungbean starch as a new pharmaceutical gelling agent for topical preparation

An application of carboxymethyl mungbean starch (CMMS) as a gelling agent in the topical pharmaceutical preparation was investigated. CMMS was prepared using specific conditions that yielded a high-viscosity product. Polymer gels and gel bases were prepared at 1-10% (wt/wt), and physicochemical studies were carried out in comparison with four standard gelling agents: carbopol 940 (CP), hydroxypropylmethyl cellulose (HPMC), methyl cellulose (MC), and sodium carboxymethyl cellulose (SCMC). Piroxicam was used as a model drug to study the drug release profile of the gel formulations. The tackless, greaseless, and transparent CMMS gels exhibited pseudoplastic behavior with thixotropy at concentrations less than 5% (wt/wt). At a concentration of 5% (wt/wt) and higher, the semisolid gels showed plastic flow characteristics. Viscosity and X-ray diffraction results indicated a good compatibility between CMMS and the acidic piroxicam. No precipitation of piroxicam or phase separation was observed during a stability test. The release rate of piroxicam from 3% (wt/wt) CMMS gel was 1,003.79 +/- 105.08 microg/cm(2), which was comparable with 947.66 +/- 133.70 microg/cm(2) obtained from a 0.5% (wt/wt) carbopol formulation. The release profiles of both formulations were consistent and remained unchanged after 2 months' storage. Viscosity played an important role in controlling the release rate of low concentration CMMS formulations by regulating the drug diffusion. At a concentration of 5% (wt/wt) CMMS and higher, the release rates of piroxicam were not significantly different. A plausible explanation based on the nature of the gelling agent was proposed. Stability and drug release profiles of CMMS and commercial gelling agents were compared. The results supported the potential use of CMMS as a new, effective gelling agent for topical gel preparation.