[Effect of storage temperature on gelation of oral methylcellulose formulation].

  Heating a methylcellulose solution forms a thermal-reversible hydrogel. After the hydrogel forms, its properties change according to its temperature. However, the effects of heating this solution during storage and then cooling it are unclear. We investigated the effects of this heating and cooling on rheological and drug release characteristics. We prepared samples of methylcellulose solution (2% methylcellulose and 20% D-sorbitol) and examined them under two conditions: 1) storage for 24 hours at 4 to 30℃, 2) storage for 24 hours at 4 to 50℃, then cooling to 4℃ and maintained for 4 hours. We performed rheological investigations of viscosity, gelation temperature and gel strength, and examined the drug release characteristics by using a diffusion cell method with acetaminophen as the model drug. It was found that as the storage temperature rose, the methylcellulose solution increased in viscosity and the gelation temperature and gel strength changed. During storage at 30℃, the amount of drug released by the solution increased and the diffusion coefficient was high. When cooled to 4℃, the solution recovered its viscosity, gelation temperature, gel strength and drug release characteristics, regardless of the previous storage temperature. These results clarify that although the rheological and drug release characteristics of methylcellulose solution change with changes in storage temperature, the original characteristics are recovered after the solution is cooled to 4℃ and maintained at that temperature for four hours.

The influence of the degree of esterification on the release characteristics of in situ gelling pectin formulations for oral sustained delivery of paracetamol.

The aim of this study was to examine the effect of a change of the degree of esterification of pectin on the in situ gelation and release characteristics of 1.5% (w/v) pectin solutions over a wide pH range. Formulations of pectin with degrees of esterification of 9% (DE9) and 31% (DE31) containing complexed calcium ions formed gels in vitro at pH 1.2 as a consequence of cross-linking of the pectin chains by free calcium ions released from the complex. In vitro release of paracetamol from these gels was diffusion controlled. A sustained release of paracetamol was observed following oral administration of pectin DE9 and DE31 formulations to gastric acidity-controlled rats at pH 2.5 but only with DE9 formulations at pH 5.5. Examination of the stomach contents confirmed effective in situ gelation of pectin DE9 formulations at a gastric pH of 6 but there was no evidence of the gelation of pectin DE31 formulations at this pH.

Oral liquid in situ gelling methylcellulose/alginate formulations for sustained drug delivery to dysphagic patients.

BACKGROUND: Elderly patients with swallowing dysfunction may benefit from the oral administration of liquid dosage forms with in situ gelling properties. AIM: We have designed in situ gelling liquid dosage formulations composed of mixtures of methylcellulose, which has thermally reversible gelation properties and sodium alginate, the gelation of which is ion-responsive, with suitable rheological characteristics for ease of administration to dysphagic patients and suitable integrity in the stomach to achieve a sustained release of drug. METHOD: The rheological and gelation characteristics of solutions containing methylcellulose (2.0%) and sodium alginate (0.25-1.0%) were assessed for their suitability for administration to dysphagic patients. The gel strength and in vitro and in vivo release characteristics of gels formed by selected formulations were compared using paracetamol as a model drug. RESULTS: Mixtures of 2.0% methylcellulose and 0.5% alginate containing 20% d-sorbitol were of suitable viscosity for ease of swallowing by dysphagic patients and formed gels at temperatures between ambient and body temperature allowing administration in liquid form and in situ gelation in the stomach. In vitro release of paracetamol from 2.0% methylcellulose/0.5% alginate gels was diffusion-controlled at pH 1.2 and 6.8. Measurement of plasma levels of paracetamol after oral administration to rats of a 2.0% methylcellulose/0.5% alginate formulation showed improved sustained release compared to that from 2.0% methylcellulose and 0.5% alginate solutions and from an aqueous solution of paracetamol. CONCLUSIONS: Solutions of mixtures of methylcellulose and alginate in appropriate proportions are of suitable consistency for administration to dysphagic patients and form gels in situ with sustained release characteristics.

In situ gelling formulation based on methylcellulose/pectin system for oral-sustained drug delivery to dysphagic patients.

BACKGROUND: Oral-sustained release gel formulations with suitable rheological properties have been proposed as a means of improving the compliance of dysphagic and geriatric patients who have difficulties with handling and swallowing oral dosage forms. AIM: We have modified the rheological and release properties of thermally reversible methylcellulose solutions by admixture with pectin, the gelation of which is ion-responsive, with the aim of formulating an in situ gelling vehicle suitable for oral-sustained drug delivery. METHOD: Gels formed by solutions containing methylcellulose (1.0-2.0%) and pectin (0.5-2.0%) were assessed for suitable gel strength, and in vitro and in vivo release of paracetamol. RESULTS: Addition of 1.5% pectin to a 2.0% methylcellulose formulation containing 20% d-sorbitol and calcium ions in complexed form increased the gel strength and provided a formulation with a suitable viscosity for ease of swallowing by dysphagic patients. Gels formed in situ after oral administration of this formulation retained their integrity in the rat stomach for sufficient time for sustained release to be achieved. In vitro release of paracetamol from methylcellulose, pectin, and methylcellulose/pectin gels was diffusion-controlled. Plasma levels of paracetamol after oral administration to rats (gastric pH 2.6 and 5.5) of a solution including 2.0% methylcellulose/1.5% pectin showed improved sustained release compared with that from both 2.0% methylcellulose and 1.5% pectin solutions. CONCLUSIONS: The addition of suitable concentrations of pectin to methylcellulose solutions produces in situ gelling formulations with suitable viscosity for administration to dysphagic patients and improved sustained release characteristics.

Carrageenan gels for oral sustained delivery of acetaminophen to dysphagic patients.

We have designed gel formulations for the oral administration of acetaminophen with suitable rheological characteristics for ease of administration to patients with swallowing difficulties and sufficient integrity in the stomach to achieve a sustained release of this drug. Gels formed by agar and ι-carrageenan were assessed for suitable gel strength and in vitro and in vivo release characteristics. Comparison of 1.5% ι-carrageenan gel with 0.5% agar gel demonstrated improved sustained release properties of the ι-carrageenan gel. Gel formed by ι-carrageenan has suitable rheological and sustained release characteristics for potential use as vehicles for oral delivery of drugs to dysphagic patients.

Effect of D-sorbitol on the thermal gelation of methylcellulose formulations for drug delivery.

The aim of this study was to examine the effect of D-sorbitol on the gelation characteristics of methylcellulose in aqueous solution. The addition of D-sorbitol at concentrations of between 25 and 30% (w/v) to 1.0-2.0% (w/v) methylcellulose solutions reduced the gelation temperature from approximately 53 degrees Celsius to values between ambient and 37 degrees Celsius and increased the strength of the gel. The in vitro release of acetaminophen (paracetamol) from 2.0% (w/v) methylcellulose gels containing 20-30% (w/v) D-sorbitol gel was diffusion-controlled.

In situ gelling xyloglucan/alginate liquid formulation for oral sustained drug delivery to dysphagic patients.

BACKGROUND: The oral administration of liquid dosage forms of suitable consistency and with sustained release characteristics may provide a means of improving the compliance of geriatric patients who experience difficulties in swallowing conventional solid dosage forms. AIM: We have designed and evaluated liquid preparations for administration to dysphagic patients, composed of aqueous mixtures of xyloglucan, which has thermally reversible gelation characteristics, and sodium alginate, which has ion-responsive gelation characteristics. METHOD: The gelation and in vitro and in vivo release characteristics of liquid formulations containing appropriate concentrations of xyloglucan and sodium alginate with mannuronate/guluronate ratios of either 0.5 or 0.8 were assessed. RESULTS: Aqueous mixtures of 1.5% xyloglucan and 0.5% alginate had suitable viscosities for ease of swallowing and appropriate gelation temperatures (approximately 33 degrees C) to ensure in situ gelation following oral administration. The in vitro release of paracetamol at pH 5.0 from gels formed by these formulations and also by a 1.5% xyloglucan solution was diffusion-controlled. Plasma levels of paracetamol after oral administration to gastric-acidity controlled rats (pH 5) of a solution containing 1.5% xyloglucan/0.5% alginate showed that a more sustained release was achieved from the gels formed by the in situ gelation of this formulation compared with that of a 1.5% xyloglucan solution. Visual observation of the contents of the rat stomach after oral administration showed that the inclusion of alginate in the xyloglucan solutions was effective in reducing gel erosion, so sustaining drug release. CONCLUSIONS: Liquid formulations of xyloglucan and sodium alginate in appropriate proportions are of suitable consistency for ease of administration to dysphagic patients and form gels in situ in the rat stomach capable of sustaining the release of paracetamol over a 6-hour period.