Formulation of Cinnarizine for Stabilization of Its Physiologically Generated Supersaturation

Interplay of Drug-Polymer Interactions and Release Performance for HPMCAS-Based Amorphous Solid Dispersions

The interplay between drug and polymer chemistry and its impact on drug release from an amorphous solid dispersion (ASD) is a relatively underexplored area. Herein, the release rates of several drugs of diverse chemistry from hydroxypropyl methylcellulose acetate succinate (HPMCAS)-based ASDs were explored using surface area normalized dissolution. The tendency of the drug to form an insoluble complex with HPMCAS was determined through coprecipitation experiments. The role of pH and the extent of drug ionization were probed to evaluate the role of electrostatic interactions in complex formation. Relationships between the extent of complexation and the drug release rate from an ASD were observed, whereby the drugs could be divided into two groups. Drugs with a low extent of insoluble complex formation with HPMCAS tended to be neutral or anionic and showed reasonable release at pH 6.8 even at higher drug loadings. Cationic drugs formed insoluble complexes with HPMCAS and showed poor release when formulated as an ASD. Thus, and somewhat counterintuitively, a weakly basic drug showed a reduced release rate from an ASD at a bulk solution pH where it was ionized, relative to when unionized. The opposite trend was observed in the absence of polymer for the neat amorphous drug. In conclusion, electrostatic interactions between HPMCAS and lipophilic cationic drugs led to insoluble complex formation, which in turn resulted in ASDs with poor release performance.

An Insight into Eudragit S100 Preserving Mechanism of Cinnarizine Supersaturation

Generally, supersaturation of weakly basic drug solution in the gastrointestinal tract can be followed by precipitation, and this can compromise the bioavailability of drugs. The purpose of this study was to evaluate the effect of Eudragit® S100 on the pH-induced supersaturation of cinnarizine and to examine the preserving mechanism of cinnarizine supersaturation by Eudragit®. Variables, including pH of media, ionic strength, and degree of supersaturation, were studied to investigate the effects of these parameters on cinnarizine supersaturation in the presence and absence of Eudragit®. The size of the Eudragit® aggregate in solution using dynamic light scattering was determined. The effect of Eudragit® on the transport of cinnarizine through the Caco-2 membrane was also investigated. The particle size study of Eudragit® aggregates showed that the size of these aggregates become large when the pH was lowered. Supersaturation experiments also demonstrated that Eudragit® preserved higher cinnarizine supersaturation with increasing ionic strength of the solution. The phase separation behavior of cinnarizine solution as a function of the degree of the supersaturation could be readily explained by considering the drug amorphous solubility. In vitro permeation studies revealed that the rate of cinnarizine permeation across Caco-2 cells increased in the presence of Eudragit®. According to the obtained results, the aggregation status of Eudragit® and nonspecific hydrophobic cinnarizine-Eudragit® interactions seemed to be essential in determining the effect of Eudragit® on cinnarizine supersaturation.

pH-Dependent supersaturation from amorphous solid dispersions of weakly basic drugs

PURPOSE

In amorphous solid dispersions (ASDs), the chemical potential of a drug can be reduced due to mixing with the polymer in the solid matrix, and this can lead to reduced drug release when the polymer is insoluble in the dissolution media. If both the drug and the polymer composing an ASD are ionizable, drug release from the ASD becomes pH-dependent. The goal of this study was to gain insights into the pH-dependent solubility suppression from ASD formulations.

METHODS

The maximum release of clotrimazole, a weakly basic drug, from ASDs formulated with insoluble and pH-responsive polymers, was determined as a function of solution pH. Drug-polymer interactions in ASDs were probed using melting point depression, moisture sorption, and solid-state Nuclear Magnetic Resonance spectroscopy (SSNMR) measurements.

RESULTS

The extent of solubility suppression was dependent on polymer type and drug loading. The strength of drug-polymer interactions was found to correlate well with the degree of solubility suppression. For the same ASD, the degree of solubility suppression was nearly constant across the solution pH range studied, suggesting that polymer-drug interactions in residual ASD solids was independent of solution pH. The total drug release agrees with the Henderson-Hasselbalch relationship if the suppressed amorphous solubility of the free drug is independent of solution pH.

CONCLUSIONS

The mechanism of solubility suppression at different solution pHs appeared to be drug-polymer interactions in the solid-state, where the concentration of the free drug remains the same at variable pHs and the total drug concentration follows the Henderson-Hasselbalch relationship.

The effect of some acrylic polymers on dissolution of celecoxib solid dispersion formulations

OBJECTIVE

The purpose of the present study was firstly to identify the effectiveness of Eudragit® polymers (Eudragit^® RL, RS, L100-55, L100, S100 and E100) in inhibition of celecoxib precipitation from buffer solutions (pH = 6.8). Furthermore, the influence of Eudragit^® polymers on non-sink dissolution behavior of celecoxib from solid dispersions was investigated.

METHODS

Solid dispersions were prepared by the rotary evaporation method. In vitro dissolution studies, FT-IR and differential scanning calorimetry were employed to characterize the formulations.

RESULTS

The results revealed that Eudragit^® E100, L100 and S100 inhibited precipitation of celecoxib efficiently. It is understood that crystallization during the dissolution of solid dispersions could happen through crystallization from solid matrix following contact with the dissolution medium or from the supersaturated solution produced following dissolution. The supersaturated drug concentrations attained from the dissolution of Eudragit^®-celecoxib solid dispersions were almost similar, suggesting that crystallization from solid matrix did not occur readily. However, only solid dispersions containing efficient crystallization inhibitor polymers were able to maintain the supersaturated solution up to the end of the dissolution run.

CONCLUSION

Results revealed that the principal mechanism of attaining supersaturated solution of celecoxib from solid dispersions was related to crystallization inhibition from solution not from solid matrix.

Single-stranded β-1,3-1,6-glucan as a carrier for improved dissolution and membrane permeation of poorly water-soluble compounds

The ability of a water-soluble, single-stranded β-1,3/1,6-glucan (ssβ-glucan), recovered by hydrothermal treatment, to enhance the solubility and membrane permeability of poorly water-soluble compounds was examined. As a poorly water-soluble model compound, quercetin (QUE) was used. The aqueous solubility of spray-dried particles (SDPs) of QUE/ssβ-glucan was significantly enhanced compared with that of the untreated QUE powder and the physical mixture of QUE/ssβ-glucan. Fourier-transform infrared spectra and small-angle X-ray scattering suggested strong interactions between ssβ-glucan and QUE in the SDPs, which was attributable to QUE entrapment in the helical ssβ-glucan structure. The amount of QUE infused into Caco-2 cells from QUE/ssβ-glucan SDPs was 16-fold and 5-fold higher than the amount infused from untreated QUE powder and the physical mixture of QUE/ssβ-glucan, respectively. These results showed that water-soluble ssβ-glucan improved QUE dissolution and membrane permeability.