Flocculation of sulfamerazine suspensions by a cationic polymer

Association between the physical stability of flurbiprofen suspension and the interaction of HPMC/SDS

The anionic surfactant sodium dodecylsulfate (SDS) has improved the physical stability of flurbiprofen (FBP) suspension, which was suspended by 0.2% (w/v) hydroxypropylmethyl cellulose (HPMC, K4M). Therefore, the physical stability of FBP suspensions and the interaction of HPMC/SDS were studied, and a certain association between them was revealed. The anti-solvent precipitation method was used to prepare suspensions. The apparent drug concentration from different sites was evaluated to get the dispersion of drug actually. The process of flocculation and deflocculation with the addition of SDS was caught by analyzing the morphology of the suspended particles. The physical stability of the FBP suspensions was characterized mainly by measuring the re-dispersion time, the zeta potential and particle size. Meanwhile, conductivity measurements were carried out to obtain the characteristic concentrations of SDS in HPMC/SDS system. The viscosities, the abilities for improving the solubility and wettability of FBP in the separate and mixed HPMC/SDS solutions were also contrasted respectively. The suspensions prepared with HPMC/SDS possessed better physical stability. The suspensions were uniform when the concentration of SDS was between the critical adsorption concentration (CAC) and the polymer saturation point (PSP). After PSP, the uniformity became worse and worse until the SDS was enough to form a deflocculation state. Besides, the re-dispersion time of FBP suspensions was longest when the concentration of SDS around CAC and shorter by shorter after the critical micelle concentration (CMC). The article provided a new sight on the relation between the interaction of excipient matrix and pharmaceutical preparations.

Evaluation of ophthalmic suspensions using surface tension

Uniformity and precision of single dose are required for ophthalmic suspensions including water-insoluble ingredients. Solid sediments formed after standing still must be immediately re-dispersible and distributed homogeneously before use. However, selection of an appropriate water-soluble polymer as suspending agent is a challenging problem. In this report, the relationship between the surface tension and the re-dispersibility of suspensions was investigated. The surface tension of 0.1 w/v% fluorometholone suspensions began to decline from 74 mN/m at 0.0001 w/v% of hydroxypropylmethylcellulose (HPMC) and became almost constant at 52 mN/m at 0.01 w/v% of HPMC. Re-dispersion time was less than 4 s when HPMC was present at concentrations between 0.0001 w/v% and 0.01 w/v%. At these concentrations, aggregation of suspended particles was not observed. When indomethacin suspensions at 1.0 w/v% concentration were used, the surface tension began to decline from 73 mN/m at 0.0005 w/v% HPMC and became constant at 50 mN/m at 0.005 w/v% HPMC. The suspension also showed good re-dispersibility, and a uniform suspension was obtained between 0.0005 w/v% and 0.005 w/v% of HPMC. The time required for re-dispersion was less than 17 s. The change of surface tension showed a good correlation with the concentration of HPMC in ophthalmic suspensions having good re-dispersibility. Measurement of the surface tension of suspensions provided the optimal concentration of the water-soluble polymers for the suspensions of well re-dispersible characteristics. Evaluation of ophthalmic suspension using surface tension is a good strategy for formulation of suspending pharmaceutical products in the ophthalmic area.

Interaction of xanthan gum with suspended solids

Xanthan gum was adsorbed significantly by magnesium carbonate, aluminum hydroxide, zinc oxide, and calcium carbonate, giving Langmuir-type isotherms. Saturation adsorption was higher from 0.9% NaCl than from water due to reduced mutual repulsion of polymer segments in the presence of the salt. Adsorption resulted from electrostatic attraction between positively charged particles and the negatively charged polymer. zeta-Potential measurements correlated with the adsorption data but were not predictive of the flocculation state. The result indicate that flocculation of magnesium carbonate and aluminum hydroxide by xanthan gum is consistent with a bridging mechanism.

Flocculation effect of xanthan gum in pharmaceutical suspensions

The particulate structure in suspensions of magnesium carbonate, aluminum hydroxide, calcium carbonate, and zinc oxide was assessed by sedimentation volume studies, measurement of particle size by an electronic particle sizer, and visualization by microscopy. The results of the particle-size measruement did not always agree with results from the other techniques. magnesium carbonate, aluminum hydroxide, and zinc oxide were flocculated in water. The addition of xanthan gum increased flocculation of magnesium carbonate and aluminum hydroxide and apparently caused partial deflocculation of zinc oxide suspensions. Calcium carbonate suspensions were deflocculated in water, and xanthan gum did not significantly change the properties. Studies with sodium chloride showed that flocculation cannot be attributed to changes in double-layer repulsion. Flocculation in the suspensions studied appeared to be consistent with a bridging mechanism.