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Avicel for Suspensions

What preservatives can be used with Avicel RC-591 and Avicel CL-611?
Answer: Any of the more commonly used pharmaceutical preservatives can be used, e.g. the parabens have been used quite effectively with these components.  

Avicel RC-591 suspensions require high sheer to activate.  What processing conditions do you recommend for batches of many sizes?
Answer: In line homogenization is recommended for the use with this product because it is scale independent. If this option is not available, high shear point dispersion should be utilized, e.g. a rotor stator type disperser. 

What is the sodium content of Avicel RC-591 and Avicel CL-611?
Answer: The sodium content of Avicel RC-591 is typically 0.8% and Avicel CL-611 is typically 1.2%.  

How is a suspension containing Avicel RC-591 prepared?
Answer: Avicel RC-591 should be dispersed in water prior to the addition of other formulation ingredients. The functionality of Avicel RC-591 may be severely affected when other ingredients are added to the water first. If you are using a preservative, such as methyl and/or propylparaben or sodium benzoate, these are the only exception to the “Avicel first” rule. These should be added to the water prior to the addition of Avicel.  

How do Avicel RC-591 and Avicel CL-611 function as suspension aids?
Answer: In the presence of water and mild sheer, the powder particles swell and are then peptized, forming a dispersion of cellulose microcrystals. These microcrystals create a stable lattice structure for use in the formulation of suspensions and emulsions. 

What is the difference between Avicel RC-591 and Avicel CL-611 grades? 
Answer: These two products are produced under different conditions, which imparts a unique functionality to each. Avicel CL-611 is recommended for reconstituble suspensions. We recommend Avicel RC-591 for use in suspension products where shelf-life stability (e.g. no physical separation) is desired.

What levels of Avicel RC-591 and Avicel CL-611 do you recommended?
Answer: We recommend a starting use level of 1.2% for Avicel RC-591 and a starting use level of 2.6% for Avicel CL-611. These starting levels will create suspensions with viscosities of 72-168 cps and 50-118 cps, respectively. Exact use levels depend upon the desired viscosity for the final preparation and the nature of the active ingredient.  

What is the particle size of Avicel RC-591?
Answer: Avicel RC-591 (NF grade) is the compendial material "microcrystalline cellulose and carboxymethylcellulose sodium". Particle size for this product as purchased is monitored by Air Jet Sieve analysis and reported on each COA for the material. Since the product is typically used in pharmaceutical liquids, the particle size of the product supplied is not relevant in the processing or performance of the material, so particle size distribution is not performed on this material.  

How is the Avicel RC-591 prepared for use?
Answer: Avicel RC-591 requires the application of high shear dispersion in order to activate the material. This is generally as easy as processing with a rotor-stator type disperser, similar to a Silverson disperser in order to hydrate the material completely. 

My suspension containing Avicel RC-591 seems to separate into two layers and the viscosity decreases with time, why is that?
Answer: This is due to separation which occurs when Avicel RC-591 is not activated properly.  

What monograph does Avicel RC-591 meet?
Answer: Avicel RC-591 meets the NF Monograph “Microcrystalline Cellulose and Carboxymethylcellulose Sodium” and the BP monograph “Dispersible Cellulose.”

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