Blending Basics for Tablet Making
Blending in solid dose manufacturing has two objectives; 1) To achieve blend uniformity and 2) to distribute the lubricant. In (objective 1) the blend step(s) are designed to achieve homogeneity of all components prior to the final blend of the lubricant (objective 2). The challenge is that there is no such thing as a perfect blend. Blending is like shuffling a deck of playing cards; there is just no such thing as a perfect shuffle. As with shuffling playing cards, blending powders is even more of a challenge due to particle size, moisture content, structure, bulk density and flow characteristics. The bottom line is that blending techniques for tablet making must produce predictable and repeatable results to achieve content uniformity and proper function. The first step in achieving predictable results in a blend is to introduce the proper particle profile within a range; between 40 – 180 mesh for most oral solid dosages. We do not want any particles larger than 20 mesh and try hard to limit the percentage of fines to less than 20% smaller than 200 mesh. The next step is to complete pre-blending steps in a carefully planned order of addition. In other words we need to blend powders with a strategy. Many formulators blend actives and then excipients, others add based on percentages. Over the years I have found that the best success is to know your objective. Simply realize the goal to deliver an active ingredient that holds together, produces predictable results, disintegrates correctly and dissolves when you want it to, only after having sustained the correct shelf life…so what could be the problem? The best thing is an example of an existing formula; say I have a dry granular formula and a number of overly fine waxy actives, along with a flow agent, bulk agent, and a binder. My first question is how does it flow, then how does it compress and the how does it eject, then how does it disintegrate, dissolve and stability and shelf life. I would use the waxy fine particles to coat the larger dry particles to aid compressibility. Then I would add the binder and bulk agents and test between steps for proper parameters of the deleveloping tablet. Too many formulas are old recipes without rhyme or reason. Many formulas are excellent but are not blended correctly; the key to a successful formula is the order of addition. Since each formula is different there are many factors to be considered for each and every formula. When all ingredients are dumped into the blender, optimization is rarely achieved and many times flow, compression and ejection are put into jeopardy. The key is proper addition including the lubricant. Add the lubricant last, by itself; never blend it with anything else, and only blend for a short duration. Under blending a lubricant is better than over blending it.
I hope this helps….any questions or comments please let us know.
Posted by Mike on June 29th, 2009 :: Filed under Blending, Tableting
Tags :: Blend Steps, Blend Uniformity, Blending, Blending Powders, Blending Techniques, compress, eject, Flow, Formulas, Homogeneity, Lubricant, Solid Dose Manufacturing, Waxy fine Particles