| Tech Tip for Coating: The way you prepare a coating suspension has an impact on tablet quality! |
Coating suspensions are taken for granted. In pharmaceuticals the preformulated powder is received into the coating
area with very little thought about what is in it. Most people understand that it is a film forming material with a color. But
that powder is actually a complex blend of from 4 to 8 components that must be properly mixed, and kept properly
stirred, in order to achieve our goal.
And to do this we must first understand that “mixing” and “stirring” are not the same. We mix the powder into the vehicle,
almost always water, and then we keep it stirring during the lengthy coating process.
More importantly, it is best to use a high shear mixer to mix the powder into the water, then use a low shear device to
stir. An ideal combination would be a Ross Premax or a Triclover liquids/solids blender combined with a Lightnin mixer
for stirring during coating. For there is a great variation between companies on where and how suspensions are made
and where and how they are kept during the coating processes. There are almost as many exceptions as rules. The
important thing to remember is to clearly distinguish between the two objectives.
Here’s a picture of a suspension mixing tank. Notice that it has an internal high shear mixer engineered to eliminate
lumps, fish eyes (wet on the outside, dry on the inside) and sludge. Lumps and fish eyes can cause gun clogging in the
pan and are easily controlled with the use of a high shear mixer and an 80 mesh screen filter in the main solution line
out of the tank.
On the other hand, sludge is a thick, syrup like material that remains after the suspension has been pumped out. This is
actually under mixed powder that has fallen to the tank bottom virtually untouched. If you have seen this before, you’ve
overlooked a major problem. You actually combined syrup with orange juice and you tablets did not have anywhere
close to an optimized appearance. It couldn’t have, some of the critical material remained in the tank.
In the picture below we see a different tank. This is a suspension hold tank used to hold and stir the suspension during
coating.
One last item: May I use a single tank to both mix and hold the suspension? Of course and many companies employ this
practice. But if you must employ this practice, install and use two different classes of mixers to control suspension
manufacturing.
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| Solid Dosage Training, Inc. FREE TECHNICAL HELP Coating |
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