In the process of compressing a tablet, of course there are problems, one of them is the weight variation. Usually, the range is still tolerable for large-sized tablets (diameter> 10 mm) was 3%, while for small tablet (diameter <7mm) is 5%. However, this specification ranges vary depending on the respective industry and the active ingredient of the drug. If the active ingredient is an extremely potent drug, in terms of the number of doses are very small (microgram scale) has a large effect, then the range specifications for tablet weight variation would be minimized.

Tablet weight variation in compressing process is not a trivial thing. Moreover, when affecting the uniformity of dosage units.

Tablet weight variation may be caused by:
  • Distribution at Hoover caused the vibration. So, small granule pushed, large granules will come out first, because there is a process of consolidation. Therefore, needs to be put a uniform granule size. So, before the compressing process begins, better evaluation the particle size distribution first.
  • The flow of granules is not good / not free-flowing granules
  • particle distribution is not normal, because the specific gravity is different, so that the flow is bad.
  • Keep the uniform of particle size distribution. Not too many fines and not too many granules. Granules with a large particle diameter which causes the resultant tablet has a variety of unsightly weight, while too fine granules which causes unsightly flow time.
  • lubricant or glidant less or not mixed evenly. 

How to overcome the weight variation of tablets:

1.Particle size distribution is uneven
Evaluate the particle size first. If too many fines, then you need to do is create a number of more granular. This case is commonly found on the direct compression process. This need not happen if are careful in choosing excipient for direct compression. The problem is excipient for direct compression is usually relatively more expensive.

If the active ingredient of the drug is stable to heat and humidity, then an easier way is to produce by wet granulation. Through granulation, drying and sifting, which formed granules can be more evenly. Critical points that need more attention is the moisture content and size of mesh used at the time of sifting.

If the active ingredients of drugs are not stable to heat and humid, then try to dry granulation, compaction with the compactor machine or slugging. Note the size of mesh used to sift.

What if large granule size is more? It is certainly easier to handle. You can resolve it by way of sifting the granules. Usually the size of mesh used to sift in the drying phase is the mesh 12. If the granules are still considered too large, you can sift it twice with 12 mesh sieve with a mesh or smaller, the mesh 20. Check again whether the particle size distribution was uneven.

2. Lubricant or glidant less or not mixed evenly.
To solve tablet weight variation, you also can add excipient Aerosil or colloidal Silicon Dioxide. This excipient was added to the external phase. The amount used is usually 1-2% of the total weight of the tablet. Mixing for 10-15 minutes. If you need to add lubricant (Magnesium Stearate) as much as 0.5% -1%. But, keep in mind lubricant is hydrophobic, may interfere with dissolution of tablets.

3. Specific gravity too different
This case often occurs in the manufacture of tablets that contain more than one type of granules. Two or more active ingredients each made in separate granules (usually because of incompatible), then at the time of compression into one, and coupled with the outer phase. Or two granules remain separate, but when compression using two different hopper, then compress into one tablet.

Two different granule must have the same specific gravity/ almost the same in order to avoid variations in weight.