Pharmaceutical Manufacturing Handbook: Production and

thus reducing a potential variation of weight, compression should be conducted
within a narrow range of the powder or granulate product in the hopper.
The fi ll cam is another factor that can have a profound effect on tablet weight.
The choice of an adequate fi ll cam regarding some characteristics of the powder or
granulate product allows the die cavity to be properly overfi lled. Usually, in order
to maintain consistent tablet weight during compression, it is recommended to
overfi ll the cam by 10 – 30% of its volume. Basically, any tablet press part that is
ultimately related to the powder product fl ow can have a mild or profound impact
on weight control. It is important to remember that the scraper blade tends to
become worn by die table rotation and powder product abrasion. Therefore, periodic
inspection of its condition and replacement are recommended. Nevertheless,
the scraper blade proper condition is important but also its adjustment since if it is
not set up correctly, powder product may accumulate on the die table, leading to
problems with weight control.
Tablet hardness variation is intimately related to weight variation and, accordingly,
to the infl uence of compression variables such as dwell time, tablet thickness,
and working length of the punches. Thus, to solve a hardness variation, consistency
of the tablet weight must be checked fi rst. If the predefi ned weight is achieved but
hardness is out of limits, then precompression and compression forces should be
adjusted while keeping tablet thickness within target limits. Although dwell time
might be a source of hardness variation, adjustment of this parameter may be detrimental
to the whole process since the compression rate is slowed. Occasionally,
when the tablet weight target is kept within limits but hardness varies, the problem
may be due to the formulation. As mentioned previously, the correct use of punches
and dies is of paramount importance and periodic inspection is mandatory in order
to ensure the compression process has not been compromised. So, when it becomes
hard to achieve tablet hardness, it is recommended to fi rst verify tablet weight and
thickness consistency and then try to adjust the precompression. The choice to
increase the tablet weight even if it is within limits or to reduce the tablet press
speed is not convenient and should be used only when there are no more options.
REFERENCES
REFERENCES 1161
1. Ç elik , M. ( 1994 ), Compaction of multiparticulate oral dosage forms , in Ghebre - Sellassier ,
I. , Ed., Multiparticulate Oral Drug Delivery , Marcel Dekker , New York , pp. 181 – 216 .
2. Parrot , E. ( 1990 ), Compression , in Lieberman , H. L. , and Schwartz , J. B. , Eds., Pharmaceutical
Dosage Form , 2nd ed., Marcel Dekker , New York , pp. 201 – 244 .
3. Shlieout , G. , Wiese , M. , and Zessin , G. ( 1999 ), A new method to evaluate the consolidation
behavior of pharmaceutical materials by using the Fraser - Suzuki function , Drug. Dev. Ind.
Pharm. , 25 ( 1 ), 29 – 36 .
4. Mohammed , H. , Briscoe , B. J. , and Pitt , K. G. ( 2006 ), A study on the coherence of compacted
binary composites of microcrystalline cellulose and paracetamol , Eur. J. Pharm.
Biopharm. , 63 ( 1 ), 19 – 25 .
5. Leuenberger , H. , and Leu , R. ( 1992 ), Formation of a tablet: A site and bond percolation
phenomenon , J. Pharm. Sci. , 81 ( 10 ), 976 – 982 .
6. Khossravi , D. , and Morehead , W. T. ( 1997 ), Consolidation mechanisms of pharmaceutical
solids: A multi - compression cycle approach , Pharm. Res. , 14 ( 8 ), 1039 – 1045 .