Evaluation of crushing strength of blank tablets (Y
PEG has the most significant effect (p < 0.005) on the blank tablets' crushing strength. All the batches exhibiting hardness >100 N showed the presence of PEG.
PEG alone, however, may not be a very good binder. The binder may have occupied the voids between the particles, decreasing
the porosity of the tablet. Thus the addition of binder with a low yield-pressure value and a relatively small elastic-recovery
value (e.g., PEG and PVP) results in tablets of low porosity and high tensile strength (22). The other excipients also tended
to increase the hardness of the blank tablet, except acacia.
Evaluation of tablets containing acetaminophen (Y
Table IV shows that guar gum had the most significant effect on the crushing strength of the tablets containing acetaminophen.
HPMC, acacia, and silicon dioxide increased the hardness of acetaminophen-containing tablets, and PEG and starch decreased
the hardness of the tablets. Acetaminophen is a poorly compressible drug; therefore, the filler–binder must be robust enough
to take up this poorly compressible material and still retain its compressibility. The interaction with the other components
of the system might have caused the lower values of coefficients of PEG and starch in the equation for the calculation of
CSP. The directly compressible diluent thus behaves in a different manner in presence of acetaminophen. Many researchers have
emphasized the fact that the directly compressible diluent behaves differently in presence of drugs; therefore, it is necessary
to choose a right directly compressible diluent for a particular drug (23).
The Placket-Burman design indicated that starch, silicon dioxide, and HPMC had pronounced effect on the compressibility index.
Starch was a common ingredient affecting the angle of repose and compressibility index. The results of crushing strength indicate
that guar gum and polyethylene glycol had predominant effects on the crushing strength of the blank tablets. Guar gum was
a common factor affecting the crushing strength of the blank tablets and that of acetaminophen-containing tablets. Hence the
23 factorial design was applied, with starch and guar gum as constant excipients along with the lactose and DCP and hydroxypropyl
methylcellulose (A), silicon dioxide (B), and polyethylene glycol (C) were varied at two levels in accordance with the data
shown in Table III.
Results from the analysis of data obtained for each response parameter were fitted into a linear polynomial equation of the
Y = b
0 + aA + bB + cC + abAB + bcBC + caCA + abcABC
in which Y is the level of response parameter, b
0 is the arithmetic average of eight response and a, b, c, ab, bc, ca, and abc are the estimated coefficients for the factors A, B, C and the interaction terms AB, BC, CA and ABC, respectively. ANOVA was performed to eliminate the non-significant terms from the equation.
Table V: Regression analysis data for the parameters evaluated as per 23 factorial design indicating the values of coefficients for the factors and their interactive terms