A MULTIPLANT PROCESS CAPABILITY STUDY OF THE PERCENT ASH AND SPECIFIC GRAVITY PROPERTIES OF ELASTOMERIC PHARMACEUTICAL CLOSURES

Percent ash and specific gravity specifications and specification tolerance intervals for individual elastomeric pharmaceutical closure compounds have been empirically established for several decades. This work determines the process capability, defined as the ratio of the tolerance interval to six standard deviations about the mean, of a multiplant manufacturer of elastomeric closures. Lot testing data of percent ash and specific gravity results on twenty broadly representative elastomeric compounds was tested statistically for patterns of non-randomness, control-charted, and subjected to an analysis of variance procedure to determine if interplant differences in mean values exist. Some evidence of non-randomness appeared, a few isolated points outside the three standard deviation control limits occurred, and several compounds exhibited statistically significant but practically non-significant interplant differences in means. Interplant homogeneity of variances was demonstrated. Unweighted pooled standard deviations were used to estimate the multiplant process standard deviations. Percent ash process capabilities ranged from 0.75 to 3.92 with nineteen of the twenty compounds greater than 1.00. The lone compound whose process capability was less than 1.00 was produced infrequently at a very low volume of production during the time period of this study. It was concluded that the multiplant process is "capable" with respect to the percent ash specifications. Specific gravity process capabilities ranged from 0.83 to 2.78 with eighteen of the twenty compounds greater than 1.00. The mixing procedures of the two compounds whose process capabilities are less than 1.00 need to be adjusted to reduce the variances of their specific gravity properties. It was concluded that the multiplant process is generally "capable" with respect to specific gravity specifications.