Sources of variation during collaborative evaluation of in vitro dissolution tests for two solid preparations.

Collaborative in vitro dissolution tests on a sample of commercial tolbutamide tablets and a sample of oxytetracycline capsules were carried out in eight laboratories. The two preparations tested showed differences between the products in release characteristics, particularly in the distintegration phase. This may have caused the difference in the pattern of variance in the two trials. In the case of tolbutamine tablets the value of the repeatability standard deviation was small, and therefore the major contribution to the variance was in the difference between laboratories. With oxytetracycline capsules the major contribution of the variance lies in the random errors common to all laboratories (i.e. the within-laboratory variance). One major source of inter-laboratory viance was identified as the level of vibration at the side of the dissolution flask. Another source of variation was found to be due to using a stated extinction coefficient instead of comparing the absorbances of the samples to those of a solution of a reference substance.