Methods of evaluation of release of carbon dioxide from effervescent suppositories

Two different test methods were studied for the evaluation of release profiles of carbon dioxide, CO2, from effervescent suppositories. Three lots of commercial suppositories containing sodium bicarbonate and anhydrous sodium dihydrogen phosphate were used. The volume of CO2 released from these suppositories in normal saline with or without polysorbate 80 as a medium was measured with a gas burette. In the measurement performed using the apparatus without stirring, method 1, only 60% of CO2 was released from the suppositories in the medium without polysorbate 80. In this measurement, a native release profile was detected because the medium was not stirred. In the case with stirring, however, method 2, 100% was released from those suppositories in the medium containing 1% polysorbate 80 with comparatively low standard deviations. These findings indicate that method 1 is most beneficial for a test comparing the effects of various factors such as additives and melting points on the release profiles of CO2 from the effervescent suppositories. However, this method is not practical for quality control of formulations because of the incomplete release of CO2; method 2, in contrast, is useful because of its complete release and low standard deviations. These results suggest that methods 1 and 2 for release tests of CO2 are most applicable to the early and late formulation studies of effervescent suppositories, respectively.