Effects of bases and additives on release of carbon dioxide from effervescent suppositories

For the formulation of effervescent containing sodium bicarbonate and anhydrous sodium dihydrogen phosphate, the effects of bases and additives on the release profile of carbon dioxide, CO2, from the suppositories were studied by an in vitro release test using a gas burette. The suppository bases employed were Witepsol H-15, W-35 and E-85, and the additives were Aerosil 200 and soybean lecithin. The melting points and viscosities of the suppositories were also measured to interpret the CO2 release profiles. The rate and amount of CO2 released from suppositories prepared with bases having different melting points and hydroxyl values decreased with increasing melting point and decreasing hydroxyl value. The addition of Aerosil 200 to the suppository bases considerably reduced the rate and amount of CO2 released owing to the increasing viscosity of the melted bases, while the addition of soybean lecithin to those bases increased the rate and amount of CO2 released because of the improved wettability. Thus, the release profiles of CO2 from the effervescent suppositories were considerably influenced by the hydroxyl values related to the contents of mono- and di-glycerides, the melting points of the bases, Aerosil 200 and soybean lecithin. This suggests that the rate and amount of CO2 released from the suppositories can be freely controlled by the combination of these various factors.