20% MP as the plasticizer. Drug release from coated beads was highly dependent on the relative humidity. A decrease in drug release rate was observed from coated beads stored at the higher relative humidity. These results are in agree- ment with the ®ndings of Amigi and Moes who reported that drug release rates from beads coated with Eudragitw RS 30 D and plasticized with triethyl citrate were signi®cantly reduced when the coated beads were stored at higher levels of relative humidity [3].
Coated beads equilibrated at 0% RH for 5 weeks were then stored at 84% RH and the data are presented in Fig. 6. The drug dissolution rate from the coated beads decreased as the storage time at 84% RH was increased. These ®ndings were, as shown in Table 1, associated with a corresponding