PubMed · 15977973
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Virendra Rambiritch, Poobalan Naidoo. 2005. Gliclazide modified release.. https://doi.org/10.2165/00003495-200565100-00009
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Two matrix theophylline tablets with different release mechanisms were compared. Tablet A was a swelling/disintegration-type wax matrix made of hydrophobic wax granules, consisting of stearic acid, hydrogenated oil and glycerol esters of fatty acids, and hydrophilic polymer granules composed primarily of hydroxypropyl methylcellulose (HPMC). We named Tablet A the cluster tablet. Tablet B was a gel matrix made of hydrophobic ethylcellulose granules, consisting of ethylcellulose and hydrogenated oil, and hydrophilic polymer granules consisting of HPMC and hydroxylpropylmethylcellulose acetate succinate (HPMCAS). The formulations were screened in vitro according to their dissolution characteristics. The drug release from each preparation was analyzed using release kinetics theories. In Tablet A, the value of the exponent(n) representing the apparent diffusion mechanism determined from the Korsmeyer-Peppas model equation was about 0.6 and was unlikely to be affected by the rotation speed. In Tablet B, the value of the exponent(n) by the Korsmeyer-Peppas model equation changed with the paddle rotation speed. These results suggested that the drug release mechanism of Tablet B is greatly affected by the extent of physical force in the gastrointestinal tract.
Zeolites can accommodate a considerable amount of occluded salt such as NH4NO3, which can serve as a good source of slow-release plant nutrient. This study evaluates the kinetics of ion release from NH4NO3-occluded Na-P1 (N-NaP) using a simulated soil solution and deionized water as leaching solutions. The patterns of ion releases were examined as a function of leaching time under both static and continuous-flow conditions for more than one month. Releases of both NH4+ and NO3- from N-NaP were found to be slow and steady under both the above conditions. The soil solution affected the release of NH4+ and NO3- differently, while deionized water released nearly the same equivalents of these ions. This clearly indicates that ion release from salt-occluded zeolite involves two different reactions, cation exchange and dissolution. The kinetics of ion release from occluded NH4NO3 under static condition was best described by the standard Elovich model while the power function model best expressed these under continuous-flow condition. The initial ion release patterns under both conditions exhibited considerable deviation from the simulated models, probably as a result of the presence of hydrated occluded NH4NO3. Flow condition and the presence of electrolytes in leaching solution affected the release kinetics significantly. Release of occluded NH4NO3 was delayed by the presence of the NH4NO3 coated on zeolite crystals. These results indicate that the ion release property of occluded salt could be predicted and controlled. This study clearly shows that NH4NO3-occluded zeolites could be developed as slow release fertilizers.