title: Estimation of the percolation thresholds in ternary lobenzarit disodium-dextran-HPMC hydrophilic matrices tablets: effects of initial porosity.
abstract: The aim of this work is to estimate the excipient percolation threshold for a new combined matrix native dextran (DT), series B110-1-2 (Mw 2 x 10(6)): HPMC K4M CR: lobenzarit disodium (LBD) system and demonstrate the advantages of this ternary system with respect to previously reported binary dextran:LBD and HPMC:LBD tablets. The formulations studied were prepared with different amounts of excipient (DT:HPMC, 4:1 (wt/wt) for all tablets and relative polymer/drug particle size of 4.17) in the range of 10-70% (wt/wt). Dissolution studies were carried out using the paddle method (100 rpm) and one face water uptake measurements were performed using a modified Enslin apparatus. The Higuchi's models as well as the non-linear regression were employed as empiric methods to study the released data. Values of diffusion exponent 0.588<n<0.784 (Korsmeyer equation) for dissolution profile and water uptake mechanism 0.715<n<0.960 (Davidson and Peppas equation) suggests anomalous or complex mechanisms in all cases. The critical points in ternary tablets were reduced from 44.75% (v/v) of excipient (correspond to purely native dextran) to 22.34% (v/v) (corresponding to mixture native dextran:HPMC, 4:1, wt/wt). The initial porosity (IP) of hydrophilic matrices above the values of 20% has an important influence on the percolation threshold as well as on establishment of the gel barrier responsible for the controlled release from the DT:HPMC:LBD tablets.
authors: Faculty of Pharmacy, University of Havana, Cuba. eddy02cu@yahoo.es
authors: Eddy
authors: E
authors: Castellanos Gil
authors: Antonio
authors: A
authors: Iraizoz Colarte
authors: Bernard
authors: B
authors: Bataille
authors: Fabien
authors: F
authors: Brouillet
authors: Isidoro
authors: I
authors: Caraballo
mesh_terms: D003911:Dextrans / Q000737:chemistry* / Q000493:pharmacokinetics; D007785:Lactose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D008747:Methylcellulose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D016062:Porosity; D013607:Tablets; D013678:Technology, Pharmaceutical / Q000379:methods* / Q000706:statistics & numerical data; D062367:ortho-Aminobenzoates / Q000737:chemistry* / Q000493:pharmacokinetics
chemical_list: D003911:Dextrans; D013607:Tablets; C509290:hydroxypropylmethylcellulose-lactose matrix; D062367:ortho-Aminobenzoates; D008747:Methylcellulose; C015735:lobenzarit; D007785:Lactose