Evaluation of floating and sticking extended release delivery systems: an unconventional dissolution test

The extent to which hydrophilic matrix tablets with a propensity to stick t o the dissolution apparatus and/or float are susceptible to variations in h ydrodynamic conditions during dissolution testing was investigated. Further more the usefulness of simple alternatives to the current compendial tests is examined. Swellable hydrocolloid (guar) matrix tablets containing verapa mil HCl were evaluated using USP dissolution apparatus I and II. Two additi onal configurations where an additional single ring and mesh device or a do uble mesh device was located below the paddle in the dissolution vessel wer e also evaluated. Tablets were placed on top of the single mesh device or i n the compartment formed by the two mesh surfaces of the double mesh device . In all cases near linear (n greater than or equal to 0.82) release profil es were observed. When using apparatus I it was observed that the highly sw ellable tablets were fully constricted by the basket within 5-7 h. This pre vented further independent movement and unimpeded swelling and coincided wi th a departure from linear release and increased variability (S.D.less than or equal to 9.5%). Under standard apparatus II conditions two out of three tablets adhered to the bottom of the dissolution vessel for the duration o f the experiment. Consequently their release profiles differed markedly fro m those obtained under apparatus I conditions (similarity factor, f(2)=30.5 ) with the release rate being approximately half of that obtained under app aratus I conditions. Adhesion to the dissolution vessel was also observed w hen paddle speed was doubled to 100 rpm, thus again resulting in large vari ability (S.D.less than or equal to 34%). Whilst the averaged single and dou ble mesh configuration profiles were similar to the apparatus I profile (f( 2)=57.36 and 61.38, respectively), large variability (S.D.less than or equa l to 11%) occurred with the single mesh configuration due to floating and r andom adhesion of tablets to the paddle or sampling tubes. Almost superimpo sable profiles were obtained for the individual tablets (S.D.<3%) when the tablets were located in the compartment formed by the double mesh device. U se of a double mesh device may therefore provide an alternative to current compendial dissolution methods when the reliable determination of the true release kinetics of floating and sticking delivery systems is desired. (C) 2000 Elsevier Science B.V. All rights reserved.