The intrinsic dissolution rate is defined as the dissolution rate of pure substances under the condition of constant surface area, agitation-stirring speed, pH and ionic-strength of the dissolution medium.
The knowledge of intrinsic dissolution rate is vital in screening new drug candidates as it can help optimize the physiological effectiveness of new dosage forms. Distek has improved the performance and reliability of the rotating cylinder or “wood apparatus” with the paddle over stationary disk intrinsic apparatus. This is available in two configurations; standard for use with 1L vessel and mini for use with 100/200 ml vessels. The Distek design avoids the formation of air bubbles on the surface of the product and eliminates the potential of product “slippage” as can be the case with the wood apparatus.
The Distek standard and mini intrinsic apparatus consists of steel punch, die, and base plate (fig. A).
Test material is placed in the 0.8 cm diameter die cavity (optional cavity sizes are available) and the punch is inserted. The punch, die and press plate are placed in a laboratory press and kept under 2000 psi for 4-5 minutes. The press plate is disconnected from the die to expose a compact pellet of .5 cm2 surface area.
A Viton gasket is placed around the threaded shoulder of the die and a polypropylene plastic cap is screwed onto the threads. The assembly is then immersed, pellet side up, in the bottom of a flat dissolution vessel containing 900ml of dissolution medium at 37C. The paddle blade is positioned 6mm above the surface of the pellet and rotated at 50 rpm.
See USP 30-NF 25 General Chapter <1087> page 531 for more details.