THE USE OF ULTRASOUND AND PENETROMETER TO CHARACTERIZE THE ADVANCEMENT OF SWELLING AND ERODING FRONTS IN HPMC MATRICES

The determination of gel layer thickness and the velocity of front mov ement in Hydroxypropylmethylcellulose (HPMC) matrices which contain bo th a freely and a poorly soluble drug, respectively, is described. A n ew method based on the measurement of backscattered ultrasound signals has been developed for characterizing advancement of eroding front. T he advantage of the ultrasound method is the possibility of continuous measurements. Our investigations indicate that both methods achieve n early the same result. Matrices with pholedrine sulphate showed greate r movements of the eroding front compared to matrices with chloramphen icol, whereas the movement of the swelling front was almost the same i n each case. The drug release is dependent on the solubility of the dr ug, therefore the diffusion of the drug through the gel and therefore the position of the diffusion front in the gelling zone can be conside red a possible descriptor of drug release from HPMC matrices. (C) 1998 Elsevier Science B.V. All rights reserved.