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 movement in Hydroxypropylmethylcellulose (HPMC) matrices which contain both a freely and a poorly soluble drug, respectively, is described. A new method based on the measurement of backscattered ultrasound signals has been developed for characterizing advancement of eroding front. The advantage of the ultrasound method is the possibility of continuous measurements. Our investigations indicate that both methods achieve nearly the same result. Matrices with pholedrine sulphate showed greater movements of the eroding front compared to matrices with chloramphenicol, whereas the movement of the swelling front was almost the same in each case. The drug release is dependent on the solubility of the drug, therefore the diffusion of the drug through the gel and therefore the position of the diffusion front in the gelling zone can be considered a possible descriptor of drug release from HPMC matrices.