Translocation of drug particles in HPMC matrix gel layer: effect of drug solubility and influence on release rate

The aim of this wort; was to study the release mechanisms of drugs having d ifferent solubility (buflomedil pyridoxalphosphate 65%, sodium didofenac 3. 1%, nitrofutantoin 0.02% w/v,) from hydroxypropyl methylcellulose (HPMC) ma trices by concomitantly studying swelling, diffusion and erosion fronts mov ement and drug delivery. The main goal was to clarify the role played by po lymer swelling in drug transport. The results showed that the rate and amou nt of drug released from swellable matrices was dependent not only from dru gs dissolution and diffusion but also from solid drug translocation in the gel due to polymer swelling. In fact, as drug solubility decreased, the slo wer drug dissolution rate in the gel layer allowed drug particles to be tra nsported close to the matrix erosion front. The presence of solid particles in the gel reduced the swelling and the entanglement of polymer chains and affected the resistance of gel towards erosion. As a consequence, the matr ix became more erodible. The erosive delivery accelerated after the matrix had been completely transformed into the rubbery state, particularly when a considerable amount of solid drug particles remained in the gel phase. (C) 2001 Elsevier Science B.V, All rights reserved.