AIMTo study the erosion behaviour during dissolution of matrices using different molecular weight polyethylene oxide (PEO) as hydrophilic polymer.

METHODSPEO hydrophilic matrix tablets with no added drug and excipients were prepared by direct compression method. The erosion rates of matrices comprised of pure or blending PEO polymers were evaluated in distilled water at (37 +/- 0.5) degrees C with rotating rate of 50 r x min(-1). The relationship between PEO molecular weight and erosion rate of matrices was investigated by experimental and mathematical model methods.

RESULTSThe gravimetric erosion experimental results indicated that the power-law relationship which relates the polymer erosion rate and weight average molecular weight: k infinity (M(w)) -1.30 4 was proved to have great potential utility in predicting the degree of polymer erosion of matrices comprised of either intermediate molecular weight (97. 98 x 10(4) - 553. 36 x 10(4)) or blends of lower and higher molecular weight polymers. Based on the semiempirical equation for mass transfer rate: Jp = (fp < Dp > (2/3) v (-1/6) omega (1/2)) C(p,dis), a theoretical mathematic model was developed for describing the relationship between PEO erosion rate and PEO weight average molecular weight: Jp infinity M(-1.241), where the exponent of -1. 241 was very close to the exponent of - 1. 130 4 obtained from practical determination.

CONCLUSIONPEO was proved to be a good candidate of hydrophilic polymer and appeared to have great potential for controlled release applications. The mathematic model presented together with the utilization of the erosion behaviour discussed in our study could provide a guide line to predict the degree of polymer erosion for other intermediate polymer grades and / or mixture of the polymers utilized in this study, which could play an active role in designing PEO hydrophilic sustained delivery systems.