A modified Franz diffusion cell for simultaneous assessment of drug release and washability of mucoadhesive gels

A modified Franz cell is proposed to simultaneously measure the amount of drug diffused from semisolid preparations into the receptor chamber and the amount washed away by a tangential buffer stream. Four gels containing acyclovir as model drug and based on hydrophilic polymers (sodium carboxymethylcellulose, methylvinyl ether/maleic anhydride copolymer, methacrylic acid/methacrylic acid methylester copolymer, and polyacrylic acid) were tested. The drug release profiles to the receptor chamber of a standard Franz cell apparatus were obtained and compared to the profiles obtained with the modified apparatus at two buffer stream rates (1.0 and 0.3 ml/min). Same significant differences were observed between the wash-away profiles obtained with the two buffer stream rates. At both flux rates the amount of drug washed away was quite high, and in turn, the drug release profiles to the receptor chamber were lower with respect to those obtained with the standard Franz cell test. The importance of this phenomenon was not the same for all of the polymers: the polyacrylic acid sample, because of the presence of slight crosslinking, was less sensitive to wash away. For all of the other samples, when 1.0 ml/min tangential stream was used, the amount of drug released to the receptor chamber was significantly lower with respect to the standard method. With 0.3 ml/min buffer stream, some significant reduction in release amounts could be observed for the methacrylic acid/methacrylic acid methylester copolymer sample only, which was also the most erodible sample. The method proposed appears suitable to differentiate the examined samples for sensitivity to the washing effect.