Nine binary mixtures of seven different methacrylic copolymer systems (Plas
toid(R) E 35 L (PLE) and Plastoid(R) L 50 (PLL); Eudragit(R) (Eu) NE, RL, R
S, L, S) were tested as components of monolayer patches containing miconazo
le. Only three mixtures (PLE:EuNE, PLE:EuRL and PLE:EuRS) were suitable for
the preparation of placebo matrices. Miconazole parches with good technolo
gical characteristics were obtained by using mixtures of PLE:EuNE and PLE:E
uRL. The in vitro miconazole release rate from the two patches and from the
patch prepared using only PLE were significantly different. The amounts of
drug released in 24 h were quits satisfactory. A mathematical model based
on capillary viscometry data was used for the evaluation of interactions be
tween copolymers. This was useful to predict and understand the mechanisms
related to the instability of the prepared mixture. The solubility paramete
rs of thr drug and of the matrix were also calculated. Miconazole release w
as faster when the difference between the solubility parameters of the matr
ix and of the drug was higher. A relationship between miconazole release ra
te and the difference of drug and matrix solubility parameters was found. T
herefore, the solubility parameter could be applied in formulation studies
of patches. (C) 1999 Elsevier Science B.V. All rights reserved.