Abstract

Increasing the penetration rates of active substances from transdermal preparations to skin is a major goal for the pharmacy technologists. Higher concentration of the active substance in the skin is commonly associated with higher treatment quality. The aim of this study was to model an optimal pharmaceutical iontophoretic delivery form and to examine the dependency of its quality and stability on different parameters (that is, polymer type and concentration used for formulation, the viscosity of the vehicle, and its electrical conductivity). Gels have been intended to be used for 5-aminolevulinic acid (5-ALA) incorporation. The optimization of the vehicles has been performed without 5-ALA insertion due to its high price and very large standard concentration according to dermatologic protocols; but the gels have been evaluated accordingly to 5-ALA chemical properties. Different concentrations (0.25 to 10%) of four polymers (carbopol (CP), methylcellulose (MC), hypromellose (HM), and hydroxypropylcellulose (HPC)) have been selected for the formulations, and they produced wide range of dynamic viscosity (1.5 to 10000 mPa×cm). The highest shear viscosity has been measured in CP gels; dynamic viscosity was the highest in MC gels. 1000 to 5000 mPa×s was identified as the optimal dynamic viscosity for the iontophoretic gels. The following polymer concentrations have been singled out as optimal ones: 1% for carbopol, 4% for methylcellulose, and 3% for hypromellose. PH values of 5 and 7 have been identified as the most suitable for 5-ALA incorporation.

Key words: Gel, iontophoresis, viscosity, conductivity, rheology.