Abstract
The rheological properties of Carbomer and Polycarbophil gels were studied in relation to pH, Carbomer concentration and brand, temperature, and dispersal medium composition. The study results permit rational selection of Carbomers as gel-forming agents. Gel formation occurring on neutralization of Carbomer with alkali did not lead to any increase in the viscosity of the gel dispersal medium; spin probes dissolved in it remained in the state of rapid isotropic rotation at the micro level, which provides conditions for rapid and complete release of drugs dissolved in these gels. In contrast to this, the rotational diffusion correlation time (τ-1) of the probe 4-amino-TEMPO in gels passed through a maximum at pH 7.1 – 8.7, which appeared to be due to interaction of the cation formed by protonation of the amino group of this spin probe with several neighboring carboxylate-anions of the Carbomer. Increases in temperature weakened this effect, while ethanol and N-methylpyrrolidone in the gel increased it. This interaction could decrease the release of some drugs, with decreases or prolongation of the efficacy of their pharmacological actions.
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