[Influence of viscosity on drug release from ointments, creams, gels and emulsions]

The authors studied the drug release from high number of water-free ointments, creams, emulsions and hydrogels. They targeted to find correlation between the viscosity of these pharmaceutical forms and their drug release. Neutral oil was the lipophilic phase of emulsions, the emulsifiers were from Tween and Tagat series. The creams tested consisted of ESMA ointment, Teginacid and/or Softisan emulsifiers and water in 60-80 w/w%. The drug release from Eudispert, methyl-cellulose and hydroxy-ethylcellulose gels was studied. The applied active ingredients were as follows: griseofulvin, sulfadimidine, salicylic acid and ephedrine hydrochloride. Relevant literature suggest a reciprocal correlation between the viscosity of ointments and the quantity of the released drugs. The authors confirmed the general validity of this correlation in case of the following preconditions: if the solubility and distribution of drug do not change along with the change of viscosity there is reciprocal ratio between viscosity and the quantity of drug released. This reciprocal correlation prevails only in a small range of viscosity, that is in systems resembling Newton's liquids. In cases of ointments and gels of higher viscosity a reciprocal relationship exists between the logarithm of viscosity and the quantity of drugs released.