Response of dogs to subcutaneous injections of various concentrations of propylene glycol with water.

Each of 85 dogs was injected, subcutaneously, with 5 different mixtures of propylene glycol (PG) and aqueous vehicles. Each dog was observed for immediate (within 15 minutes) and delayed (at 24, 48, and 72 hours) reactions. The reactions were classified as none, mild, moderate, and severe for the different observation periods. The study indicated that a mixture containing between 20% and 50% PG caused the fewest immediate reactions and that the number of delayed reactions increased as the proportion of PG in the solutions increased. Viscosity of the mixture also should be considered when selecting a vehicle.