Studies on phenol and chinosol used as preservatives in tuberculin PPD solutions.

Phenol and chinosol (8-hydroxyquinoline sulfate), used extensively in commercial preparations of tuberculin PPD, were compared for their antimicrobial activity and their stability during storage.The antimicrobial activity of phenol (0.3%) was found to be much greater and to cover a wider spectrum of organisms than chinosol (0.01%). In ampoules, the phenol content of a tuberculin PPD solution did not change during 24 months of storage at 5 degrees C or 37 degrees C while the chinosol content decreased approximately 30% in 24 months of storage at 5 degrees C. Tuberculin solution stored in rubber-stoppered vials, lost less phenol than chinosol.Chinosol formed crystalline deposits during storage as a result of the reaction of 8-hydroxyquinoline with traces of metals present in the tuberculin solution; phenol did not form any precipitate.On the basis of its wider antimicrobial spectrum and greater stability, the authors suggest that phenol rather than chinosol should be used as a preservative in tuberculin PPD solutions.