Question
Posted on: March 6 2013Does the yellow colouring due to an interaction between Clioquinol (Vioform) and ZnO cause an activity reduction? This yellow color I noticed in the clioquinol water paste of the TMF.
Answer
the emergence of the yellow colouring is done at a different speed according to the method of preparation used. If you add CL to an in-stock ZnO shake mixture, the initially white suspension is gradually becoming yellow. If you mix CL with the powder components during the preparation of the shake mixture, the suspension is immediately yellow after adding water. This reaction would also occur when CL is added to a suspension of ZnO in olive oil.
the discoloration can be avoided by replacing ZnO with TiO 2 . The different ways of responding between TiO 2 and ZnO can be deduced from the different place of Ti and Zn in the table of Mendeljev and also from their different solubility in diluted acids where ZnO is soluble in Dilute acids and TiO 2 not.
Despite the yellow colouring, the activity of CL is retained, as shown in the literature reference below.
Topical Antimicrobial Therapy: The efficacy of clioquinol-and zinc oxide preparations Fortschritte der Medizin; VOL: 100 (26); P. 1265-7, 1982A comparison between the Antimicrobi ë le activity of ZnO and TiO 2 preparations with CL could not be found in the literature.Clioquinol-and zinc oxide preparations were tested in vitro in order to investigate their bactericidal and bacteriostatic efficacy against strains of Staphylococcus aureus, E. coli, Pseudomonas as well as against the fungi Candida albicans and Trichophyton rubrum. The results show that there was both a bacteriostatic and a bacteriocidal effect of clioquinol except against Pseudomonas. In spite of some suggestions in the literature our results confirm that the efficacy of clioquinol is not impaired if combined with zinc oxide. The use of this well tolerated preparation is recommended in the treatment of infectious dermatoses even today.