Publication Abstract

Malachite green and alternatives as therapeutic agents

D.J. Alderman

Malachite green is an arylmethane dye widely used to stain leather and acrylics which has been in use as a topical fungicide and antiprotozoal agent for more than 50 years. The carbinol 'pseudobase' of such dyes is lipophilic and occurs in ionic equilibrium with the dye form, dependant on the availability of hydroxyl ions. The lipophilic carbinol form is the form in which arylmethane dyes enter cells. The simple arylmethane dyes are effective biocides, killing susceptible cells by their action as irreversible poisons of respiratory enzymes within the mitochondria. A number of workers have suggested that malachite green is or may be a carcinogen or a teratogen. Whilst there is little scientific evidence available that supports these suggestions, it must be emphasized that malachite green is an old dye and little or no modern toxicological data exist on it nor is there significant commercial pressure for such work. Recent research demonstrated that malachite green is not only an effective topical antifungal and antiprotozoal, but is also an effective systemic antiprotozoal which can control proliferative kidney disease in rainbow trout. The corollary of this is that malachite green is absorbed by fish and that all fish tissues accumulate significant and fairly persistent residues of the dye. The use of malachite green on fish destined for human consumption is therefore contra-indicated unless a long withdrawal period is employed. Although formalin can and has been used instead of malachite green as a topical antifungal and antiprotozoal agent, it is less effective and it too presents significant toxicity problems for the user. In the marine environment, fungal infections in crustaceans which have often been treated with malachite green can now be controlled by trifuralin, but this is ineffective in fresh water and is not antiprotozoal. Despite extensive investigation, no alternatives to malachite green have been found which are as effective. Malachite green, with all its problems, is likely to be very difficult to replace.

Reference:

D.J. Alderman, 1992. Malachite green and alternatives as therapeutic agents. Special Publication of the European Aquaculture Society, 16: 235-244.