Problems associated with the use of merthiolate as a preservative in anti-lymphocytic globulin

The cytotoxic properties of 2 anti-lymphocytic globulin (ALG) preparations were investigated in vitro by measuring the release of 51Cr from labelled human peripheral blood mononuclear cells, tonsil lymphocytes and Chang cells, incubated with different concentrations of ALG. One of the ALG preparations showed non-selective cytotoxicity in the absence of complement. Evidence was obtained to suggest that this effect was due to merthiolate (sodium ethylmercurithiosalicylate) which had been added to the ALG as a preservative during manufacture. The mercury concentration in the ALG was found to be greater than that stated by the manufacturers. It is conceivable that the clinical use of such as ALG preparation might lead to mercury accumulation in the tissues, with resulting toxic effects. The whole question of the use of merthiolate in the preparation of sera for administration to human subjects needs to be reconsidered.