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High consumption of drugs, combined with their presence in the environment, raises concerns about its consequences. Even though researches are often engaged in analyzing substances separately, that is not the environmental reality. Therefore, the aim of this study was to investigate the acute toxicity of the pharmaceuticals simvastatin, metformin, omeprazole and diazepam, and all possible mixtures between them, to the organism Aliivibrio fischeri, verifying possible synergistic or antagonistic effects and assessing byproducts formation. In terms of individual toxicity, omeprazole is the most toxic of the active ingredients, followed by simvastatin, diazepam and, finally, metformin. When the toxicity of mixtures was tested, synergism, antagonism and hormesis were perceived, most probably generated due to byproducts formation. Moreover, it was observed that even when compounds are at concentrations below the non-observed effect concentration (NOEC), there may be toxicity to the mixture. Hence, this work points to the urgent need for more studies involving mixtures, since chemicals are subject to interactions and modifications, can mix, and potentiate or nullify the toxic effect of each other.

Considerable quantities of different classes of drugs are consumed annually worldwide. These drugs, once disposed, often remain stable, even after conventional or advanced treatments. Although there have been a number of studies on the potential harm caused by drugs when released into the environment, few studies have investigated the toxicity of pharmaceutical excipients. In the present study, the acute toxicity of 30 drugs was tested to Aliivibrio fischeri. Ten different active ingredients were investigated, each in three distinct formulations: generic, similar and reference (brand drug). The aim of the study was to evaluate the harmful potential of drugs frequently sold in drugstores and to assess the contribution of excipients towards the observed acute toxicity. Within the 10 drugs evaluated, only one, dexchlorpheniramine maleate, was not toxic in any formulation. The toxicities of the three formulations were often different, even though the active ingredient has been the same. For some drugs, such as diazepam, glibenclamide, metformin, nimesulide, hydrochlorothiazide and simvastatin, only one or two of the three formulations tested were toxic to A. fischeri. These results highlight the toxicological potential of drug excipients, but not exclusively the toxicity of the active ingredients.