Assessment of the Toxicologic Interaction of Diphenhydramine and Diazinon in the Invertebrate Daphnia magna

This paper will investigate a toxicologically relevant mixture interaction between the antihistamine diphenhydramine and the OP diazinon in a cladoceran model, D. magna. OPs function by irreversibly inhibiting AChE, the serine protease that hydrolyzes the neurotransmitter acetylcholine. This mode of action leads to increased extracellular levels of ACh which is toxic to pests, though it can be harmful and sometimes fatal to humans as well. The antihistamine diphenhydramine functions by reversibly binding to ACh receptors, which delays neurotransmission. In combination, these drugs have been shown to produce an inhibitory effect in mammals. This paper will study this mixture interaction in a cladoceran model and compare the interaction with the response predicted by the concentration addition model. Using individual acute toxicity tests and mixture assays, this study found a synergistic interaction between the two drugs, which could be attributed to the multiple modes of action of diphenhydramine or which may be the results of several limitations of this experiment.