mercurial diuretic, any one of several diuretic agents that contain mercury in an organic chemical form. The principal use for the drugs is in treating edema of cardiac origin, ascites associated with cirrhosis, or oliguria in the nephrotic stage of glomerulonephritis. Immediate fatal reactions have occurred, usually as a result of ventricular failure after intravascular injection and transient high concentration of mercury in the blood. Flushing, urticaria, fever, and nausea and vomiting are common side effects. Thrombocytopenia, neutropenia, agranulocytosis, systemic mercury poisoning, and severe hypersensitivity reactions are among the more serious adverse effects of the mercurial diuretics. The drugs are contraindicated for use in the presence of renal insufficiency or acute nephritis. Because of the toxicity of these drugs, current practice usually recommends their replacement with more convenient and less toxic diuretics.