paramagnetic chelates , as for example , gadolinium diethylenetriaminepentaacetic acid , manganese , ethylenediaminetetraacetic acid , and others used as x - ray contrast agents are more toxic acutely when injected in high concentration or at rapid rates . the use of effective amounts of calcium in the form of , calcium chloride , calcium gluconate , or balanced salt solutions substantially reduces this toxicity without the need to add additional ligand .