Gadolinium is a rare earth element.
The free gadolinium ion is unsuitable for clinical use due to high toxicity, however, the metal chelate is metabolically inert. The organic component of the chelate is not measurably metabolized and the metal does not dissociate. After i.v. injection of gadopentetate dimeglumine, the meglumine ion completely dissociates from the gadopentetate. The hydrophylic chelate is distributed only in the extracellular water and does not cross the intact blood-brain barrier. Gadopentetate is excreted unchanged in the urine.