Pharmacology. Unithiol (DMPS; 2,3-dimercaptopropanol-sulfonic acid), a dimercapto chelating agent that is a water-soluble analog of BAL (See BAL (Dimercaprol)), is used in the treatment of poisoning by several heavy metals, principally mercury, arsenic, and lead. Available on the official formularies of Russia and former Soviet countries since 1958 and in Germany since 1976, unithiol has been legally available from compounding pharmacists in the United States since 1999. The drug can be administered orally and parenterally. Oral bioavailability is approximately 50%, with peak blood concentrations occurring in approximately 3.7 hours. It is bound extensively to plasma proteins, mainly albumin. More than 80% of an intravenous dose is excreted in the urine, 10% as unaltered unithiol and 90% as transformed products, predominantly cyclic DMPS sulfides. The elimination half-life for total unithiol is approximately 20 hours. Unithiol and/or its in vivo biotransformation products form complexes with a variety of inorganic and organic metal compounds, increasing excretion of the metal in the urine and decreasing its concentration in various organs, particularly the kidneys. Renal elimination of the metal chelates appears to be mediated in part by the multidrug resistance protein 2 (Mrp2). Unlike BAL, unithiol does not redistribute mercury to the brain.