title: Letter: Concentration of morphine equivalent in urine.
mesh_terms: D006801:Humans; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D008702:Methaqualone / Q000097:blood / Q000652:urine*; D009020:Morphine / Q000652:urine*
chemical_list: D009020:Morphine; D008702:Methaqualone