(11β,?17α)?-17-?[(Ethoxycarbonyl)?oxy]?-?11-?hydroxy-?3-?oxo-?androsta-?1,?4-?diene-?17-?carboxylic acid-d5 is labelled (11β,?17α)?-17-?[(Ethoxycarbonyl)?oxy]?-?11-?hydroxy-?3-?oxo-?androsta-?1,?4-?diene-?17-?carboxylic acid (E890570) which is a derivative of Loteprednol Etabonate (L471400) which is an ophthalmic corticosteroid.