Bilirubin dimethyl ester is a natural derivative of bilirubin and is found in normal sera representing an average of 1.75% total sera bilirubin. Bilirubin is a water insoluble tetrapyrrole produced from the reduction of biliverdin in a reaction catalyzed by the enzyme bilirverdin reductase. Water insoluble bilirubin (also called indirect bilirubin) in vivo undergoes glucuronidation in the liver (addition of one or two glucuronic acids through a glycosidic bond) to form the water soluble bilirubin mono or diglucuronide (also called bilirubin conjugate or direct bilirubin). Bilirubin conjugate is excreted from the liver in bile or is converted to urobilinogen and excreted in the urine as urobilin or in the feces as stercobilin. Bilirubin dimethyl ester has been found to be converted to bilirubin conjugate via esterase and glucuronidase activity in vivo.
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