Indomethacin therapy of patent ductus in preterm infants controlled by plasma levels.

Indomethacin was given by suppository to 18 neonates for the treatment of patent ductus arteriosus. The plasma levels of the drug were measured by high pressure liquid chromatography. Permanent closure of the ductus was achieved in 12 of 21 treatments and took up to 48 h. Successful treatment was strongly associated with a plasma indomethacin level greater than 0.5 micrograms/ml in the 8 h after a dose. Decreased urinary output was more likely at the same level, but was also found with substantially lower figures. It is suggested that indomethacin therapy for patent ductus should be rationalized by measurement of the plasma level.