ELIZA CINTEZA, ANDA UNGUREANU, MIHAELA BALGRADEAN, ALIN NICOLESCU BENEFICIAL EFFECTS OF ACETAMINOPHEN ON THE CHEMICAL MEDIATORS INVOLVED IN THE CLOSURE OF PATENT DUCTUS ARTERIOSUS Paracetamol (N-acetyl- para-aminophenol) also known as acetaminophen is a chemical compound used in medical practice for analgesic and antipyretic effects. The mechanism of action is related to the cyclooxygenase (COX) activity, which is not full inhibit as for nonsteroidal anti-inflammatory. Paracetamol selectively inhibits COX activities in the brain, indirectly by reducing COX, which must be oxidized in order to function. In addition to analgesic and antipyretic effects, modulating the prostaglandin synthesis by selective inhibition of COX, a vascular modulator effect was described recently on the closure of the patent ductus arteriosus (PDA). This effect has been described in premature newborns, perhaps by decreasing the prostaglandin production. We present the case of a neonate, 39 weeks gestational age, normal birth weight who presented in the 10 th day of life with a cardiac murmur. Echocardiography evidenced a hemodynamically significant PDA, left ventricular enlargement, severe mitral regurgitation, patent foramen ovale and pulmonary hypertension. Although she was a 10-day- old full-term neonate paracetamol administration was attempted. Paracetamol was administered orally in the therapeutic dose of 15 mg/kg/dose, three times a day for three days. The effect was significant by reducing the diameter of the arterial duct (~50% of initial diameter), reducing the size of the left cardiac chambers, reducing the degree of mitral regurgitation from severe to mild, and disappearance of pulmonary hypertension. In conclusion, paracetamol use can change prognosis through the vaso-modulator on the PDA, at the age of 10 days, on a full-term neonate with a normal birth weight. This effect may also be present in full-term newborns and not only in preterm. Even if the PDA was not closed after three days, the hemodynamic impact disappeared and the child could avoid surgical ligation.