Consequences associated with nonnarcotic analgesics in the fetus and newborn

Nonnarcotic analgesics include well-known, widely used substances such as acetylsalicylic acid (ASA) and acetaminophen. ASA is a potent inhibitor of prostaglandin synthesis, and this mechanism is responsible for many potential toxicities in the fetus and newborn. These may include bleeding, altered renal function, and constriction of the ductus arteriosus in addition to analgesia. As such, ASA is frequently avoided during gestation and the immediate neonatal period. Acetaminophen is less well recognized as an agent with activity outside the central nervous system. It does not possess antiinflammatory activity like other substances that inhibit prostaglandins but has been shown to be an analgesic with potency comparable to ASA. This is believed to be by inhibition of brain prostaglandin synthetase. We have determined by using the chronically catheterized sheep fetus that acetaminophen has potent activity on the ductus arteriosus and produces a constriction, in therapeutic analgesic quantities, comparable to ASA. Thus, acetaminophen may be a potent inhibitor of prostaglandin function in the fetus.