The reason sulfa drugs are avoided in the newborn period is because the drug
displaces bilirubin and theoretically could contribute to kernicterus(the
condition that involves brain damage and is the reason behind the fear of
jaundice in babies) It is really only a theoretical concern unless the baby is
very jaundiced (bili in the high teens) or the baby is very sick. Otherwise I
would just monitor the baby closely for signs of increasing bili.

Mary Murphy, M.D.