Depending on their physiochemical properties, foreign substances appear to a more or less substantial degree in mother's milk. The decision as to whether a drug may be administered during nursing is particularly difficult in the case of antibiotics. Due to the development of resistance and sensitization only a few of these drugs are allowed. A nursing stop should only be ordered when a dangerous drug is used with genuine indication and without a possible alternative. As a rule, those drugs which are believed to involve a certain danger for newborn, can be replaced by other nonhazardous drugs.