Surprising results from a drug administered to premature infants

I was recently thinking about the increasing number of articles that I read where one drug, used to treat one disease, is later found to be useful in treating a second, different disease. Are the biochemical pathways so similar that the two different diseases can be treated by the same drug? Was the biochemistry of the second disease just previously not well understood, and now that scientists understand the underlying pathways of the second disease, they have realized the drug might be used to treat it? Or was it a coincidence that a patient that had both diseases was cured of the second disease by treating the first disease with the drug? Do the drugs affect multiple biochemical pathways, and did we just not know about the other pathways that were affected? What happens to the other biochemical pathways that are affected if you only have the first disease - is this what causes "side-effects"? And, finally, shouldn't we be concerned??

Today, I read a headline that is a bit different, and also disconcerting. The headline reads "Drug Therapy for Premature Infants Destroys Brain Cells in Mice". You may see the synopsis here. The class of drugs studied are lifesaving in their use to develop lungs in premature infants. By correlating this class of drugs to the adverse effect of killing neural progenitor cells, the scientists realized that these drugs may cause brain damage. The good news: With this finding, doctors can use greater caution weighing the benefits versus risks when treating premature patients, while the scientists can strive to develop better, more targeted drugs.