The side effects associated with the use of generic Septra medication could include an outbreak of hives due to an allergic reaction, loss or change in appetite, nausea, rash of the skin or vomiting. If other medication is being taken it is important that a local physician is aware of those other medications to ensure there are no negative interactions. A partial list of medications to be aware of for interactions include blood thinners, Digoxin, Cyclosporine, Indomethacin, Methotrexate, Pyrimethamine and Amantadine. If extreme diarrhea occurs after you buy Septra, it is important to contact a local physician immediately.