Also known as Colistimethate sodium, Colistimethate is an antibiotic that is typically injected into a muscle, or into a vein through an IV. This antibiotic basically stops the growth of bacteria, which is why it is used to treat infections caused by them. Bear in mind that if you have a kidney disease, you need to tell your doctor about it before using Colistimethate. You also need to tell them if you are pregnant or if you plan on conceiving, because it is still not known whether this medication harms an unborn baby, or if it passes into breast milk. So, to make sure that it wouldn’t harm you or your baby, seeking a professional advice is totally recommended. According to drugs.com, “Colistimethate may impair your thinking or reactions.” Therefore, you must be very careful when you drive, or when you do any other activity that requires your alertness. It is worth noting that antibiotics in general can cause diarrhea, which in turn “may be a sign of a new infection”. So, seeking medical care is what you should be doing if you have diarrhea. Besides, Colistimethate also causes severe stomach cramps, kidney problems, seizures, and fever, among others. Remember to call your doctor if you have any of these side effects. As for the common effects, they include slurred speech, dizziness, and upset stomach.