It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it.
If severe or persistent (non-stop) diarrhea occurs while using methylnaltrexone injection, stop using this medicine and check with your doctor right away.
Stop using this medicine and check with your doctor right away if you have severe abdominal or stomach pain or cramps; bloody, black, or tarry stools; heartburn; indigestion; nausea; or vomiting of material that looks like coffee grounds. These could be symptoms of a serious bowel problem called intestinal perforation.