Stomach upset, diarrhea/loose stools, nausea, vomiting, or abdominal pain may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor right away if any of these unlikely but serious side effects occur: hearing changes (such as decreased hearing, deafness), eye problems (such as drooping eyelids, blurred vision), difficulty speaking/swallowing, muscle weakness, signs of liver problems (such as unusual tiredness, persistent nausea/vomiting, severe stomach/abdominal pain, yellowing eyes/skin, dark urine). Get medical help right away if any of these rare but serious side effects occur: fast/irregular heartbeat, severe dizziness, fainting. This medication may rarely cause a severe intestinal condition (Clostridium difficile-associated diarrhea) due to a resistant bacteria. This condition may occur during treatment or weeks to months after treatment has stopped. Do not use anti-diarrhea or opioid medications if you have any of the following symptoms because these products may make them worse. Tell your doctor right away if you develop: persistent diarrhea, abdominal or stomach pain/cramping, blood/mucus in your stool. Use of this medication for prolonged or repeated periods may result in oral thrush or a new yeast infection. Contact your doctor if you notice white patches in your mouth, a change in vaginal discharge, or other new symptoms. A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: fever that doesn't go away, new or worsening lymph node swelling, rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. An allergic reaction to this medication may return even if you stop the drug. If you have an allergic reaction, continue to watch for any of the above symptoms for several days after your last dose. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.