Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).
Call your doctor at once if you have:
severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);
thrush (white patches inside your mouth or throat);
heart problems--fast heartbeats, chest pain or pressure, pain spreading to your jaw or shoulder, nausea, sweating;
liver problems--nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); or
signs of a new infection--fever, headache, tiredness, ear pain or drainage, eye pain or redness, cough, skin rash, sores or pimples with pus, joint pain, ongoing neck or back pain, diarrhea, pain or burning when you urinate.
Common side effects may include:
diarrhea;
rash;
swollen, black, or "hairy" tongue;
vaginal itching or discharge;
pain where the medicine was injected.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Unasyn side effects (more detail)
