Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
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);
pale, gray, or bluish skin;
fever, weakness;
sore or swollen tongue;
easy bruising, purple or red spots under your skin;
a skin rash, no matter how mild; or
high potassium level--nausea, weakness, tingly feeling, chest pain, irregular heartbeats, loss of movement.
Common side effects may include:
vomiting, diarrhea, stomach pain;
rash, itching; or
swelling in your tongue.
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.
 Trimethoprim side effects (more detail)
