Metronidazole is an antibiotic that is used to treat bacterial infections of the vagina, stomach, liver, skin, joints, brain and spinal cord, lungs, heart, or bloodstream.

Metronidazole is also used to treat trichomoniasis, a sexually transmitted disease caused by a parasite. Usually both sexual partners are treated at the same time, even if one has no symptoms.

Do not use metronidazole to treat any condition that has not been checked by your doctor.

Metronidazole may also be used for purposes not listed in this medication guide.

You should not use this medicine if you are allergic to metronidazole, secnidazole, or tinidazole, or if:

• you drank alcohol in the past 3 days;
• you consumed foods or medicines that contain propylene glycol in the past 3 days; or
• you took disulfiram (Antabuse) within the past 14 days.

May harm an unborn baby. Do not use metronidazole to treat trichomoniasis during the first trimester of pregnancy. Tell your doctor if you become pregnant.

Not all uses of metronidazole are approved for treating children and teenagers. Metronidazole is not approved to treat vaginal infections in girls who have not begun having menstrual periods.

Tell your doctor if you have ever had:

• liver disease;
• kidney disease (or if you are on dialysis);
• a heart rhythm disorder;
• a stomach or intestinal disease such as Crohn's disease;
• a blood cell disorder such as anemia (lack of red blood cells) or low white blood cell (WBC) counts;
• a fungal infection anywhere in your body; or
• a nerve disorder.

Metronidazole has caused cancer in animal studies. However, it is not known whether this would occur in humans. Ask your doctor about your risk.

You should not breastfeed within 24 hours after using metronidazole. If you use a breast pump during this time, throw out the milk and do not feed it to your baby.

Use Protostat (Oral) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Get emergency medical help if you have signs of an allergic reaction (hives, itching, warmth or tingling; fever, joint pain; dry mouth, dry vagina; stuffy nose, 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:

• new or worsening symptoms of infection;
• painful or difficult urination;
• confusion;
• a light-headed feeling (like you might pass out);
• vaginal itching or discharge; or
• blisters or ulcers in your mouth, red or swollen gums, trouble swallowing.

Stop taking the medicine and call your doctor right away if you have neurologic side effects (more likely to occur while taking metronidazole long term):

• numbness, tingling, or burning pain in your hands or feet;
• vision problems, pain behind your eyes, seeing flashes of light;
• muscle weakness, problems with speech or coordination;
• trouble speaking or understanding what is said to you;
• a seizure; or
• fever, neck stiffness, and increased sensitivity to light.

Metronidazole can cause life-threatening liver problems in people with Cockayne syndrome. If you have this condition, stop taking metronidazole and contact your doctor if you have signs of liver failure--nausea, stomach pain (upper right side), dark urine, clay-colored stools, or jaundice (yellowing of the skin or eyes).

Side effects may be more likely in older adults.

Common side effects may include:

• depression, trouble sleeping, feeling irritable;
• headache, dizziness, weakness;
• nausea, vomiting, loss of appetite, stomach pain;
• diarrhea, constipation;
• unpleasant metallic taste;
• rash, itching;
• vaginal itching or discharge, pain during sex;
• mouth sores; or
• swollen, red, or "hairy" 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.

While taking metronidazole and for 3 days after your last dose: Do not drink alcohol or consume foods, medicines, or other products that contain alcohol or propylene glycol. You may have unpleasant effects such as headaches, nausea, vomiting, stomach cramps, and warmth or tingling under your skin.