In the U.S.—

In Canada—

• Anthelmintic, systemic
• Antibacterial, systemic
• Antiprotozoal
• Bowel disease, inflammatory, suppressant

Metronidazole (me-troe-NI-da-zole) is used to treat infections. It may also be used for other problems as determined by your doctor. It will not work for colds, flu, or other virus infections.

Metronidazole is available only with your doctor's prescription, in the following dosage forms:

Oral
• Capsules (U.S. and Canada)
• Tablets (U.S. and Canada)

Parenteral
• Injection (U.S. and Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For metronidazole, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to metronidazole. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Studies have not been done in humans. Metronidazole has not been shown to cause birth defects in animal studies; however, use is not recommended during the first trimester of pregnancy.

Breast-feeding—Use is not recommended in nursing mothers since metronidazole passes into the breast milk and may cause unwanted effects in the baby. However, in some infections your doctor may want you to stop breast-feeding and take this medicine for a short time. During this time the breast milk should be squeezed out or sucked out with a breast pump and thrown away. One or two days after you finish taking this medicine, you may go back to breast-feeding.

Children—Metronidazole has been used in children and, in effective doses, has not been shown to cause different side effects or problems in children than it does in adults.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of metronidazole in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking metronidazole, it is especially important that your health care professional knows if you are taking any of the following:

• Anticoagulants (blood thinners)—Patients taking anticoagulants with metronidazole may have an increased chance of bleeding

• Disulfiram (e.g., Antabuse)—Patients taking disulfiram with metronidazole may have an increase in side effects affecting the central nervous system
• Lithium —Patients taking lithium with metronidazole may have an increased chance of experiencing lithium toxicity

• Blood disease or a history of blood disease—Metronidazole may make the condition worse

• Central nervous system (CNS) disease, including epilepsy—Metronidazole may increase the chance of seizures (convulsions) or other CNS side effects

• Heart disease—Metronidazole by injection may make heart disease worse

• Liver disease, severe—Patients with severe liver disease may have an increase in side effects
• Oral thrush or vaginal yeast infection—Metronidazole may make yeast infections worse.

If this medicine upsets your stomach, it may be taken with meals or a snack. If stomach upset (nausea, vomiting, stomach pain, or diarrhea) continues, check with your doctor. If you are taking the extended–release formulation, you should try to take it an hour before or two hours after your meal.

To help clear up your infection completely, keep taking this medicine for the full time of treatment, even if you begin to feel better after a few days. If you stop taking this medicine too soon, your symptoms may return.

In some kinds of infections, this medicine works best when there is a constant amount in the blood. To help keep the amount constant, do not miss any doses. Also, it is best to take the doses at evenly spaced times, day and night. For example, if you are to take 4 doses a day, the doses should be spaced about 6 hours apart. If this interferes with your sleep or other daily activities, or if you need help in planning the best times to take your medicine, check with your health care professional.

Dosing—

The dose of metronidazole will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of metronidazole. If your dose is different, do not change it unless your doctor tells you to do so.

The number of capsules or tablets that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking metronidazole.

• For oral dosage forms (capsules, tablets):
  • For bacterial infections:
    • Adults and teenagers—Dose is based on body weight. The usual dose is 7.5 milligrams (mg) per kilogram (kg) (3.4 mg per pound) of body weight, up to a maximum dose of 1 gram, every six hours for at least seven days.
    • Children—Dose is based on body weight. The usual dose is 7.5 mg per kg (3.4 mg per pound) of body weight every six hours; or 10 mg per kg (4.5 mg per pound) every eight hours.
  • For amebiasis infections:
    • Adults and teenagers—500 to 750 mg three times a day for five to ten days.
    • Children—Dose is based on body weight. The usual dose is 11.6 to 16.7 mg per kg (5.3 to 7.6 mg per pound) of body weight three times a day for ten days.
  • For trichomoniasis infections:
    • Adults and teenagers—A single dose of 2 grams; or 1 gram two times a day for one day; or 250 mg three times a day for seven days.
    • Children—Dose is based on body weight. The usual dose is 5 mg per kg (2.3 mg per pound) of body weight three times a day for seven days.
• For oral dosage form (extended release tablets):
  • For bacterial vaginosis:
    • Adults and teenagers—750 mg once a day for seven days.
    • Children—Use and dose must be determined by your doctor.
• For injection dosage form:
  • For bacterial infections:
    • Adults and children over 1 week of age—Dose is based on body weight. The usual dose is 15 mg per kg (6.8 mg per pound) of body weight one time to start, then 7.5 mg per kg (3.4 mg per pound) of body weight injected into a vein every six hours for at least seven days.
    • Preterm infants—Dose is based on body weight. The usual dose is 15 mg per kg (6.8 mg per pound) of body weight one time to start, then 7.5 mg per kg (3.4 mg per pound) of body weight, injected into a vein, every twelve hours starting forty-eight hours after the first dose.
    • Full-term infants—Dose is based on body weight. The usual dose is 15 mg per kg (6.8 mg per pound) of body weight one time to start, then 7.5 mg per kg (3.4 mg per pound) of body weight, injected into a vein, every twelve hours starting twenty-four hours after the first dose.
  • For treatment before and during bowel surgery:
    • Adults and teenagers—Dose is based on body weight. The usual dose is 15 mg per kg (6.8 mg per pound), injected into a vein, one hour before surgery, then 7.5 mg per kg (3.4 mg per pound) of body weight, injected into a vein, six hours and twelve hours after the first dose.
    • Children—Use and dose must be determined by your doctor.

Missed dose—

If you miss a dose of this medicine, take it as soon as possible. This will help to keep a constant amount of medicine in the blood. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store the capsule or tablet form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

If your symptoms do not improve within a few days, or if they become worse, check with your doctor.

Drinking alcoholic beverages while taking this medicine may cause stomach pain, nausea, vomiting, headache, or flushing or redness of the face. Other alcohol-containing preparations (for example, elixirs, cough syrups, tonics) may also cause problems. These problems may last for at least a day after you stop taking metronidazole. Also, this medicine may cause alcoholic beverages to taste different. Therefore, you should not drink alcoholic beverages or take other alcohol-containing preparations while you are taking this medicine and for at least 3 days after stopping it.

Metronidazole may cause dryness of the mouth, an unpleasant or sharp metallic taste, and a change in taste sensation. For temporary relief of dry mouth, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute. However, if your mouth continues to feel dry for more than 2 weeks, check with your medical doctor or dentist. Continuing dryness of the mouth may increase the chance of dental disease, including tooth decay, gum disease, and fungus infections.

This medicine may also cause some people to become dizzy or lightheaded. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert. If these reactions are especially bothersome, check with your doctor.

If you are taking this medicine for trichomoniasis (an infection of the sex organs in males and females), your doctor may want to treat your sexual partner at the same time you are being treated, even if he or she has no symptoms. Also, it may be desirable to use a condom (prophylactic) during intercourse. These measures will help keep you from getting the infection back again from your partner. If you have any questions about this, check with your doctor.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

• Less common
  • Numbness, tingling, pain, or weakness in hands or feet 
  
  

• Rare
  • Convulsions (seizures) 
  
  

Also, check with your doctor as soon as possible if any of the following side effects occur:

• Less common
  • Any vaginal irritation, discharge, or dryness not present before use of this medicine;  black, tarry stools; blood in urine or stools;  clumsiness or unsteadiness;  frequent or painful urination;  inability to control urine flow;  mood or other mental changes ;  nausea and vomiting; pinpoint red spots on skin ;  sense of pelvic pressure;  skin rash, hives, redness, or itching;  sore throat and fever;  stomach and back pain (severe);  unusual bleeding or bruising 
  
  

• For injection form
  • Pain, tenderness, redness, or swelling over vein in which the medicine is given 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Diarrhea;  dizziness or light–headedness ;  headache;  loss of appetite ;  nausea or vomiting;  stomach pain or cramps 
  
  

• Less common or rare
  • Change in taste sensation;  dryness of mouth;  unpleasant or sharp metallic taste 
  
  

In some patients metronidazole may cause dark urine. This is only temporary and will go away when you stop taking this medicine.

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although these uses are not included in product labeling, metronidazole is used in certain patients with the following medical conditions:

• Antibiotic-associated colitis
• Balantidiasis
• Dental infections
• Gastritis or ulcer due to Helicobacter pylori
• Giardiasis
• Inflammatory bowel disease

For patients taking this medicine for giardiasis:

• After treatment, it is important that your doctor check whether or not the infection in your intestinal tract has been cleared up completely.

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for this use.