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Generic Name

Metronidazole(me troh NI da zohl)


Trade Name

Flagyl (250 mg, 375 mg, 500 mg, 750 mg ER )
Protostat (250 mg, 500 mg )
This drug is available in a generic form.


What is Metronidazole?

This drug is an antibiotic which kills bacteria and clears up infection within the body.


What is it used for?

Metronidazole is used for many different bacterial infections. When used with other antibiotics it can cure the stomach infection called Helicobactor pylori gastritis. It is also a useful drug in treating the infection that often is present in Crohn’s disease.


How do I take it?

Follow your physician’s instructions carefully. Metronidazole may be taken with or without food. It may also be taken with milk to avoid stomach upset. Tablets may be crushed and the capsules may be opened and sprinkled on soft food. Try to take doses at approximately the same time each day. Store at room temperature in a tightly sealed container. Keep all medications away from children. Never share your medications with anyone else.


What do I do for a missed dose?

As with all antibiotics, metronidazole works best when there is a constant, steady blood level. Therefore, the doses should be evenly spaced and not missed. If you do miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the one you missed and go back to your regular schedule. Do not take 2 doses at once.


Are there interactions with food or beverages?

There are no known interactions with foods. Alcohol should be avoided during and for 3 days after taking Metronidazole. The combination of Metronidazole with alcohol can cause severe abdominal cramps, nausea, vomiting and headaches. Be aware of “hidden” alcohol in over-the-counter preparations such as cough and cold remedies and mouthwashes. Read labels or ask your physician.


Are there interactions with other drugs?

An interaction generally means that one drug may increase or decrease the effect of another drug. Also, the more medications a person takes, the more likely there will be a drug interaction.

Interactions with this drug may occur with the following:

  • blood thinners (Coumadin)
  • cholestyramine (Questran)
  • disulfiram (Antabuse)
  • cimetidine (Tagamet)
  • phenytoin (Dilantin)
  • phenobarbital
  • lithium (Eskalith)
  • antacids
  • birth control pills


Is there a problem if I have another disorder or disease?

At times, a drug may have a different or enhanced effect when other diseases are present. At other times, the drug may worsen or effect another disease. Metronidazole is metabolized by the liver so patients with severe liver disease such as cirrhosis should be cautious and discuss it with the physician.


What about allergies?

People who have known allergies or asthma may be at an increased risk for a reaction from any new medication. The physician should always know a patient’s allergy history. Signs of an allergic reaction are skin rash, hives and itching. Of course, a person should not take metronidazole if there has been a previous reaction to this or a similar drug.


What if I’m pregnant, considering pregnancy or breast-feeding?

Most females now know that, if possible, no drug, including alcohol, should be taken during pregnancy or lactation. The potential danger, of course, is an injury to the baby. However, some drugs are much safer than others in this regard. So, the FDA has a grading system for each drug which reflects what is known medically. It ranks drugs from A, where medical studies show no evidence for danger to the fetus or mother, to B, C, D and X, where the medical evidence indicates that the risk to the fetus outweighs any benefit to the mother. Metronidazole is ranked B. Always consult your physician before taking any drug during or when planning pregnancy.


What are the effects on sexual function?

Metronidazole can cause a decreased sexual drive and decreased vaginal secretions that can result in painful or difficult intercourse.


Are there other precautions?

  • Troublesome and persistent diarrhea can develop. If diarrhea persists for more than 24 hours, discontinue the medication and contact your physician.
  • Sensitive individuals or those exposed to prolonged or repeated antibiotic use may develop other infections due to yeast organisms. These will usually occur in the mouth, genital or anal regions.
  • Metronidazole may cause drowsiness or lightheadedness. Restrict driving and other activities as necessary.
  • It may cause dark discoloration of urine which has no significance.


How long is it safe to take Metronidazole?

Metronidazole is often used for prolonged periods of time, especially in treating Crohn’s disease. It appears to be quite safe in this regard.


How about side effects?

Adverse reactions can occur with any drug, even over-the-counter medications. Some of these are mild such as a stomach upset, which may be avoided by taking the medication with food. Minor reactions may go away on their own but if they persist, contact the physician. For major reactions, the patient should contact the physician immediately.

For Metronidazole, the following are the observed side effects:


  • unpleasant metallic taste
  • headache
  • dizziness
  • fatigue
  • dry mouth
  • stomach cramps
  • nausea
  • vomiting
  • diarrhea
  • dark urine (no significance)
  • rash
  • hives
  • itching


  • changes in mood or mental function
  • unsteadiness
  • numbness, pain or weakness in hands or feet
  • seizures
  • fever
  • sore throat


A physician’s comment…

Most antibiotics taken by mouth are fairly safe. However, resistance to these drugs does occur when they are used too often. Therefore, they should only be used for specific purposes and for the length of time decided by the physician.