BMA Concise Guide to Medicine & Drugs


Brand names Anabact, Elyzol, Flagyl, Metrogel, Metrolyl, Metrotop, Rosiced, Rozex, Vaginyl, Zidoval, Zyomet

Used in the following combined preparations None


Drug group Antibacterial drug and antiprotozoal drug

Overdose danger rating Low

Dependence rating Low

Prescription needed Yes

Available as generic Yes


Metronidazole is prescribed to treat both protozoal infections and a variety of bacterial infections.

It is widely used in the treatment of trichomonas infection of the vagina. Because the organism responsible for this disorder is sexually transmitted and may not cause any symptoms, a simultaneous course of treatment is usually advised for the sexual partner.

Certain infections of the abdomen, pelvis, and gums also respond well to metronidazole. The drug is used to treat septicaemia and infected leg ulcers and pressure sores. It is also used to treat Clostridium difficile infections associated with antibiotic use. Metronidazole may be given to prevent or treat infections after surgery. Because the drug in high doses can penetrate the brain, it is prescribed to treat abscesses occurring there.

Metronidazole is also prescribed for amoebic dysentery and giardiasis, a protozoal infection.


Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets, liquid, injection, suppositories, gel, cream.

Frequency and timing of doses 3 x daily for 5–10 days, depending on condition being treated. Sometimes a single large dose is prescribed. Tablets should be taken after meals and swallowed whole with plenty of water. 1–2 x daily (topical preparations).

Adult dosage range 600–2,000mg daily (by mouth); 3g daily (suppositories); 1.5g daily (injection).

Onset of effect The drug starts to work within an hour or so, but beneficial effects may not be felt for 1–2 days.

Duration of action 6–12 hours.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children. Protect from light.

Missed dose Take as soon as you remember. If your next dose is due within 2 hours, take a single dose now and skip the next.

Stopping the drug Take the full course. Even if you feel better the infection may still be present and symptoms may recur if treatment is stopped too soon.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. But if you notice unusual symptoms, especially numbness or tingling, or if a large overdose has been taken, notify your doctor.


Various minor gastrointestinal symptoms (such as nausea and loss of appetite) are common but tend to diminish with time. Metronidazole also often causes darkening of the urine, but this is no cause for concern. More rarely, the drug may cause dry mouth, a metallic taste, headache, or dizziness. More serious adverse effects on the nervous system, causing numbness or tingling, are extremely rare but should be reported to your doctor.


Oral anticoagulants, ciclosporin, phenytoin, and fluorouracil Metronidazole may increase the effects of these drugs.

Lithium Metronidazole increases the risk of adverse effects on the kidneys.

Cimetidine This drug may increase the levels of metronidazole in the body.

Phenobarbital This drug may reduce the effects of metronidazole.


Be sure to tell your doctor if:

· You have long-term liver or kidney problems.

· You have porphyria.

· You are taking other medicines.

Pregnancy Safety in pregnancy not established. Discuss with your doctor.

Breast-feeding The drug passes into the breast milk, but at normal doses adverse effects on the baby are unlikely. However, metronidazole may give the milk a bitter taste. Discuss with your doctor.

Infants and children Reduced dose necessary.

Over 60 No special problems.

Driving and hazardous work Avoid such activities until you have learned how metronidazole affects you because the drug can cause drowsiness.

Alcohol Avoid. Taken with metronidazole, alcohol may cause flushing, nausea, vomiting, abdominal pain, and headache.


Not usually prescribed for longer than 10 days. Prolonged treatment may cause loss of sensation in the hands and feet (usually temporary), and may also reduce production of white blood cells.