Metronidazole (Apo-Metronidazole)

1. Health Canada Product Monograph — Metronidazole

• Metronidazole is used to treat bacterial vaginosis.
• Metronidazole is used to treat protozoal infections, including trichomoniasis, intestinal and liver amebiasis, and giardiasis.
• Metronidazole is used to treat serious infections caused by susceptible anaerobic bacteria, including intra-abdominal, gynecologic, skin, bone, joint, and central nervous system infections.
• Metronidazole may be used alongside another antibiotic when an infection involves both anaerobic and aerobic bacteria.

• Metronidazole should not be used during the first trimester of pregnancy.
• Metronidazole crosses the placenta; its use later in pregnancy should be carefully weighed against the potential benefit to the mother, particularly for serious infections.
• Large observational studies of women who took metronidazole during pregnancy have not shown a consistent pattern of birth defects.

• Metronidazole passes into breast milk at concentrations similar to those in the mother's blood, so it should generally be avoided while breastfeeding.
• If treatment with metronidazole is necessary, a decision should be made about temporarily interrupting breastfeeding.

• No specific dosage adjustment for metronidazole has been established for older adults based on age alone, but older patients often have reduced liver or kidney function requiring individualized dosing.

• Metronidazole has not been specifically studied for anaerobic infections or bacterial vaginosis in children, and no pediatric dosing has been authorized for these uses.
• For amebiasis and giardiasis, metronidazole has been used in children based on body-weight dosing, with close monitoring due to limited clinical experience.

• For bacterial vaginosis, the typical adult dose is 500 mg taken by mouth twice daily for 7 days.
• For trichomoniasis, treatment may be a single larger dose taken after a meal, or a 250 mg tablet taken twice daily for 10 days.
• For intestinal amebiasis, the typical adult dose is three 250 mg tablets, three times daily, for 5 to 7 days; the dose for liver amebic abscess is slightly lower.
• For giardiasis, the typical adult dose is one 250 mg tablet twice daily for 5 to 7 days.
• For anaerobic bacterial infections, treatment is usually started intravenously and then may be switched to oral metronidazole at 500 mg every 8 hours once appropriate.
• Patients with severe liver disease should receive lower doses than usual, since metronidazole and its byproducts build up more slowly in this population.
• Patients with severe kidney impairment who are not on dialysis should be monitored closely, and dose adjustment may be needed; patients on hemodialysis do not usually need a reduced dose since dialysis removes metronidazole's byproducts.
• A missed dose should be taken as soon as remembered, unless it is almost time for the next dose, in which case the missed dose should be skipped.

If overdose is suspected, seek emergency medical attention immediately or contact your regional Poison Control Centre without delay.

• Reported metronidazole overdoses of up to 12 grams as a single dose have caused vomiting, unsteady walking (ataxia), and mild disorientation.
• Nerve-related effects, including seizures and peripheral neuropathy, have been reported after several days of very high oral doses.
• There is no specific antidote for metronidazole overdose.
• Early gastric lavage may help remove the drug if performed soon after ingestion; otherwise, treatment is supportive and based on symptoms.

• Nausea may occur.
• An unpleasant metallic taste in the mouth may occur.
• Loss of appetite may occur.
• Diarrhea may occur.
• Stomach pain or cramping may occur.
• Headache may occur.
• Dizziness may occur.
• Dry mouth may occur.
• A furred or discoloured tongue may occur.
• Darkened urine may occur; this is harmless and related to a drug breakdown product.

Serious side effects require immediate discussion with the prescriber or emergency care.

• Severe skin reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS syndrome, have been reported and require immediate medical attention.
• Seizures and peripheral nerve damage, such as numbness, tingling, or weakness in the hands or feet, have occurred, particularly with high doses or prolonged use.
• A rare but serious brain-related reaction (encephalopathy), with symptoms such as unsteady walking, confusion, and slurred speech, has been reported.
• Aseptic meningitis, with symptoms such as headache, fever, stiff neck, and sensitivity to light, has been reported.
• Severe liver injury, including liver failure requiring transplant, has been reported rarely, especially when metronidazole is combined with other antibiotics.
• Severe, sometimes fatal liver failure has occurred specifically in patients with Cockayne syndrome, which is why this drug must never be used in that population.
• Blood cell abnormalities, including a drop in white blood cells or platelets, may occur.
• Suicidal thoughts, with or without depression, have been reported during treatment.
• A fast or irregular heartbeat, including QT interval prolongation, has been reported, particularly when combined with other drugs that affect heart rhythm.
• A rare but serious allergic reaction (anaphylaxis) or swelling of the face and throat (angioedema) may occur.
• Seek urgent medical attention for a severe skin rash, difficulty breathing, seizures, or confusion or unsteady walking that develops during treatment.

• Use with caution in patients with active nervous system disease or a history of seizures, due to the risk of neurological side effects.
• Use with caution in patients with severe liver disease, since the drug clears from the body more slowly and may accumulate.
• Use with caution in patients with severe kidney impairment, particularly those not undergoing dialysis.
• Use with caution in patients with a blood disorder or history of low blood cell counts, since periodic blood tests are recommended during prolonged or repeated treatment.
• Use with caution in patients who need to drive or operate machinery, since confusion, dizziness, and vision changes can occur.
• Use with caution in patients who may be at risk of inflammatory bowel disease, since metronidazole use has been linked to an increased risk.
• Patients taking metronidazole for the first time should not be left unattended for two hours after the first dose, due to rare reports of sudden, serious nerve-related reactions.

• Contraindicated in patients with known hypersensitivity to metronidazole, other nitroimidazole drugs, or any ingredient in the formulation.
• Contraindicated in patients with Cockayne syndrome, due to the risk of severe, sometimes fatal, liver failure.
• Contraindicated in patients with active neurological disorders or a history of a blood cell disorder (blood dyscrasia).
• Contraindicated in patients with hypothyroidism or hypoadrenalism (an underactive thyroid or adrenal gland).

• Alcohol must be avoided during metronidazole treatment and for at least one day afterward, since combining them can cause flushing, vomiting, and a fast heartbeat.
• Disulfiram must not be used together with metronidazole, as the combination has been linked to confusion and psychotic reactions.
• Warfarin and other blood thinners may have a stronger effect when combined with metronidazole, increasing bleeding risk; clotting tests should be monitored more often.
• Lithium levels may rise when combined with metronidazole, increasing the risk of lithium toxicity.
• Phenytoin and phenobarbital may affect how quickly metronidazole is cleared from the body, and phenytoin levels themselves may become elevated during combined use.
• Busulfan levels may rise significantly when combined with metronidazole, increasing the risk of busulfan toxicity.
• Cyclosporine levels may rise when combined with metronidazole, requiring monitoring of both cyclosporine and kidney function.
• Other drugs that affect heart rhythm (QT-prolonging drugs) may increase the risk of an abnormal heart rhythm when combined with metronidazole.
• 5-fluorouracil clearance may be reduced by metronidazole, increasing the risk of 5-fluorouracil toxicity.
• Cimetidine and other drugs that slow liver enzyme activity may raise metronidazole blood levels.

• Metronidazole can be taken with or without food; taking it with food may help reduce nausea or stomach upset for patients who are sensitive to it.

• Metronidazole is usually taken at evenly spaced times through the day, for example every 8 to 12 hours, to keep a steady level of the drug in the body; it can be taken with or without food.
• The full course of treatment should be completed even if symptoms improve early, to fully clear the infection.

• Store metronidazole tablets at room temperature, between 15°C and 30°C, and protect from light.

• Metronidazole is an antibiotic used to treat certain bacterial and parasitic infections, including bacterial vaginosis, trichomoniasis, amebiasis, and giardiasis.
• Complete the full course of treatment, even if you start feeling better, to make sure the infection is fully treated.
• Avoid alcohol during treatment and for at least one day after finishing, since it can cause an unpleasant reaction.
• Contact your doctor right away if you develop numbness or tingling, unsteady walking, a severe skin rash, or new mood changes.
• Metronidazole may darken your urine; this is a harmless effect of the drug and not a cause for concern.