How long does metronidazole stay in your system?
The time the organism needs to eliminate half of metronidazole varies strongly. It can take from 5 to 42 hours before half of this antibiotic is excreted from the organism [1].
Multiple factors determine how long metronidazole will stay in your system.
The metabolism of metronidazole depends on liver function. When the liver is healthy, it typically takes around 8 hours to metabolize half of the antibiotic [2].
However, when the liver suffers from a disease, the elimination time of metronidazole can increase. For example, patients with obstructive liver disease will need up to 42 hours to clear half of metronidazole [1].
Other factors that influence how long metronidazole stays in your system. They include the frequency of administration, the dose of the antibiotic, and your metabolic rate.
Which infections are treated with metronidazole?
Metronidazole is a versatile antibiotic that can be used to treat a variety of infections. This antibiotic can be prescribed for bacterial and parasitic infections.
Metronidazole can be used for:
- trichomonas infections [3],
- giardiasis [3],
- entamoeba histolytica infections [3],
- giardia lamblia infections [3],
- bacterial vaginosis [4],
- nonspecific vaginitis (a mixed infection by anaerobes and Gardnerella vaginalis [5],
- bacteroides species infections (like Bacteroides fragilis) [6],
- Fusobacteria infections [6],
- Clostridia infections [6].
What are the risks of metronidazole?
Metronidazole, like most drugs, has been associated with several side effects.
The most common side effects of metronidazole are:
- nausea,
- abdominal pain,
- diarrhea [7].
Another significant risk associated with metronidazole is its potential carcinogenic effect. Especially at risk of malignancy development are patients who take high doses for a long time [11].
Also, in rare cases, metronidazole can lead to the development of aplastic anemia [12].
If you are pregnant, you should not take metronidazole. Metronidazole can interfere with embryonic implantation and development. It also increases the probability of placental pathologies occurrence.
Metronidazole can be neurotoxic.
Metronidazole can cause cerebellar dysfunction. Its use can lead to changes in brain structure (like changes in the red nucleus and dentate). In rare cases, the administration can lead to optic neuropathy, peripheral neuropathy, and encephalopathy. You should visit a doctor when experiencing symptoms like problems with coordination, problems with sight, vertigo, or headaches.
How long should you take metronidazole?
Typically, metronidazole is prescribed for 10–15 days [14].
The dosing varies. It can be taken once, up to four times daily [15].
In bacterial infections, the twice-a-day dose is shown to be as effective as the four-times-a-day dose [2].
Prolonged use of metronidazole increases the chance of side effects. Four-month therapy can lead to the development of peripheral neuropathy, convulsions, and cerebellar ataxia [14].
Therefore, you should never prolong the metronidazole therapy on your own. Longer treatments should always be under a doctor’s supervision.
What drugs interact with metronidazole?
Among the most dangerous interactions of metronidazole are:
- warfarin,
- amiodarone,
- carbamazepine,
- quinidine,
- tacrolimus,
- cyclosporine.
Metronidazole’s interaction with warfarin is dangerous. It leads to an increase in anticoagulation and increases the risk of bleeding [16, 17, 18]. Therefore, you always have to tell your doctor the full list of medications you are taking.
Interaction with amiodarone, carbamazepine, quinidine, tacrolimus, and cyclosporine leads to an increased concentration of these drugs in the blood. Long-term exposure to high amounts of these drugs can lead to toxic effects [19].
Lastly, metronidazole can interact with alcohol-containing medications. This can lead to a disulfiram-like reaction [20].