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The side effects listed above may not include all of the side effects reported by the drug's manufacturer.
How can this medicine affect other medicines?
It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while using this one, to ensure that the combination is safe.
You should avoid alcohol while using this antibiotic, and for at least 48 hours after finishing the course, as this can cause unpleasant symptoms such as hot flushes, abdominal cramps, nausea, vomiting, headache and palpitations.
Metronidazole may enhance the anti-blood-clotting effect of anticoagulant medicines such as warfarin and nicoumalone, and this may increase the risk of bleeding. If you are taking an anticoagulant medicine your blood clotting time (INR) should be monitored during treatment with a course of metronidazole, and your doctor may need to reduce your anticoagulant dose.
Metronidazole may increase the blood levels of the following medicines:
Barbiturates, such as the antiepileptic medicine phenobarbital, decrease the blood level of metronidazole and may make it less effective at treating infection. Your doctor may prescribe you a larger than normal dose of metronidazole if you are taking a barbiturate.
If metronidazole is taken by people taking disulfiram there may be a risk of confusion and psychotic symptoms such as paranoia and hallucinations. This combination should be avoided where possible or closely monitored if essential.
If you are taking a combined oral contraceptive pill or are using contraceptive patches, there may be a very low risk that this antibiotic may make it less effective at preventing pregnancy. Although the risk of this is very low, the personal and ethical consequences of an unwanted pregnancy can be very serious. For this reason, the Family Planning Association recommends that women using a combined contraceptive pill or patch should use an extra method of contraception (eg condoms) while taking a short course of broad-spectrum antibiotic, and for seven days after finishing the antibiotic course. If these seven days run beyond the end of a pill packet, a new packet should be started without a break (in the case of ED pills the inactive tablets should be omitted). If the seven days run beyond the 3 weeks of a patch cycle, a new cycle should be started immediately without a patch-free break.
Other medicines containing the same active ingredient
Oral and rectal brands of metronidazole:
| Flagyl S | Flagyl tablets | Metrolyl suppositories |
| Norzol |
Brands of metronidazole that are applied to the skin:
| Anabact | Metrogel | Metrosa |
| Metrotop | Rozex | Zyomet |
| Zidoval |