Home » Antibiotics » Flagyl
Brand Names: Flagyl, Metrogyl, Trichozole
Generic Name: Metronidazole
Generic name: Metronidazole
Brand names: Flagyl, Metrogyl, Trichozole
How does Flagyl work?
Flagyl tablets contain the active ingredient metronidazole, which is a type of medicine called an antibiotic. (NB. Metronidazole is also available without a brand name, ie as the generic medicine.) Metronidazole is used to treat infections caused by bacteria and other micro-organisms called protozoa.
Metronidazole works by entering bacterial and protozoal cells and interfering with their genetic material (DNA). It damages the DNA and also prevents the bacteria and protozoa from forming new DNA. This ultimately results in metronidazole killing the micro-organisms, which clears up the infection.
Metronidazole kills a wide variety of bacteria that are known collectively as anaerobic bacteria. This means that they do not need oxygen to grow and multiply. Anaerobic bacteria can cause infections in areas of the body such as the bones, gut, pelvic cavity and gums. Metronidazole is used to treat these types of infections, as well as leg ulcers and pressure sores that are infected with anaerobic bacteria.
Metronidazole is also used to prevent infection following surgery, particularly gynaecological surgery and surgery on the gut, where many anaerobic bacteria may be found. In high doses, metronidazole penetrates the brain and can be used to treat abscesses in the brain.
Metronidazole is also used to treat infections with protozoa. These micro-organisms are also anaerobic and include Trichomonas vaginalis (which causes trichomonas infection of the vagina) and other protozoa, such as Entamoeba histolytica (which causes amoebic dysentry) and Gardia lambila (which causes giardiasis).
To make sure the micro-organisms causing an infection are susceptible to metronidazole your doctor may take a tissue sample, for example a swab from the infected area.
Flagyl tablets are taken by mouth, but metronidazole may also be given by suppository, or via a drip into a vein (intravenous infusion) for more serious infections or when administration by mouth is not possible.
What is Flagyl used for?
• Preventing and treating infections with anaerobic bacteria following surgery, particularly surgery on the gut or gynaecological surgery
• Bacterial infection of the blood (septicaemia or blood poisoning)
• Bacterial infection of the blood following childbirth (puerperal fever/sepsis)
• A serious form of pneumonia (necrotising pneumonia)
• Bacterial infections of bone (osteomyelitis)
• Bacterial infections in the abdomen (peritonitis)
• Abscess in the pelvic cavity, usually a result of an abdominal infection
• Inflammation of the connective tissue and muscle around the uterus due to bacterial infection (pelvic cellulitis)
• Brain abscesses
• Bacterial dental infections, eg dental abscesses
• Painful inflammation and ulcers of the gums (ulcerative gingivitis)
• Bacteria infected leg ulcers
• Bacteria infected pressure sores
• Bacterial infection of the vagina (bacterial vaginosis)
• Protozoal infection of the urinary organs or genitals (urogenital trichomoniasis)
• Protozoal infection of the intestine (amoebiasis or amoebic dysentry)
• Parasitic gut infection caused by the protozoa Giardia lamblia (giardiasis)
• Metronidazole tablets should be taken with plenty of water with or after food. The tablets should be swallowed whole and not chewed.
• You should not drink alcohol while taking 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.
• This medicine may cause various side effects that could impair your mental or physical ability to safely drive or operate machinary. You should be aware of how you react to this medicine before driving or operating machinary.
• Unless your doctor tells you otherwise, it is important that you finish the prescribed course of this antibiotic medicine, even if you feel better or it seems the infection has cleared up. Stopping the course early increases the chance that the infection will come back and that the bacteria will grow resistant to the antibiotic.
• If your treatment course exceeds 10 days it is recommended that you are monitored by your doctor, who may carry out tests to check for side effects and that the medicine is working properly.
Use with caution in
• Decreased liver function
• Brain disease that has occured as a result of liver disease (hepatic encephalopathy)
• Hereditary blood disorders called porphyrias
Not to be used in
• Known sensitivity or allergy to any ingredient
This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.
If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.
Pregnancy and Breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
• The safety of this medicine during pregnancy has not been fully established. It should only be used during pregnancy if considered essential by your doctor because no safer antibiotics are suitable or available. High dosage regimens should be avoided. Seek medical advice from your doctor.
• This medicine passes into breast milk. It should be used with caution in breastfeeding mothers and only if the expected benefit to the mother is greater than any possible risk to the nursing infant. High dosage regimens should be avoided unless the mother stops breastfeeding during the course. Seek medical advice from your doctor.
• Take this medication with or after food.
• This medication is to be swallowed whole, not chewed.
• This medication is to be taken with plenty of water.
• Avoid alcoholic drink whilst taking this medication.
• Take at regular intervals. Complete the prescribed course unless otherwise directed.
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.
• Disturbances of the gut such as diarrhoea, constipation, nausea, vomiting or abdominal pain
• Unpleasant taste
• Sensation of a furry tongue
• Inflamed and sore mouth
• Loss of appetite
• Itchy rash (urticaria)
• Severe swelling of lips, face or tongue (angioedema)
• Shaky movements and unsteady walk (ataxia)
• Skin rashes
• Pain in the muscles or joints
• Darkening of the urine
• Visual disturbances
• Liver disorders
• Disorder of the peripheral nerves called peripheral neuropathy, that causes weakness and numbness (on prolonged or intensive therapy)
• Decrease in the number of white blood cells in the blood (leucopenia)
The side effects listed above may not include all of the side effects reported by the drug's manufacturer.
For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
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 taking this one, to ensure that the combination is safe.
You should avoid alcohol while taking 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:
• ciclosporin (people taking ciclosporin may need their ciclosporin blood level and kidney function monitored while taking a course of metronidazole)
• fluorouracil (also known as 5-FU, this is an anticancer medicine; its side effects are increased by metronidazole, but not its anti-cancer effects)
• lithium (people taking lithium should have their lithium blood level and kidney function monitored while taking a course of metronidazole)
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.