Metronidazole for bacterial infection
Flagyl
Revisione paritaria di Dr Colin Tidy, MRCGPUltimo aggiornamento di Michael Stewart, MRPharmSUltimo aggiornamento 26 Mar 2023
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Swallow metronidazole tablets with plenty of water. Take them with a meal or a snack.
Do not drink alcohol while you are taking metronidazole, and for 48 hours after finishing your course of treatment.
Space your doses evenly throughout the day, and keep taking the medicine until the course is finished.
The most common side effects of metronidazone are feeling sick (nausea) and being sick (vomiting).
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About metronidazole
Tipo di medicinale | Antimicrobial agent (antibiotic) |
Utilizzato per | To treat or prevent infection |
Chiamato anche | Flagyl® |
Disponibile come | Tablets, oral liquid medicine, suppositories, and injection |
What is metronidazole used for?
Torna ai contenutiMetronidazole is an antibiotico used to treat a wide variety of bacterial infections caused by anaerobic bacteria and types of micro-organisms called protozoa.
These types of organisms often cause infections in areas of the body such as the gums, pelvic cavity and tummy (stomach or intestines) because they do not need oxygen to grow and multiply.
Metronidazole is commonly prescribed to treat vaginosi batterica, and, is also prescribed before gynaecological surgery and surgery on the intestines, to prevent infection from developing.
Metronidazole is also used, alongside other medicines, to get rid of Helicobacter pylori, a bacterial infection often associated with stomach ulcers.
It can safely be taken by people who are allergic to penicillin.
Metronidazole is available as a skin preparation also. This leaflet does not give information about metronidazole when it is used for skin conditions, but there is more information available in a separate leaflet called Metronidazole skin gel and cream.
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Side effects of Metronidazole
Torna ai contenutiCommon side effects of metronidazole are:
Sensazione di nausea.
Vomito.
Changes in how things taste.
Furred tongue
Sore mouth.
Lack of appetite.
You will find a full list in the manufacturer's information leaflet supplied with your medicine.
Gli effetti indesiderati spesso migliorano man mano che il tuo corpo si adatta al nuovo medicinale, ma parla con il tuo medico o farmacista se uno dei seguenti persiste o diventa problematico.
How to manage metronidazole side effects
Torna ai contenutiMetronidazole side effects | Cosa posso fare se sperimento questo? |
Sentirsi male o essere malati | Stick to simple foods. Make sure you take your doses after a meal or a snack |
Changes in the way things taste, furred tongue, sore mouth | Ask your pharmacist to recommend a suitable mouthwash |
Mancanza di appetito | Questo dovrebbe passare presto, ma nel frattempo scegli cibi che di solito ti piacciono |
Se si verificano altri sintomi che ritieni possano essere dovuti a questo medicinale, parla con il tuo medico o farmacista.
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Who should not take metronidazole
Torna ai contenutiSome medicines aren’t suitable for certain health conditions or may require extra care. Before taking metronidazole, it is important to let your doctor know:
Se sei incinta o stai allattando.
If you feel you will be unable to stop drinking alcohol for the duration of your treatment.
Se hai problemi con il funzionamento del tuo fegato.
Se hai un raro disturbo ereditario del sangue chiamato porfiria.
Se stai assumendo altri medicinali. Questo include qualsiasi medicinale che stai assumendo e che è disponibile per l'acquisto senza prescrizione medica, così come i medicinali a base di erbe e complementari.
Se hai mai avuto una reazione allergica a un medicinale.
How to take metronidazole
Torna ai contenutiRead the information leaflet in your pack before starting. It explains metronidazole and lists possible side effects.
Take the tablets or liquid exactly as your doctor or dentist tells you. Your dose depends on the type and severity of your infection.
Adults often take 400 mg two or three times a day, but your dose may be different. Children’s doses depend on age and weight. You're doctor will tell you what dose to take.
Space your doses evenly throughout the day and finish the full course unless your doctor tells you to stop. Stopping early can make the infection come back.
Most courses of metronidazole last about seven days, but some can last anywhere from 3-14 days. For certain infections, you may be given one large dose, usually five 400 mg tablets (2 g),to take at once.
Take each of your doses with a snack or just after eating a meal. Swallow the tablets whole (that is, without chewing or crushing them) with a full glass of water.
If you forget to take a dose, take it as soon as you remember and try to space your remaining doses evenly throughout the rest of the day. Non assumere due dosi insieme to make up for a forgotten dose.
If you have been given metronidazole suppositories
Remove the suppository from its wrapping.
Using your finger, gently push the suppository into your back passage (rectum) as far as is comfortable. Many people find that inserting a suppository is easier if they squat or bend forward.
Remain still for a few moments to help you to hold the suppository in place.
Lavati le mani.
Ottenere il massimo dal tuo trattamento
Torna ai contenutiMetronidazole can make your urine look darker. This is usually harmless, but if you also get stomach pain, feel sick, or feel unwell, tell your doctor.
Check with a pharmacist before buying any other medicines. Some cold and cough products contain alcohol and shouldn’t be taken with metronidazole.
If you need to take metronidazole for more than 10 days, your doctor may arrange tests. Be sure to attend any appointments.
Importante: do not drink alcohol while you are on metronidazole and for 48 hours after finishing your course of treatment. This is because drinking alcohol with metronidazole is likely to make you feel very sick (nauseated) and cause other unpleasant effects, such as the sensation of having a 'thumping heart' (palpitations), hot flushes, and headache.
How to store metronidazole
Torna ai contenutiTenere tutti i medicinali fuori dalla portata e dalla vista dei bambini.
Conservare in un luogo fresco e asciutto, lontano da fonti di calore e luce diretta.
Informazioni importanti su tutti i medicinali
Torna ai contenutiInformazioni importanti su tutti i medicinali
Non assumere mai più della dose prescritta. Se sospetti che tu o qualcun altro possa aver assunto un sovradosaggio di questo medicinale, recati al pronto soccorso del tuo ospedale locale. Porta con te il contenitore, anche se è vuoto.
Se devi sottoporti a un'operazione o a un trattamento dentistico, informa la persona che esegue il trattamento sui medicinali che stai assumendo.
Questo medicinale è per te. Non darlo mai ad altre persone, anche se la loro condizione sembra essere la stessa della tua.
Non conservare mai medicinali scaduti o indesiderati. Portali alla tua farmacia locale che li smaltirà per te.
Se hai domande su questo medicinale, chiedi al tuo farmacista.
Segnala effetti collaterali di un medicinale o vaccino
Se si verificano effetti collaterali, è possibile segnalarli online tramite il Yellow Card website.
Domande frequenti
Torna ai contenutiHow long does it take for metronidazole to work?
Metronidazole usually starts to work within 1-2 days, with most people noticing an improvement in their symptoms after 48 hours. Always finish your course of treatment even if you are feeling better.
Is it safe to take metronidazole during pregnancy?
Yes, it is usually safe to take metronidazole during pregnancy if it is prescribed to you. However, always let your doctor know that you are pregnant before taking metronidazole.
Can you drink alcohol when taking metronidazole?
No, you should not drink alcohol if you are taking metronidazole as it can cause a strong reaction, including nausea, vomiting, flushing, headaches, and a fast heartbeat. You should wait until 2 days after your last dose before having alcohol.
How long does metronidazole stay in your system for?
Metronidazole stays in your system for about 2-3 days after your last dose. It has a half-life of around 8 hours, which means it takes about 8 hours for the amount of the drug in your bloodstream to reduce by half.

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Ulteriori letture e riferimenti
- Manufacturer's PIL, Flagyl® 200 mg and 400 mg Tablets; Sanofi, The electronic Medicines Compendium. Dated December 2021.
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About the author

Michael Stewart, MRPharmS
Medicine Leaflet Review Manager – Contractor, Pharmacist
BPharm (Hons), MRPharmS
Michael is a community pharmacist practicing in the Midlands and South Yorkshire with more than 20 years’ experience advising on medicines and medical conditions. He has a strong background in healthcare training, having produced and delivered training courses for pharmacy teams and staff of residential care settings, including nurses. He has also contributed to pharmacy advisory boards for the management of low acuity conditions in the community.
About the reviewerView full bio

Dr Colin Tidy, MRCGP
Medico di base, Autore medico
MBBS, MRCGP, MRCP (Paediatrics), DCH
Dr Colin Tidy is an NHS Doctor, based in Oxfordshire.
Storia dell'articolo
Le informazioni su questa pagina sono scritte e revisionate da clinici qualificati.
Prossima revisione prevista: 25 Set 2027
26 Mar 2023 | Ultima versione

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