Flagyl 400mg Tablet (Metronidazole)

Drug Class: Nitroimidazole Antibiotic & Antiprotozoal | Form: Oral Tablet | Prescription Status: Prescription Only (Rx) — DRAP Registered

What is Flagyl 400mg Tablet?

Flagyl 400mg Tablet contains Metronidazole — a powerful antibiotic and antiprotozoal medicine that belongs to the nitroimidazole class. Unlike most antibiotics that only fight bacteria, Metronidazole has a uniquely broad action — it is effective against both harmful bacteria (بیکٹیریا) and parasites (پرجیوی) that cause infections in multiple parts of the body simultaneously.

Flagyl 400mg is one of the most widely prescribed medicines in Pakistan for treating infections of the intestines, stomach, genital tract, mouth, and other organs caused by anaerobic bacteria — bacteria that thrive in low-oxygen environments — and by protozoan parasites such as amoeba and Giardia. It is particularly important in Pakistan's healthcare setting given the relatively high prevalence of parasitic gut infections such as amoebiasis and giardiasis in the community.

Because Metronidazole penetrates deeply into tissues — including the brain, lungs, bones, and blood — it is effective against infections in parts of the body that many other antibiotics struggle to reach. As with all antibiotics, the full prescribed course must always be completed even when symptoms improve before it ends.

What is Flagyl 400mg Tablet Used For?

Flagyl 400mg Tablet is approved for the treatment of the following bacterial and parasitic infections:

• Amoebiasis — infection caused by the parasite Entamoeba histolytica causing severe diarrhoea, bloody stools, and intestinal ulcers — very common in Pakistan (پیچش / آنتوں کا انفیکشن)
• Giardiasis — intestinal infection caused by the Giardia lamblia parasite causing persistent loose stools, bloating, and stomach cramps (گیارڈیا انفیکشن)
• Bacterial vaginosis — bacterial imbalance in the vagina causing abnormal discharge and odour (اندام نہانی کا بیکٹیریل انفیکشن)
• Trichomoniasis — sexually transmitted parasitic infection of the genital tract in both men and women (ٹرائیکومونیاس)
• Dental and oral infections — severe gum infections (periodontitis), tooth abscesses, and acute necrotising ulcerative gingivitis (دانتوں اور مسوڑھوں کا انفیکشن)
• Anaerobic bacterial infections — infections caused by bacteria that survive without oxygen, affecting the blood, brain, lungs, bones, abdomen, and genital tract
• Helicobacter pylori eradication — used as part of combination therapy to eradicate H. pylori bacteria causing stomach ulcers and gastritis (معدے کا السر)
• Intra-abdominal infections — peritonitis and other bacterial infections inside the abdominal cavity
• Brain abscess — bacterial abscess in brain tissue where Metronidazole's ability to penetrate the blood-brain barrier makes it one of very few effective options (دماغ کا پھوڑا)
• Bone and joint infections — anaerobic bacterial infections of bone and joint tissue
• Lung infections — anaerobic bacterial lung abscess and pleural infections
• Pseudomembranous colitis — serious gut infection caused by Clostridioides difficile bacteria

How Does Flagyl 400mg Tablet Work?

Metronidazole works through a unique and highly targeted mechanism that makes it effective against both anaerobic bacteria and protozoan parasites:

Once Flagyl 400mg is absorbed into the body and enters bacterial or parasitic cells, it undergoes a chemical activation process. Inside anaerobic organisms, Metronidazole is converted into a toxic reactive form that directly attacks and breaks apart the DNA of the bacteria or parasite. Without intact DNA, the organism cannot reproduce, repair itself, or survive — and it dies rapidly.

This mechanism has two important clinical implications:

Selectivity against anaerobes: The chemical activation of Metronidazole only occurs in low-oxygen (anaerobic) environments — meaning it selectively targets anaerobic bacteria and protozoa while having minimal effect on the aerobic (oxygen-dependent) bacteria that make up much of the body's normal flora. This makes it highly targeted for the specific organisms it is designed to treat.

Deep tissue penetration: Metronidazole is a small molecule with excellent ability to cross biological barriers — including the blood-brain barrier, placental barrier, and bone tissue. This allows it to reach and treat infections in the brain, lungs, bones, and abdominal cavity where many other antibiotics cannot achieve adequate concentrations.

After oral administration, Flagyl 400mg is rapidly and almost completely absorbed — reaching effective blood levels within 1 to 2 hours and distributing widely throughout all body tissues and fluids.

Dosage and Administration

⚠️ Always take exactly the dose prescribed by your doctor for the full duration of the course. Never stop taking this medicine early — even if you feel completely better — without your doctor's specific advice.

Paediatric Dosing:

• Dosing in children is calculated based on body weight — typically 7.5mg per kg of body weight per dose, given 3 times daily
• The paediatrician will calculate and prescribe the exact dose appropriate for the child's weight and condition
• Flagyl Suspension (syrup) is more appropriate for young children — the 400mg tablet is suitable for older children and adolescents under doctor's guidance

How to Take:

• Swallow the tablet whole with a full glass of water
• Always take with food or immediately after a meal — this significantly reduces the nausea and stomach upset that Metronidazole commonly causes when taken on an empty stomach
• Take doses at evenly spaced intervals — for example every 8 hours for a three-times-daily schedule — to maintain consistent blood levels of the medicine
• Do not crush or chew the tablet unless specifically advised by your doctor
• Complete the full prescribed course without exception

Active Ingredient

Who Should NOT Take Flagyl 400mg Tablet?

Do not take this tablet if you:

• Are allergic to Metronidazole or any other nitroimidazole medicine (such as Tinidazole or Ornidazole)
• Have a history of blood disorders or bone marrow suppression
• Are in the first trimester of pregnancy — Metronidazole should be avoided in the first 3 months of pregnancy
• Are currently taking Disulfiram (a medicine for alcohol dependence) or have taken it within the last 2 weeks — a dangerous interaction exists

Always consult your doctor before taking Flagyl 400mg if you have any of the following:

• Liver disease — Metronidazole is metabolised by the liver; severe liver disease requires dose reduction and careful monitoring
• Kidney disease — monitoring may be required during prolonged courses
• Neurological conditions — history of seizures, epilepsy, or other nervous system disorders
• Peripheral neuropathy — existing nerve damage in the hands or feet, as Metronidazole can worsen this with prolonged use
• Are regularly consuming alcohol — a severe and dangerous interaction exists (see below)
• Are pregnant (second or third trimester) or breastfeeding — use only when clearly indicated by a doctor
• Are taking blood-thinning medicines such as Warfarin

Side Effects

Flagyl 400mg is generally well tolerated at the prescribed dose for the recommended duration. Side effects are more common with higher doses or prolonged courses.

Common Side Effects:

• Nausea, stomach discomfort, or vomiting — most common side effect; significantly reduced by always taking with food
• Metallic or bitter taste in the mouth (منہ میں کڑوا ذائقہ) — very characteristic of Metronidazole; affects many patients but is harmless and temporary
• Loss of appetite
• Diarrhoea (دست) or stomach cramps
• Mild headache or dizziness
• Dark or reddish-brown urine — harmless discolouration caused by Metronidazole metabolites; not a sign of kidney problems
• Dry mouth or unpleasant breath

Serious Side Effects — Stop Taking and Seek Medical Attention Immediately:

• Neurological effects — numbness, tingling, or burning sensation in hands or feet (peripheral neuropathy); confusion, difficulty speaking, unsteady walking, or visual disturbances — stop immediately and contact your doctor
• Seizures or fits — particularly with high doses or in patients with pre-existing neurological conditions — seek emergency help immediately (یہ طبی ہنگامی صورتحال ہے)
• Severe allergic reaction — sudden widespread rash, swelling of the face, lips, tongue or throat, difficulty breathing
• Severe skin reaction — blistering, peeling, or raw areas of skin — rare but requires immediate emergency attention
• Signs of liver damage — yellowing of skin or eyes (یرقان / jaundice), dark urine, severe upper abdominal pain, unusual fatigue
• Signs of blood disorder — unusual bruising, persistent sore throat, fever, or severe and unexplained fatigue — rare but possible with prolonged use
• Worsening of existing nerve damage (neuropathy) — if you already have peripheral neuropathy, Metronidazole can worsen it with prolonged use; inform your doctor immediately if numbness or tingling worsens

If any serious side effect occurs, stop Flagyl 400mg immediately and go to the nearest hospital emergency department without delay.

Drug, Food, and Alcohol Interactions

Always inform your doctor and pharmacist about all medicines, supplements, and herbal products you are taking before starting Flagyl 400mg Tablet.

🚨 Critical Alcohol Warning: Patients taking Flagyl 400mg must completely avoid all forms of alcohol — including beverages, medicines, and foods containing alcohol — during the entire course of treatment and for a minimum of 48 hours after the last dose. This reaction can be sudden, severe, and medically dangerous.

Storage Instructions

• Store below 25°C in a cool, dry place
• Protect from direct sunlight and moisture
• Keep in the original packaging until time of use
• Keep out of reach of children (بچوں کی پہنچ سے دور رکھیں)
• Do not store in the bathroom or near a kitchen — humidity and heat can degrade the tablets
• Do not use after the expiry date printed on the blister pack or outer carton

Frequently Asked Questions

Why does Flagyl 400mg cause a metallic taste in the mouth?

The metallic or bitter taste (منہ میں دھاتی ذائقہ) is one of the most characteristic and commonly reported effects of Metronidazole. It is caused by the way Metronidazole and its metabolites interact with taste receptors on the tongue. It is completely harmless and temporary — disappearing within a day or two of completing the course. Drinking plenty of water, chewing sugar-free gum, or sucking on sugar-free mints can help manage the taste during treatment. Brushing teeth more frequently also helps some patients.

Why must alcohol be completely avoided while taking Flagyl 400mg?

Metronidazole blocks an enzyme called aldehyde dehydrogenase — the enzyme the body uses to break down alcohol after it is consumed. When alcohol is taken alongside Metronidazole, a toxic substance called acetaldehyde accumulates in the blood, causing an intensely unpleasant and potentially dangerous reaction including severe facial flushing, rapid heartbeat, nausea, vomiting, and a sharp drop in blood pressure. This is known as a disulfiram-like reaction and can be medically serious. Alcohol in any form — including drinks, syrups, mouthwashes, and some foods — must be completely avoided during treatment and for at least 48 hours after the last dose.

Can Flagyl 400mg treat both amoebiasis and giardiasis?

Yes — both amoebiasis and giardiasis are very common parasitic gut infections in Pakistan, and Metronidazole is a first-line treatment for both. Amoebiasis is caused by Entamoeba histolytica and typically presents with bloody diarrhoea, stomach cramps, and sometimes liver abscess. Giardiasis is caused by Giardia lamblia and causes persistent watery diarrhoea, bloating, and flatulence. Both parasites are susceptible to Metronidazole's DNA-disrupting mechanism. The dose and duration differ slightly — your doctor will prescribe the appropriate regimen based on the specific diagnosis confirmed by stool examination.

Is Flagyl 400mg safe during pregnancy?

Metronidazole should be avoided in the first trimester of pregnancy as a precautionary measure. In the second and third trimesters, it may be prescribed when a bacterial or parasitic infection clearly requires treatment and the benefit to the mother outweighs any potential risk. It should not be used as a single high dose during pregnancy. Always inform your doctor immediately if you are pregnant or suspect you may be pregnant before taking Flagyl 400mg. Your doctor will assess the safest treatment option for both you and your baby.

Why is it important to treat the sexual partner as well during trichomoniasis treatment?

Trichomoniasis is a sexually transmitted infection caused by a parasite that can be passed between sexual partners during intercourse. Even if the partner has no symptoms, they may carry and transmit the parasite. If only one partner is treated, re-infection from the untreated partner is almost certain. Both partners must complete the full prescribed course of Metronidazole simultaneously, and sexual contact should be avoided until both have completed treatment and symptoms have fully resolved. This is essential for successful treatment and prevention of recurrence.

Can I take Flagyl 400mg for a stomach ulcer?

Flagyl 400mg is not used alone for stomach ulcers. However, it is an important component of combination therapy for Helicobacter pylori eradication — the bacterial infection responsible for the majority of peptic ulcers and chronic gastritis. It is typically prescribed alongside another antibiotic (such as Clarithromycin or Amoxicillin) and a proton pump inhibitor (such as Omeprazole) as part of a 7 to 14-day triple or quadruple therapy regimen. Your gastroenterologist will prescribe the full combination based on your confirmed H. pylori status and local resistance patterns.

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⚕️ Medical Disclaimer: This product description is provided for general informational purposes only and does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified and licensed doctor or pharmacist before starting, stopping, or changing any prescription medicine. Complete the full prescribed course and avoid all alcohol during treatment and for 48 hours after the last dose. If symptoms worsen or do not improve, seek medical advice promptly.

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DRAP Registered | Prescription Required (Rx) | Always take with food — avoid all alcohol during treatment and 48 hours after — complete the full course