Amotrex 400 mg Tablet (Metronidazole) – ACI Limited

1. About Amotrex 400 mg Tablet (Metronidazole)

Amotrex 400 mg Tablet contains Metronidazole 400 mg, a first-line nitroimidazole antibiotic and antiprotozoal agent manufactured by ACI Limited, Bangladesh. The 400 mg formulation is the most commonly prescribed strength for adult dosing in standard treatment regimens including amoebiasis, giardiasis, bacterial vaginosis, trichomoniasis, anaerobic infections, and Helicobacter pylori eradication.

Metronidazole is on the WHO Essential Medicines List and has been in clinical use since 1959. In Bangladesh, metronidazole 400 mg is a cornerstone antimicrobial used across general practice, gastroenterology, gynaecology, dentistry, and surgery. ACI Limited's Amotrex 400 mg provides cost-effective, GMP-standard access to this critical antiprotozoal-antianaerobic agent.

2. Mechanism of Action

Metronidazole is a prodrug requiring intracellular activation in anaerobic organisms:

• Selective reductive activation: Inside anaerobic bacteria and protozoa, low-redox electron transport proteins (ferredoxin, pyruvate:ferredoxin oxidoreductase) reduce metronidazole's nitro group, generating cytotoxic radical anions.
• DNA strand breakage: These reactive intermediates intercalate with DNA and cause irreversible strand breaks and helix disruption — rapidly killing the organism.
• Selective toxicity: Aerobic host cells cannot activate metronidazole (they lack the necessary low-redox proteins), making the drug selectively lethal to anaerobic pathogens while sparing human tissues.
• Broad anaerobic and antiprotozoal spectrum: Active against Bacteroides fragilis, Fusobacterium, Clostridium (including C. difficile), Prevotella, Entamoeba histolytica, Giardia lamblia, Trichomonas vaginalis, and H. pylori (synergistically with other agents).

3. Indications

Amotrex 400 mg Tablet (Metronidazole) is indicated for:

• Amoebiasis: Intestinal amoebiasis (amoebic dysentery), amoebic liver abscess — the 400 mg three-times-daily dose is the standard adult regimen
• Giardiasis: Giardia lamblia infection — highly prevalent in Bangladesh due to water contamination
• Bacterial Vaginosis (BV): First-line treatment with 400 mg twice daily for 7 days
• Trichomoniasis: 400 mg twice daily for 7 days or 2g single-dose regimen (treat partner concurrently)
• Helicobacter pylori Eradication: Triple therapy with amoxicillin + PPI for peptic ulcer disease and H. pylori gastritis
• Anaerobic Bacterial Infections: Intra-abdominal sepsis, pelvic inflammatory disease, peritonitis, brain abscess, lung abscess
• Pseudomembranous Colitis (C. difficile): First-line oral therapy for mild-moderate disease
• Dental and Oral Infections: Acute necrotising ulcerative gingivitis (ANUG), pericoronitis, dental abscess
• Surgical Prophylaxis: Colorectal and gynaecological surgery prophylaxis
• Diabetic Foot Infections: Combination therapy covering anaerobic component of polymicrobial diabetic foot infection

4. Dosage and Administration

Amoebiasis (intestinal/liver abscess):

• Adults: 400–800 mg 3 times daily for 5–10 days
• Children: 35–50 mg/kg/day in 3 divided doses for 5–10 days

Giardiasis:

• Adults: 400 mg 3 times daily for 5 days, or 2 g as single daily dose for 3 days

Bacterial Vaginosis:

• Adults: 400 mg twice daily for 7 days

Trichomoniasis:

• 2 g single dose (both partners), or 400 mg twice daily for 7 days

H. pylori Eradication:

• Adults: 400 mg twice daily for 7–14 days (+ amoxicillin 1g BD + omeprazole 20mg BD)

Anaerobic Infections:

• Adults: 400 mg every 8 hours for 7–14 days (severity-dependent)

Surgical Prophylaxis:

• Adults: 400 mg 2 hours pre-op, then 400 mg 8-hourly for 24 hours post-op

Administration: Take with or after food to minimise nausea. Do NOT consume alcohol during treatment or for 48 hours after last dose.

5. Contraindications

• Hypersensitivity to metronidazole or other nitroimidazoles
• First trimester of pregnancy — avoid unless essential
• Concurrent disulfiram use within 2 weeks — risk of acute psychosis
• Alcohol consumption — severe disulfiram-like reaction (absolute contraindication)

6. Warnings and Precautions

⚠ ALCOHOL ABSOLUTE CONTRAINDICATION: Any alcohol — even in small amounts — during metronidazole therapy or within 48 hours after the last dose causes a severe disulfiram-like reaction: violent nausea, vomiting, facial flushing, sweating, tachycardia, and headache. Alcohol includes all beverages, mouthwashes, cough syrups, or tonics containing ethanol.

Peripheral Neuropathy: Prolonged or high-dose use can cause peripheral neuropathy. Diabetic patients with pre-existing diabetic peripheral neuropathy are particularly vulnerable — any new numbness, tingling, or burning in extremities during treatment requires immediate medical review.

CNS Toxicity: High doses may cause seizures, encephalopathy, and cerebellar dysfunction. Use with caution in patients with CNS disease or epilepsy.

Hepatic Impairment: Extensive hepatic metabolism — reduce dose by one-third to one-half in severe liver disease.

Diabetes: No direct glycaemic effect. Diabetic patients with renal impairment may accumulate metronidazole metabolites — use shorter courses where possible. Pre-existing diabetic neuropathy is a relative caution for prolonged treatment.

Pregnancy and Lactation: Avoid in first trimester. May be used in 2nd/3rd trimester when essential. Metronidazole passes into breast milk — temporarily discontinue breastfeeding during and for 12–24 hours after single high-dose treatment.

7. Side Effects

Very common:

• Nausea — take with food to minimise
• Metallic or bitter taste (characteristic of metronidazole — harmless, temporary)

Common:

• Vomiting, diarrhoea, abdominal pain
• Headache, dizziness
• Dry mouth, furring of tongue, glossitis
• Dark (brown-red) discolouration of urine — harmless

Uncommon:

• Peripheral neuropathy (longer courses)
• Transient leukopenia
• Skin rash, urticaria, pruritus

Rare/Serious:

• Seizures, encephalopathy (high dose)
• Cerebellar ataxia, nystagmus, dysarthria
• Severe allergic reactions (anaphylaxis)
• Stevens-Johnson syndrome (very rare)

8. Drug Interactions

• Alcohol: Severe disulfiram-like reaction — absolute contraindication
• Warfarin: CYP2C9 inhibition markedly raises warfarin levels and INR — serious bleeding risk. Monitor INR and reduce warfarin dose.
• Disulfiram: Acute psychosis/confusional state — allow 2-week washout
• Phenytoin: Increased phenytoin levels and toxicity
• Phenobarbitone/Rifampicin: Accelerate metronidazole metabolism — reduced efficacy
• Lithium: Reduced renal clearance of lithium — toxicity risk
• 5-Fluorouracil: Increased 5-FU toxicity
• Ciclosporin: May increase ciclosporin blood levels

9. Pharmacokinetics

Absorption: Well absorbed orally; bioavailability ~80–100%. Tmax ~1–2 hours. Food delays absorption slightly without affecting extent.

Distribution: Excellent tissue penetration including CSF, brain, abscess cavities, bile, bone, and genital secretions. Plasma protein binding ~20%. Vd ~0.6–0.7 L/kg.

Metabolism: Extensively metabolised by hepatic CYP3A4 and other enzymes. Active hydroxy metabolite (~30% of parent activity) + glucuronide conjugates.

Elimination: Renal (60–80%) and faecal (6–15%). Terminal half-life ~6–9 hours. Prolonged in severe hepatic impairment. No significant accumulation with standard dosing in normal renal function.

10. Metronidazole 400 mg in Common Clinical Scenarios

The 400 mg strength is the most versatile form, enabling twice-daily and three-times-daily dosing for major indications:

• Amoebic liver abscess (400 mg × 3 daily × 10 days) — highly effective without drainage in most cases
• Bacterial vaginosis (400 mg × 2 daily × 7 days) — equivalent efficacy to topical gel with better compliance
• H. pylori triple therapy (400 mg × 2 daily with amoxicillin + PPI) — used where clarithromycin resistance is suspected; metronidazole-based triple therapy has good outcomes in Bangladesh
• Post-colorectal surgery prophylaxis — reduces anaerobic wound infection rate by 80%
• Diabetic foot infection — standard combination with cephalosporin (or fluoroquinolone) + metronidazole covers both aerobic gram-negative rods and anaerobes in polymicrobial infection

11. Antiprotozoal Infections in Bangladesh — Metronidazole Importance

Bangladesh has high prevalence rates of intestinal protozoan infections. Metronidazole 400 mg remains the first-line treatment:

• Entamoeba histolytica: Standard treatment — 400–800 mg × 3 daily × 5–10 days. Completion with a luminal agent (diloxanide furoate 500 mg × 3 daily × 10 days) is recommended to eliminate cysts and prevent relapse.
• Giardia lamblia: 400 mg × 3 daily × 5 days — cure rates ~90–95% in Bangladesh studies. Single-dose tinidazole is an alternative.

12. ACI Limited — Amotrex Range

ACI Limited's Amotrex range provides metronidazole in all required formulations for comprehensive clinical coverage:

• Amotrex 200 mg Tablet — paediatric and lower-dose adult regimens
• Amotrex 400 mg Tablet — standard adult dosing (this product)
• Amotrex 200 mg/5 ml Oral Suspension — paediatric liquid formulation
• Amotrex IV 500 mg/100 ml — intravenous infusion for hospitalised patients and surgical prophylaxis

All ACI Limited products are manufactured to WHO-GMP standards at DGDA-licensed facilities in Bangladesh.

13. Storage

• Store below 30°C in a cool, dry place
• Protect from direct sunlight and moisture
• Keep in original strip/box until use
• Keep out of reach of children
• Do not use after expiry date

Frequently Asked Questions (FAQ)

Q1: What is Amotrex 400 mg (Metronidazole 400 mg) used for?

Amotrex 400 mg is used for a wide range of infections caused by anaerobic bacteria and protozoa. The most common uses in Bangladesh are: amoebiasis (amoebic dysentery and liver abscess), giardiasis, bacterial vaginosis, trichomoniasis, H. pylori eradication (triple therapy for peptic ulcers), anaerobic bacterial infections (abdominal, pelvic, dental), and as part of combination antibiotic therapy for diabetic foot infections. The 400 mg tablet is the standard adult formulation — taken 2 or 3 times daily depending on the indication.

Q2: Why must I avoid alcohol with Amotrex 400 mg?

Metronidazole blocks the breakdown of acetaldehyde (an alcohol metabolite) in the body, causing a toxic accumulation that results in a severe reaction even with small amounts of alcohol. Symptoms include intense nausea, vomiting, flushing, sweating, rapid heartbeat, and severe headache. This disulfiram-like reaction is the same reaction used in alcohol aversion therapy. It can happen with any alcohol — beverages, mouthwash, cough syrups. Avoid all alcohol during the full course AND for 48 hours after the last tablet.

Q3: How long should I take Amotrex 400 mg?

Duration depends on the infection being treated: Amoebiasis — 5–10 days; Giardiasis — 5 days; Bacterial vaginosis — 7 days; Trichomoniasis — 7 days (or 2g single dose); H. pylori triple therapy — 7–14 days; Anaerobic infections — 7–14 days depending on severity. Always complete the full prescribed course even if you feel better earlier — stopping too soon can lead to treatment failure and antibiotic resistance.

Q4: Does Amotrex 400 mg affect blood sugar in diabetic patients?

Metronidazole does not directly affect blood glucose levels. However, diabetic patients should note: (1) Pre-existing diabetic peripheral neuropathy can be worsened by metronidazole — report any new numbness or tingling immediately. (2) Diabetic patients with kidney disease may accumulate metronidazole metabolites — your doctor may prescribe a shorter course. (3) Nausea and vomiting from metronidazole can reduce food intake and affect blood glucose management — monitor glucose more closely during treatment. Always inform your doctor of your diabetes status and medications before taking metronidazole.