Schedule H

Oral, Intravenous, Rectal, Topical (local use only)

Form Strengths Available

Tablet 200 mg, 400 mg

Injection (IV infusion) 500 mg/100 mL

Oral Suspension 200 mg/5 mL

Topical Gel/Cream/Lotion 0.75%, 1%

Suppository & Pessary 500 mg

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India)

1. Anaerobic Bacterial Infections

(Intra-abdominal infections, pelvic infections, brain abscess, anaerobic sepsis, aspiration pneumonia)

Parameter Oral Intravenous

Starting dose 400–500 mg every 8 hours 500 mg every 8 hours (infuse over 30–60 min)

Titration Not applicable Not applicable

Usual maintenance dose 400–500 mg every 8 hours 500 mg every 8 hours

Maximum dose 4 g/day 4 g/day

Duration 5–14 days depending on site 5–14 days depending on site

1. Amoebiasis (Intestinal or Hepatic)

Parameter Details

Starting dose 400–800 mg orally three times daily

Titration Not applicable

Usual maintenance dose 400–800 mg orally three times daily

Maximum dose 2.4 g/day

Duration 5–10 days

Clinical Notes:

• Follow with luminal agent (e.g., diloxanide furoate) after completing systemic therapy for invasive amoebiasis

• Severe hepatic abscess: May require IV metronidazole initially before oral switch

1. Giardiasis

Parameter Details

Starting dose 400–500 mg orally every 8 hours

Titration Not applicable

Usual maintenance dose 400–500 mg orally every 8 hours

Maximum dose 1.5 g/day

Duration 5–7 days

1. Trichomoniasis (Genital)

Option A — Single-Dose Regimen:

Parameter Details

Starting dose 2 g orally as single dose

Titration Not applicable

Usual maintenance dose Single dose only

Maximum dose 2 g

Option B — Multi-Day Regimen:

Parameter Details

Starting dose 400–500 mg orally twice daily

Titration Not applicable

Usual maintenance dose 400–500 mg orally twice daily

Maximum dose 1 g/day

Duration 5–7 days

Clinical Note: Treat both sexual partners simultaneously

1. Bacterial Vaginosis

Parameter Oral Vaginal

Starting dose 400–500 mg twice daily Vaginal gel 0.75% once daily

Titration Not applicable Not applicable

Usual maintenance dose 400–500 mg twice daily Once daily application

Maximum dose 1 g/day (oral) As per product insert

Duration 7 days 5 days

1. Clostridioides difficile Colitis (Mild-Moderate Cases)

Parameter Details

Starting dose 400–500 mg orally every 8 hours

Titration Not applicable

Usual maintenance dose 400–500 mg orally every 8 hours

Maximum dose 1.5 g/day

Duration 10 days

Clinical Note: Vancomycin or fidaxomicin preferred for severe or recurrent cases

Secondary Indications — Adults (Off-label)

PAEDIATRIC DOSING (Specialist Only)

Primary Indications

1. Amoebiasis / Giardiasis

Weight/Age Dose Frequency Duration Max Dose

All paediatric 30–50 mg/kg/day Divided into 3 doses 5–10 days 2.4 g/day

1. Anaerobic Infections

Phase Dose Route Frequency Max Single Dose

Loading 15 mg/kg IV over 30–60 min Once 500 mg

Maintenance 7.5 mg/kg IV or Oral Every 8 hours 500 mg

Safety Monitoring:

• Monitor for CNS toxicity if therapy exceeds 10 days

• Baseline and periodic liver function assessment

1. Clostridioides difficile (Mild Cases — Older Children)

Parameter Details

Dose 7.5 mg/kg/dose orally three times daily

Duration 10 days

Note Not first-line — consult paediatric infectious disease specialist

Minimum Age Statement

⚠️ Use with caution in infants <1 year — specialist supervision mandatory

Secondary Indications — Paediatrics (Off-label)

Indication Dose Notes

Neonatal surgical sepsis (anaerobic cover) 7.5 mg/kg IV every 12–24 hours (neonatal dosing) OFF-LABEL; NICU/Paediatric ID guidance only

H. pylori eradication Not commonly used Alternatives preferred in Indian paediatric practice

Mild-Moderate impairment No dose adjustment required

Severe impairment (CrCl <10 mL/min) Extend dosing interval to every 12 hours

Haemodialysis Administer dose after dialysis session

Peritoneal dialysis No supplemental dose required

• Known hypersensitivity to metronidazole or other nitroimidazoles

• Concurrent disulfiram use (within 2 weeks)

• Active CNS disease with risk of seizures or encephalopathy

• First trimester pregnancy for non-life-threatening indications (systemic use)

• Concurrent alcohol consumption

• History of seizures or neurological disorders

• Prolonged therapy (>10–14 days) — increased risk of peripheral neuropathy

• Pre-existing blood dyscrasias

• Candida overgrowth risk with prolonged courses

• Patients on anticoagulant therapy

• Elderly with impaired renal or hepatic reserve

Aspect Details

Overall Safety Category B — Generally considered safe in 2nd and 3rd trimesters

First Trimester Avoid high-dose or prolonged systemic use; topical/vaginal acceptable

When May Be Used Only when benefit clearly outweighs risk; invasive amoebiasis, severe anaerobic infection

Preferred Alternatives Tinidazole may be considered as alternative (similar safety profile)

Monitoring Fetal growth (prolonged courses); maternal GI tolerance

Aspect Details

Compatible with Breastfeeding Yes — compatible at standard doses

Milk Levels Low; approximately 10–20% of maternal plasma concentration

Preferred Alternatives None required at standard dosing

Infant Monitoring Bitter taste in milk may affect feeding; monitor feeding tolerance and stool changes

Aspect Recommendation

Starting dose Begin at lower end of dose range

Titration Slower titration if prolonged therapy anticipated

Special Risks Increased risk of CNS effects (confusion, dizziness); falls risk; slower hepatic/renal clearance

Duration Avoid prolonged courses (>7–10 days) unless clearly indicated

Interacting Drug Mechanism/Effect Management

Alcohol (ethanol) Disulfiram-like reaction (flushing, nausea, tachycardia) Avoid during therapy and for 48 hours after last dose

Disulfiram Acute psychosis, confusional states Contraindicated — do not co-administer

Warfarin CYP2C9 inhibition → increased INR and bleeding risk Reduce warfarin dose; increase INR monitoring frequency

Lithium Reduced lithium clearance → toxicity Monitor lithium levels closely

Phenytoin Inhibits phenytoin metabolism → increased phenytoin levels Monitor phenytoin levels and toxicity signs

Interacting Drug Effect Management

Cimetidine Reduces metronidazole clearance Monitor for increased side-effects

Rifampicin Induces metronidazole metabolism → reduced efficacy Consider dose increase or alternative

Cyclosporine May increase cyclosporine levels Monitor cyclosporine levels and creatinine

Carbamazepine Increased CNS side-effects Monitor for neurotoxicity

Busulfan Increased busulfan toxicity risk Avoid combination or monitor closely — haematology input

• Metallic or bitter taste (very common)

• Nausea, vomiting, anorexia

• Abdominal discomfort, diarrhoea

• Headache, dizziness

• Darkened urine (harmless chromogenic metabolite)

• Vaginal candidiasis (with prolonged use)

• Dry mouth

Adverse Effect Clinical Action

Peripheral neuropathy (paraesthesia, numbness) Discontinue immediately — may be irreversible

Seizures / Encephalopathy Discontinue; supportive care; more common with high doses or hepatic impairment

Stevens-Johnson Syndrome / TEN Stop immediately; dermatology/burns unit referral

Neutropenia / Agranulocytosis Monitor CBC; discontinue if confirmed

Optic neuropathy Rare; discontinue and ophthalmology referral

During therapy Neurological assessment (numbness, paraesthesia, seizures); GI tolerance

If on warfarin INR within 3–5 days of initiation and weekly thereafter

Prolonged therapy (>10 days) Repeat CBC; clinical assessment for neuropathy

Renal impairment Creatinine monitoring

Brand Name Manufacturer

Flagyl® Abbott

Metrogyl® J.B. Chemicals (Unique)

Aristogyl® Aristo

Metron® Pfizer

Aldezol® Alkem

Generic metronidazole Multiple manufacturers

FDC combinations available: With diloxanide furoate, norfloxacin, ofloxacin, simethicone

NLEM Status: Included in NLEM 2022 — NPPA ceiling price applicable

1. Counsel patients proactively about metallic taste — it is harmless but often causes non-compliance if unexpected

1. Zero alcohol rule: Emphasise complete avoidance during and 48 hours after therapy to prevent disulfiram-like reaction

1. Luminal agent mandatory: Always follow systemic amoebiasis treatment with diloxanide furoate or paromomycin to eradicate cyst carriage

1. Duration discipline: Limit courses to ≤10–14 days whenever possible to minimise peripheral neuropathy risk

1. Topical ≠ systemic: Topical metronidazole (for rosacea, wound care) does not achieve systemic levels — cannot treat systemic infections

1. C. difficile hierarchy: Reserve metronidazole for mild cases only; oral vancomycin/fidaxomicin preferred for severe or recurrent episodes

metronidazole; anaerobic infections; amoebiasis; giardiasis; trichomoniasis; bacterial vaginosis; H. pylori; nitroimidazole; NLEM India; pregnancy-compatible

RxIndia v1.0 — 28 Apr 2025

• CDSCO product information

• Indian Pharmacopoeia

• NLEM (2022)

• ICMR Treatment Guidelines for Antimicrobial Use

• API Textbook of Medicine

• AIIMS Antibiotic Policy (Intra-abdominal & Anaerobic Infections)

• IAP Pediatric Infectious Disease Module

• WHO EML (supportive for paediatric dosing)

• Harrison's Principles of Internal Medicine