Introduction
Metronidazole is a nitroimidazole antimicrobial agent with a unique dual role in both human and veterinary medicine. It is one of the most widely used antibiotics worldwide, listed on the WHO Model List of Essential Medicines, and remains a first-line treatment for anaerobic bacterial infections and protozoal diseases. Its versatility across both human pharmaceutical and veterinary applications makes Metronidazole API one of the most consistently demanded bulk pharmaceutical ingredients in global trade.
This guide provides pharmaceutical manufacturers, veterinary drug producers, and bulk buyers with a thorough understanding of Metronidazole API — its chemical properties, mechanism of action, quality specifications, dosage forms, and best practices for sourcing from Chinese GMP-certified manufacturers.
Quick Facts: Metronidazole (CAS No. 443-48-1) was first introduced in 1960 and is used in over 100 countries. Global annual production exceeds 3,000 metric tons. China and India are the primary producers, with China manufacturing the majority of the bulk API for global export. Metronidazole is approved for both human and veterinary use, making it one of the few APIs with truly cross-species applications.
Chemical Profile & Identification
Metronidazole belongs to the 5-nitroimidazole class of antimicrobial agents. Its chemical structure features a nitro group that is essential for its antimicrobial activity.
| Property | Value |
|---|---|
| INN Name | Metronidazole |
| CAS Number | 443-48-1 |
| Molecular Formula | C₆H₉N₃O₃ |
| Molecular Weight | 171.15 g/mol |
| Appearance | White to pale yellow crystalline powder |
| Solubility | Slightly soluble in water; soluble in alcohol; slightly soluble in ether and chloroform |
| pKa | 2.55 |
| Melting Point | 159–163°C |
| Storage Condition | Protect from light, store in well-closed containers |
Mechanism of Action
Metronidazole's antimicrobial activity is unique among antibiotics and relies on a mechanism that distinguishes it from beta-lactams, fluoroquinolones, and other classes:
- Selective Uptake: Metronidazole is a prodrug that is selectively taken up by anaerobic bacteria and protozoa. Aerobic organisms lack the transport mechanism needed for significant intracellular accumulation.
- Intracellular Activation: Inside the target organism, metronidazole's nitro group is reduced by pyruvate:ferredoxin oxidoreductase (PFOR) and other low-redox-potential electron transport proteins, producing reactive intermediates (nitroso, hydroxylamine, and free radical species).
- DNA Damage: These reactive intermediates bind to and break bacterial DNA strands, inhibiting DNA replication and transcription, ultimately causing cell death.
This selective activation mechanism means metronidazole is inactive against most aerobic bacteria but highly effective against anaerobes, making it the drug of choice for mixed anaerobic-aerobic infections when combined with other antibiotics.
Spectrum of Activity
- Anaerobic Bacteria: Bacteroides fragilis, Fusobacterium spp., Clostridium difficile, Peptostreptococcus spp., Prevotella spp.
- Protozoa: Giardia lamblia (giardiasis), Trichomonas vaginalis (trichomoniasis), Entamoeba histolytica (amebiasis)
- Helicobacter pylori: Used as part of triple/quadruple therapy regimens for H. pylori eradication (combined with amoxicillin and a PPI)
Veterinary Note: In veterinary medicine, metronidazole is widely used to treat giardiasis in dogs and cats, anaerobic infections in horses and ruminants, and certain protozoal infections in poultry. It is one of the most commonly dispensed antimicrobials in small animal veterinary practice worldwide.
Quality Standards & Specifications
Metronidazole API must meet rigorous pharmacopoeial standards. The three major pharmacopoeias each publish detailed monographs with specific requirements:
USP (United States)
- Assay: 97.0–103.0%
- Related substances: ≤0.5% (individual)
- Water: ≤0.5%
- Residue on ignition: ≤0.1%
- Heavy metals: ≤20 ppm
BP (UK/Commonwealth)
- Assay: 99.0–101.0%
- Related substances: ≤0.25% (any individual)
- Water: ≤0.5%
- Sulfated ash: ≤0.1%
- Appearance of solution: clear
EP (European)
- Assay: 99.0–101.0%
- Impurity A: ≤0.15%
- Impurity B: ≤0.10%
- Water: ≤0.5%
- Any other impurity: ≤0.05%
Key Quality Parameters
- Assay: The purity of metronidazole must fall within the pharmacopoeial range. HPLC is the standard analytical method with a reference standard.
- Related Substances: Common impurities include 2-methyl-5-nitroimidazole (impurity A), 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole (impurity B), and acetamide derivatives. These must be tightly controlled as they may affect safety and tolerability.
- Water Content: Metronidazole should be essentially anhydrous (≤0.5%). Karl Fischer titration is the standard test method.
- Particle Size: D50 typically 30–80 µm; important for direct compression tablet manufacturing and uniform content in suspension formulations.
- Melting Point: 159–163°C — serves as a quick identity and purity verification test.
Pharmaceutical Applications
Metronidazole's versatility across human and veterinary medicine creates strong demand from both pharmaceutical sectors:
Human Dosage Forms
| Dosage Form | Common Strengths | Primary Indications |
|---|---|---|
| Oral Tablets | 200mg, 250mg, 400mg, 500mg | Bacterial vaginosis, amebiasis, giardiasis, anaerobic infections |
| Oral Capsules | 375mg | Bacterial vaginosis, PID (pelvic inflammatory disease) |
| Oral Suspension | 125mg/5mL, 200mg/5mL | Pediatric infections, giardiasis |
| IV Infusion | 500mg/100mL | Severe anaerobic infections, intra-abdominal sepsis |
| Vaginal Gel | 0.75%, 1.0% | Bacterial vaginosis |
| Topical Cream/Gel | 0.75%, 1.0% | Rosacea, infected dermatitis |
| Suppositories | 500mg, 1g | Rectal anaerobic infections, protozoal diseases |
Veterinary Applications
| Species | Common Conditions | Dosage Form |
|---|---|---|
| Dogs & Cats | Giardiasis, periodontal infections, anaerobic abscesses, inflammatory bowel disease | Tablets, oral suspension |
| Horses | Anaerobic infections, peritonitis, clostridial enterocolitis | Oral paste, IV injection |
| Cattle & Sheep | Bovine trichomoniasis, anaerobic mastitis | Bolus, oral drench |
| Poultry | Histomoniasis (blackhead disease), giardiasis | Feed additive, drinking water solution |
| Aquaculture | Protozoal infections in fish and shrimp | Feed premix |
Market Opportunity: The dual human-veterinary application of metronidazole makes it particularly attractive for API buyers who serve both markets. A single API qualification can support multiple product lines, reducing overall procurement complexity and costs.
Procurement Guide
1. Selecting a Metronidazole API Supplier
- Verify NMPA GMP certification covering metronidazole production
- Check for WHO-PQ listing or international regulatory filings (US FDA DMF, EDQM CEP) — particularly important if you target regulated markets
- Confirm the supplier's annual production capacity — reliable Chinese manufacturers produce 200+ MT per year
- Request stability data under ICH conditions (25°C/60%RH and 40°C/75%RH) to confirm shelf life claims
- Evaluate the supplier's ability to provide both human-grade and veterinary-grade metronidazole if you serve both sectors
2. Sample Evaluation
- Request a 500g–1kg evaluation sample with complete COA and GMP certificate
- Test against your target pharmacopoeial standard (USP/BP/EP)
- Key analytical tests: HPLC assay, related substances (individual and total), water content (Karl Fischer), particle size distribution, residual solvents
- Conduct dissolution testing if planning tablet formulation — metronidazole has low aqueous solubility and particle size significantly impacts dissolution rate
3. Pricing Overview
Market Reference: Metronidazole API (pharmaceutical grade, ≥99.0% purity) typically trades at USD 8–15/kg FOB China, making it one of the most affordable antibiotics on the market. Pricing varies based on order volume, particle size specification, and target pharmacopoeial standard. Veterinary-grade material may be priced 10–20% lower than human-grade. Contact us for current pricing.
4. Required Documentation
- Certificate of Analysis (COA) — per batch, including HPLC chromatograms for related substances
- GMP Certificate — valid, product-specific certificate
- MSDS/SDS — for transport, handling, and customs clearance
- Certificate of Origin — for import documentation
- DMF reference — if supplier has active DMF filings for US/EU markets
- Stability data summary — accelerated and long-term stability results
Storage & Handling
- Temperature: Store below 25°C in a dry, well-ventilated area
- Light Protection: Store in light-resistant containers; metronidazole is photosensitive and may develop a yellow tint upon prolonged light exposure (does not affect potency)
- Packaging: 25kg fiber drums with double PE inner liners
- Shelf Life: Typically 36 months from manufacture date when stored correctly
- Handling: Standard PPE recommended; avoid inhalation of dust. Not classified as a hazardous substance under GHS, but good industrial hygiene practices apply
Regulatory Warning: Metronidazole is classified as a suspected carcinogen (Group B2 by US EPA) based on animal studies. This classification primarily affects environmental regulations and occupational exposure limits. It does not impact its approved therapeutic use in human or veterinary medicine, but should be noted for manufacturing and waste disposal compliance.
Key Takeaways
- Metronidazole is a versatile nitroimidazole antibiotic effective against anaerobic bacteria and protozoa, approved for both human and veterinary use
- Its unique mechanism of action (intracellular nitro group reduction) provides selective activity against anaerobic organisms
- Quality must meet pharmacopoeial standards (USP/BP/EP) — related substances and water content are critical parameters
- China is the dominant global producer, offering competitive pricing (USD 8–15/kg) from GMP-certified manufacturers
- The dual human-veterinary application makes metronidazole an efficient API to qualify for companies serving both sectors
- Always request evaluation samples, conduct independent testing, and verify GMP certificates before placing commercial orders
Ready to Source Metronidazole API?
CN-ConnectWorld supplies pharmaceutical-grade Metronidazole API (≥99.0% purity, BP/USP/EP standard) for both human and veterinary use. GMP certified. COA, MSDS, and GMP certificates provided. MOQ 1kg, sample available.