Metronidazole chemical structure (nitroimidazole), 2D skeletal formula, C6H9N3O3

Metronidazole Chemical Structure

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1. Identification

Summary

Metronidazole is a nitroimidazole antibacterial/antiprotozoal used systemically and topically for susceptible anaerobic infections and select protozoal diseases.

Brand Names

Flagyl, Metrogyl, Metrogel/MetroCream (topical), Vandazole/Nuvessa (vaginal); generics common

Name

Metronidazole

Background

Synthetic 5-nitroimidazole introduced mid-20th century; oral, IV, topical (dermal), and intravaginal formulations are standard.

Modality

Small molecule

Groups

Approved; prescription

Structure

Metronidazole 2D chemical structure (5-nitroimidazole). Formula C6H9N3O3; IUPAC 2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol; CAS 443-48-1.
Metronidazole chemical structure (nitroimidazole), 2D skeletal formula, C6H9N3O3

Weight

~171.15 g/mol (base)

Chemical Formula

C₆H₉N₃O₃

Synonyms

2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol; 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole

External IDs

CAS: 443-48-1; PubChem CID: 4173; UNII: 140QMO216E; ATC (key codes): J01XD01, A01AB17, D06BX01, G01AF01, P01AB01

2. Pharmacology

Indication

Anaerobic bacterial infections (systemic/IV); bacterial vaginosis (oral/vaginal); trichomoniasis; intestinal/hepatic amebiasis; giardiasis; rosacea (topical).

Associated Conditions

Intra-abdominal, gynecologic, skin/soft-tissue, CNS, bone/joint infections due to susceptible anaerobes; dental/oral infections (local use).

Associated Therapies

Used with surgical source control for anaerobic sepsis; combined regimens for mixed aerobic–anaerobic infections per local guidance.

Contraindications & Blackbox Warnings

No boxed warning. Contraindicated with disulfiram within 2 weeks (neuropsychiatric reactions). Avoid alcohol during therapy and for ≥3 days after (reaction risk noted in labeling).

Pharmacodynamics

Prodrug; in anaerobic conditions the nitro group is reduced to reactive intermediates that damage DNA, yielding bactericidal/protozoacidal effects against susceptible organisms.

Mechanism of action

Intracellular electron transport proteins (e.g., ferredoxin) reduce metronidazole → nitroso radicals → DNA strand breakage and synthesis inhibition in anaerobes/protozoa.

Absorption

Well absorbed orally; tₘₐₓ ~1–2 h; oral and IV exposures are comparable (dose-proportional).

Volume of distribution

~0.51–1.1 L/kg; penetrates CSF, saliva, breast milk; therapeutic concentrations in abscess pus.

Protein binding

<20% (low).

Metabolism

Hepatic oxidation (e.g., 2-hydroxymethyl metabolite) and glucuronidation; parent and hydroxyl-metabolite are microbiologically active.

Route of elimination

Primarily urinary (≈60–80% of dose as metabolites and ~20% unchanged); fecal ≈6–15%.

Half-life

~8 h (adults with normal organ function).

Clearance

Renal clearance ≈10 mL/min/1.73 m²; hemodialysis removes ~40–65% of a dose; exposure ↑ with hepatic impairment (dose reduction in Child-Pugh C).

Adverse Effects

Nausea, metallic taste, headache, dizziness; peripheral neuropathy with prolonged/high-dose use; dark urine; rare seizures/encephalopathy.

Toxicity

Overdose: supportive care; monitor neurologic status and hepatic function.

Pathways

Anaerobic nitroreduction → DNA damage; hepatic metabolic clearance; renal elimination of parent + conjugates.

Pharmacogenomic Effects/ADRs

No required PGx; variability in redox/activation pathways can influence susceptibility in pathogens rather than host.

3. Interactions

Drug Interactions

Warfarin/anticoagulants (↑ INR; monitor), busulfan (↑ exposure; avoid unless essential), enzyme modulators—cimetidine (↑ levels), phenytoin/phenobarbital (↓ levels), lithium (toxicity risk; monitor). Additive QT-prolongation risk with other QT-prolonging drugs reported in labeling.

Food Interactions

Food has minimal PK impact. Alcohol: avoid during therapy and for ≥3 days after last dose.

4. Categories

ATC Codes

J01XD01 (systemic imidazole antibacterial); A01AB17 (oral topical, stomatological); D06BX01 (dermatological, topical); G01AF01 (gynecological); P01AB01 (antiprotozoal, nitroimidazole)

Drug Categories

Antibacterial; Antiprotozoal; Nitroimidazole; Small molecule

Chemical Taxonomy

5-Nitroimidazole core with 2-hydroxyethyl side chain; weakly basic heteroaromatic nitro compound

Affected organisms

Humans (therapeutic use); targets anaerobic bacteria and select protozoa

5. Chemical Identifiers

UNII

140QMO216E

CAS number

443-48-1

InChI Key

VAOCPAMSLUNLGC-UHFFFAOYSA-N

InChI

InChI=1S/C6H9N3O3/c1-5-7-4-6(9(11)12)8(5)2-3-10/h4,10H,2-3H2,1H3

IUPAC Name

2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol

SMILES

OCCn1c(C)ncc1N+[O-]

6. References

PubChem Compound Summary: Metronidazole — formula C₆H₉N₃O₃, MW ~171.15, identifiers (CAS, InChI/Key, SMILES). pubchem.ncbi.nlm.nih.gov
FDA GSRS/UNII — UNII 140QMO216E, InChIKey VAOCPAMSLUNLGC-UHFFFAOYSA-N. precision.fda.gov
DailyMed/FDA labeling — absorption (well absorbed; tₘₐₓ 1–2 h), protein binding <20%, distribution to CSF/saliva/milk, urinary excretion 60–80% (≈20% unchanged), half-life ~8 h, renal clearance ~10 mL/min/1.73 m², hemodialysis removes 40–65%, hepatic-impairment dose guidance, mechanism text. DailyMed+1
Clinical PK reviews — Vd ~0.51–1.1 L/kg; low protein binding. PubMed+1
KEGG DRUG — ATC set J01XD01, A01AB17, D06BX01, G01AF01, P01AB01; formula and mass. KEGG
AccessData FDA labels and product labeling excerpts — distribution note, mechanism phrasing, interaction cautions (busulfan, QT risk, enzyme modulators). FDA Access Data+2Pfizer Labeling+2

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