Metronidazole Components
Chemical Structure and Active Ingredient
Metronidazole is a synthetic nitroimidazole compound with the chemical formula C6H9N3O3 (molecular weight 171.16), specifically 1-(β-hydroxyethyl)-2-methyl-5-nitroimidazole. 1
The drug belongs to the nitroimidazole class of antimicrobials, characterized by a 5-nitroimidazole ring structure that is essential for its biological activity. 2, 3
Inactive Ingredients in Tablet Formulations
The 250 mg and 500 mg oral tablets contain the following inactive components: 1
- Colloidal silicon dioxide - used as a glidant and anti-caking agent
- Hydroxypropyl cellulose - serves as a binder and disintegrant
- Lactose (anhydrous) - functions as a filler/diluent
- Microcrystalline cellulose - acts as a binder and disintegrant
- Sodium starch glycolate - provides rapid tablet disintegration
- Stearic acid - serves as a lubricant during tablet manufacturing
Mechanism of Action Related to Structure
The nitroimidazole structure undergoes reduction within anaerobic organisms and protozoa, generating toxic metabolites that cause DNA strand breakage, which explains its selective bactericidal and antiprotozoal activity. 2, 3 This nitro group reduction is critical to both the therapeutic effects and the biological properties of the drug. 4
Metabolites as Components
When administered, metronidazole is extensively metabolized by the liver into 5 metabolites, with the hydroxy metabolite being the most clinically significant component, possessing 30-65% of the parent compound's biological activity and a longer elimination half-life. 3, 5 This metabolite contributes substantially to the overall therapeutic effect and should be considered part of the active pharmaceutical system.
Human intestinal flora can also produce additional metabolites including acetamide and N-(2-hydroxyethyl)-oxamic acid through nitro group reduction. 4