How Does Zidoval Gel Work in the Body
Chemical Composition, Mechanism of Action & Metabolic Effects Explained
Key Takeaways: How Zidoval Gel Works
- Active Ingredient: Metronidazole 7.5 mg/g, a nitroimidazole antibiotic.
- Primary Action: Disrupts bacterial DNA by forming toxic metabolites inside anaerobic bacteria.
- Target Condition: Bacterial vaginosis (BV) caused by anaerobic overgrowth.
- Treatment Course: One 5g applicator at bedtime for 5 consecutive days.
- Local Action: Works directly in the vagina; minimal systemic absorption but possible interactions.
- Avoid Alcohol: May cause disulfiram-like reaction (nausea, flushing, rapid heartbeat).
Zidoval gel is a vaginal gel containing metronidazole, an antibiotic that specifically targets the anaerobic bacteria responsible for bacterial vaginosis. By applying the gel directly to the site of infection, metronidazole penetrates bacterial cells and unleashes a cascade of chemical reactions that ultimately eradicate the infection while restoring the natural vaginal flora.
Important Medical Advice
If you experience severe allergic reactions (rash, itching, swelling), persistent vomiting, or neurological symptoms like confusion or numbness, stop using Zidoval gel and seek immediate medical attention. Avoid alcohol during treatment and for 48 hours after the last dose to prevent severe reactions.
Chemical Composition & Molecular Structure
Zidoval gel's active substance is metronidazole, a synthetic nitroimidazole derivative. Its chemical structure enables selective activation in anaerobic environments.
Metronidazole Properties
2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol
The nitro group at position 5 is critical for antibacterial activity—it gets reduced only in anaerobic bacteria.
C6H9N3O3
Contains carbon, hydrogen, nitrogen, and oxygen atoms arranged in an imidazole ring with a nitro substituent.
171.15 g/mol
Low molecular weight facilitates diffusion through bacterial cell membranes.
Excipients in Zidoval Gel
| Ingredient | Function | Relevant Information |
|---|---|---|
| Carbopol 974P | Gelling agent | Provides viscosity for vaginal retention |
| Disodium edetate | Stabiliser | Chelates metal ions to prevent degradation |
| Methyl parahydroxybenzoate (E218) | Preservative | May cause allergic reactions in sensitive individuals |
| Propyl parahydroxybenzoate (E216) | Preservative | Paraben, potential allergen |
| Propylene glycol (E1520) | Humectant | 30 mg per gram; may cause skin irritation |
| Sodium hydroxide | pH adjuster | Maintains gel at vaginal-compatible pH |
🗒️ Pharmaceutical Insight: The combination of parabens and propylene glycol ensures product stability and comfort, but individuals with known allergies should consult their pharmacist before use.
Mechanism of Action: How Metronidazole Kills Bacteria
Metronidazole is a prodrug that becomes active only under anaerobic conditions—exactly the environment found in bacterial vaginosis.
- Entry into bacteria: Metronidazole diffuses passively through the cell membranes of anaerobic bacteria and protozoa.
- Reduction by bacterial enzymes: Inside the cell, the nitro group is reduced by ferredoxin or flavodoxin (nitroreductases) that are unique to anaerobic organisms. This creates short-lived cytotoxic compounds.
- DNA damage: These reduced metabolites interact with bacterial DNA, causing strand breakage, helix destabilisation, and inhibition of nucleic acid synthesis.
- Cell death: The cumulative damage halts bacterial replication and leads to rapid cell death.
Why It's Selective for Anaerobes
Aerobic bacteria lack the necessary electron transport proteins to reduce metronidazole, so the drug remains inactive and harmless to them. This selectivity preserves beneficial lactobacilli in the vagina while eradicating anaerobes like Gardnerella vaginalis, Prevotella spp., and Mobiluncus.
🗒️ Microbiological Insight: The reduction of metronidazole creates nitroso radicals that are highly reactive. They covalently bind to DNA, leading to rapid bacterial death—often within hours of exposure.
Metabolic Pathway & Excretion
Although applied vaginally, a fraction of metronidazole is absorbed into the bloodstream and undergoes hepatic metabolism.
Absorption and Distribution
Following vaginal application of Zidoval gel, peak plasma concentrations are about 2% of those seen after oral metronidazole (approx. 0.2–0.4 µg/mL). Systemic absorption is low but clinically relevant for drug interactions and alcohol avoidance.
Metabolism
- Liver: Metronidazole is oxidised by hepatic CYP450 enzymes (mainly CYP2A6 and CYP3A4) to form two major metabolites: hydroxy-metronidazole (active) and an acid metabolite (inactive).
- Half-life: 6–8 hours for metronidazole; metabolites may persist longer.
Excretion
- Renal: 60–80% of the dose is excreted in urine (as unchanged drug and metabolites), imparting a dark brownish colour—this is harmless.
- Faecal: Minor elimination via bile.
- Vaginal: Unabsorbed gel is discharged naturally.
🗒️ Clinical Correlation: Because of slight systemic absorption, avoid alcohol during treatment and for 48 hours after finishing—metronidazole inhibits acetaldehyde dehydrogenase, leading to disulfiram-like reactions.
Clinical Efficacy in Bacterial Vaginosis
Zidoval gel is indicated for the treatment of bacterial vaginosis in adult women. Clinical trials demonstrate high cure rates with the standard 5-day regimen.
Typical Treatment Outcomes
| Parameter | Result |
|---|---|
| Clinical cure rate (days 21–30) | 75–85% |
| Reduction in clue cells | Significant by day 7 |
| Restoration of normal vaginal pH | Typically within 1 week |
| Recurrence rate within 3 months | ~20% (similar to other BV therapies) |
Why Full Course Matters
As noted in the PIL, you must complete all five doses even if symptoms improve early. Incomplete treatment can lead to regrowth of resistant bacteria and recurrence.
Safety Profile & Side Effects
Zidoval gel is generally well tolerated, but like all medicines, it can cause side effects. Below are those reported in clinical studies and the PIL.
Common Side Effects (≥1/100 to <1/10)
- Headache, dizziness
- Nausea, vomiting, stomach cramps
- Unpleasant or metallic taste
- Vaginal thrush (candidiasis), discharge, pelvic discomfort
- Skin reactions: dryness, redness, itching, burning
- Decreased appetite, depression
Uncommon Side Effects (≥1/1000 to <1/100)
- Fatigue, irritability, insomnia
- Paraesthesia (tingling in fingers/toes)
- Diarrhoea, constipation, bloating, dry mouth
- Muscle cramps, darkened urine
- Urinary tract infection symptoms, vulval swelling
- Menstrual changes (spotting, painful periods)
Rare / Frequency Not Known
- Severe allergic reactions (urticaria, angioedema)
- Neurological: encephalopathy, optic neuropathy (with prolonged high-dose oral use—very unlikely with vaginal gel)
🗒️ Safety Note: If you develop vaginal thrush symptoms during treatment, consult your doctor—you may need an antifungal alongside or after Zidoval.
Zidoval Gel Mechanism FAQs
How does Zidoval gel stay active inside the vagina?
The gel contains Carbopol, which bioadheres to vaginal mucosa, releasing metronidazole gradually overnight. This ensures prolonged contact with bacteria.
Why must I avoid alcohol with Zidoval gel?
Metronidazole blocks the enzyme that breaks down alcohol, leading to a build-up of acetaldehyde. This causes flushing, nausea, vomiting, and rapid heartbeat.
Can Zidoval gel affect my partner during intercourse?
It's recommended to avoid intercourse during treatment. If you do, your partner may experience mild penile irritation; the gel can also weaken condoms (latex).
What happens if I miss a dose?
Apply the missed dose as soon as you remember, but if it's almost time for the next dose, skip it. Do not double the dose.
How long does Zidoval gel take to clear BV symptoms?
Most women notice improvement within 2–3 days, but you must complete the full 5-day course to prevent recurrence.
Need Treatment for Bacterial Vaginosis?
If you're experiencing symptoms like unusual discharge or odour, Zidoval gel may be an appropriate treatment after a doctor's assessment.
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Medical Content Manager
Nabeel is a co-founder, and medical content manager of Chemist Doctor. He works closely with our medical team to ensure the information is accurate and up-to-date.
Medical Doctor
Dr. Feroz is a GMC-registered doctor and a medical reviewer at Chemist Doctor. He oversees acute condition and urgent care guidance.
Medical Director
Usman is a co-founder, and medical director of Chemist Doctor. He leads the organisation's strategic vision, bridging clinical and operational priorities.
Review Date: 25 February 2026
Next Review: 25 August 2026
Published on: 25 February 2026
Last Updated: 25 February 2026