Antibiotic Cost & Duration Calculator
Calculate the total number of pills and estimated cost for common antibiotics based on your treatment needs.
Select your infection type and treatment duration to see which antibiotic might be most cost-effective for you.
Key Takeaways
- Flagyl ER (Metronidazole) is a longâacting nitroimidazole used for anaerobic infections.
- Tinidazole and Secnidazole provide similar coverage with onceâdaily dosing.
- Clindamycin is a good choice when resistance to nitroimidazoles is a concern.
- Amoxicillinâclavulanate and Doxycycline cover a broader range of bacteria but lack strong anaerobic activity.
- Cost, sideâeffect profile, and dosing convenience often decide the best alternative.
When your doctor mentions Flagyl ER, youâre looking at a onceâdaily, extendedârelease version of Metronidazole that promises steadier blood levels and fewer pills. But you might wonder whether another drug could work better for your infection, budget, or lifestyle. This guide breaks down the most common alternatives, compares them sideâbyâside, and helps you pick the right option for typical anaerobic infections such as bacterial vaginosis, trichomoniasis, or intraâabdominal abscesses.
What is Flagyl ER?
Flagyl ER is the brand name for the extendedârelease formulation of Metronidazole, a nitroimidazole antibiotic that targets anaerobic bacteria and certain protozoa. It was introduced in the UK market in 2018 and is typically prescribed as a 500mg tablet taken once daily for 7-10days, depending on the infection.
How Metronidazole Works
Metronidazole (the active ingredient in Flagyl ER) enters the bacterial cell and is reduced by anaerobic enzymes into reactive compounds. These compounds damage DNA and lead to cell death. Because the drug is activated only in lowâoxygen environments, it spares most human cells, making it highly effective against anaerobes like Bacteroides fragilis, Clostridium difficile, and protozoa such as Trichomonas vaginalis.
Typical Clinical Uses
Doctors prescribe Flagyl ER for:
- Pelvic inflammatory disease (PID)
- Bacterial vaginosis
- Trichomoniasis
- Complicated intraâabdominal infections
- Certain skin and softâtissue infections caused by anaerobes

Alternatives at a Glance
Four main drug families compete with Metronidazole for anaerobic coverage:
- Tinidazole - a nitroimidazole with a longer halfâlife, allowing onceâdaily dosing for 3â5days.
- Secnidazole - another nitroimidazole formulated for a singleâdose regimen in many infections.
- Clindamycin - a lincosamide antibiotic that covers anaerobes and some gramâpositive organisms, often used when resistance to nitroimidazoles is suspected.
- Amoxicillinâclavulanate - a betaâlactam combo that offers broadâspectrum coverage, including many anaerobes, but requires three daily doses.
- Doxycycline - a tetracycline with activity against certain anaerobes and a convenient onceâdaily schedule, though not a firstâline choice for deep anaerobic infections.
SideâEffect Profile Comparison
All antibiotics carry risks, but the patterns differ:
- Metronidazole (Flagyl ER) - metallic taste, nausea, possible peripheral neuropathy with prolonged use.
- Tinidazole - similar gastrointestinal upset, but fewer reports of metallic taste.
- Secnidazole - generally wellâtolerated; mild headache is the most common complaint.
- Clindamycin - higher incidence of antibioticâassociated diarrhea, including C.diff infection.
- Amoxicillinâclavulanate - risk of liver enzyme elevation and frequent diarrhea.
- Doxycycline - photosensitivity and esophageal irritation if not taken with water.
Direct Comparison Table
Drug | Formulation | Typical Dose | Key Indications | Average Cost (GBP) | Common Side Effects |
---|---|---|---|---|---|
Flagyl ER | Extendedârelease tablet | 500mg once daily | Anaerobic intraâabdominal, PID, BV | ÂŁ8â10 per pack (10 tablets) | Nausea, metallic taste, neuropathy (rare) |
Tinidazole | Immediateârelease tablet | 2g single dose or 500mg daily 3days | Trichomoniasis, giardiasis, bacterial vaginosis | ÂŁ12â15 per pack (5 tablets) | Headache, nausea, less metallic taste |
Secnidazole | Singleâdose capsule | 2g oneâtime dose | Trichomoniasis, bacterial vaginosis | ÂŁ20â22 per dose | Mild headache, occasional GI upset |
Clindamycin | Immediateârelease tablet | 300mg 4â6 times daily | Deep softâtissue infections, anaerobic abscesses | ÂŁ6â9 per pack (10 tablets) | Diarrhea, C.diff risk, rash |
Amoxicillinâclavulanate | Tablet | 875mg/125mg three times daily | Mixedâflora intraâabdominal, sinus, dental infections | ÂŁ4â7 per pack (21 tablets) | Diarrhea, liver enzyme rise |
Doxycycline | Capsule | 100mg twice daily | Chlamydia, acne, some anaerobic skin infections | ÂŁ5â8 per pack (21 capsules) | Photosensitivity, esophagitis |
Pros and Cons of Each Option
Flagyl ER offers the convenience of onceâdaily dosing and proven efficacy against a wide range of anaerobes, but it can cause a metallic taste that many patients find unpleasant.
Tinidazole shortens the treatment period to three days, which improves adherence. However, it is a bit pricier and not always covered by NHS formularies.
Secnidazole is the ultimate âoneâpillâ solution, ideal for busy patients. The tradeâoff is a higher perâdose cost and limited availability in some pharmacies.
Clindamycin shines when Metronidazole resistance is suspected, but the risk of C.diff colitis demands close monitoring.
Amoxicillinâclavulanate covers both aerobic and anaerobic bacteria, making it a good âbroadâspectrumâ backup, yet it requires three daily doses, which can be cumbersome.
Doxycycline provides a onceâdaily option if combined with another antibiotic, but its anaerobic activity is modest compared with nitroimidazoles.
Choosing the Right Drug for Your Situation
Consider these decision points:
- Infection type - Deep intraâabdominal abscesses usually need Flagyl ER or Clindamycin; uncomplicated bacterial vaginosis can be treated with Tinidazole or Secnidazole.
- Adherence concerns - If you struggle with multiple daily pills, Secnidazole (single dose) or Flagyl ER (once daily) are best.
- Cost constraints - Amoxicillinâclavulanate and generic Metronidazole are the cheapest, but you may need more tablets.
- Sideâeffect tolerance - Patients with a history of C.diff should avoid Clindamycin.
- Drug interactions - Metronidazole and Tinidazole both inhibit CYP2C9; avoid concurrent warfarin without monitoring.
Discuss these factors with your prescriber; they can tailor the regimen to your medical history and lifestyle.

Safety Tips and Common Interactions
All nitroimidazoles (Flagyl ER, Tinidazole, Secnidazole) share a key interaction: they turn alcohol into acetaldehyde, causing flushing, nausea, and rapid heartbeat. Avoid alcohol for 24hours after the last dose.
Clindamycin can trigger severe diarrhea; if you notice watery stools, call your doctor promptly.
Amoxicillinâclavulanate may raise liver enzymes; baseline liver function tests are advisable for patients with hepatitis.
Doxycycline increases sun sensitivity-use sunscreen and wear protective clothing.
Cost and Availability in the UK (2025)
Pricing shown in the table reflects typical NHS prescription charge exemptions and private pharmacy rates. Flagyl ER is widely stocked in both community pharmacies and online UK dispensaries. Tinidazole and Secnidazole, while approved, are less common and often ordered through specialty pharmacies.
When to Stick With Flagyl ER
If you have a confirmed anaerobic infection, no known drug allergies, and can tolerate the occasional metallic taste, Flagyl ER remains the firstâline choice in most UK guidelines. Its onceâdaily schedule reduces missed doses, and the extendedârelease formulation maintains steady drug levels, which is especially important for severe intraâabdominal infections.
Final Thoughts
Choosing an antibiotic isnât just about the cheapest pill; itâs about matching the drugâs strengths to your infection, your health profile, and your daily routine. Flagyl ER offers a reliable balance of efficacy and convenience, while Tinidazole, Secnidazole, Clindamycin, Amoxicillinâclavulanate, and Doxycycline each bring niche advantages. Talk to your clinician, weigh the sideâeffect profiles, and consider the costâtoâbenefit ratio before deciding.
Frequently Asked Questions
Can I switch from Flagyl ER to Tinidazole midway through treatment?
Switching is generally safe if youâve completed at least 48hours of Metronidazole, but you should inform your doctor. The two drugs share similar mechanisms, so overlapping therapy isnât needed, and dosage adjustments may be required.
Why does Flagyl ER cause a metallic taste?
The metallic flavor comes from the drugâs interaction with taste receptors in the mouth. Itâs a wellâdocumented side effect of nitroimidazoles and tends to lessen after the first few days.
Is Secnidazole approved for use in the UK?
Yes, Secnidazole received MHRA approval in 2022 for singleâdose treatment of bacterial vaginosis and trichomoniasis. Availability may be limited to specialist pharmacies.
Can I take Flagyl ER with alcohol?
No. Consuming alcohol while on Flagyl ER or any nitroimidazole can cause a severe reaction called disulfiramâlike effect, leading to flushing, nausea, and rapid heartbeat. Avoid alcohol for at least 24hours after the final dose.
Which alternative is best for patients with a history of C.diff?
Clindamycin carries a higher C.diff risk, so for such patients Flagyl ER, Tinidazole, or Secnidazole are safer choices, provided the infection is susceptible.
1 Comments
Adam O'Rourke
Oh sure, because popping a single pill is the ultimate cure đ