Norfloxacin 400 mg: Uses, Dosage, Side Effects and Why It Left US Pharmacies

Norfloxacin 400 mg is an older fluoroquinolone antibiotic, in the same family as ciprofloxacin and levofloxacin. It was sold in the US as Noroxin for urinary tract infections, gonorrhea and prostatitis, and it is still sold in India and other countries under brands such as Norflox. If you have been prescribed it, or you are pricing it online, there are three things worth knowing: what it was approved for and at what dose, why regulators now want it kept for cases with no alternative, and why US pharmacies no longer stock it.

This guide uses the last US prescribing information for Noroxin (revised July 2016), the FDA's own notices on its withdrawal, the European Medicines Agency's 2018 review of the whole drug class, and clinical trials. We sell Norflox 400 and Norflox 200, so we have an interest here; where the evidence argues against using norfloxacin, we say so.

The short answer

Norfloxacin 400 mg is taken twice a day: for 3 days for simple cystitis caused by the common bacteria, 7 to 10 days for other uncomplicated urinary infections, 10 to 21 days for complicated ones and 28 days for prostatitis. In trials the most common side effects were nausea (4.2%) and headache (2.8%), but like every fluoroquinolone it carries a boxed warning for rare, disabling and possibly permanent effects on tendons, nerves and the brain, and the 2016 US label says to keep it for uncomplicated urinary infections only when there is no other option. Merck stopped selling Noroxin in the US in 2015, the FDA withdrew its approval in November 2016, and in 2017 the FDA confirmed that the withdrawal was not for safety or effectiveness reasons. Today norfloxacin is not sold in the US or the UK. Its best evidence outside urinary infections is in preventing a dangerous abdominal infection in people with advanced cirrhosis, which is a specialist use.

What norfloxacin is

Norfloxacin is a synthetic fluoroquinolone antibiotic. It kills bacteria by blocking enzymes they need to copy their DNA. Only part of an oral dose is absorbed (at least 30% to 40% in fasting volunteers), and about a quarter to a third of a dose is recovered unchanged in the urine within 24 hours. The label's approved uses were all infections of the urinary and genital tract. Its effective half-life in blood is 3 to 4 hours, and the label doses it every 12 hours.

Brands include:

• Noroxin (Merck), the original US brand, approved by the FDA on 31 October 1986 and now discontinued.
• Norflox (Cipla), sold in India as Norflox 400 and Norflox 200, among other generic brands.

The FDA's drug approvals database lists only two norfloxacin products, Noroxin tablets and Chibroxin eye drops, both discontinued. There is no current FDA-approved norfloxacin tablet, and the FDA's NDC directory has no listing for one.

What the US label approved it for

The 2016 Noroxin label listed these adult uses, caused by susceptible bacteria:

• Uncomplicated urinary tract infections, including cystitis, but only in patients with no other treatment options.
• Complicated urinary tract infections.
• Uncomplicated gonorrhea of the urethra or cervix.
• Prostatitis caused by E. coli.

The label also says a urine culture and sensitivity test should be done, and treatment changed if the results show the bacteria are resistant. That step matters more now than in 1986: by 2007, for example, resistance in gonorrhea had spread so far that US guidance dropped the whole class for it (see below).

Norfloxacin 400 mg dosage

Infection	Dose	How often	How long
Uncomplicated cystitis due to E. coli, K. pneumoniae or P. mirabilis	400 mg	Every 12 hours	3 days
Uncomplicated UTI due to other listed bacteria	400 mg	Every 12 hours	7 to 10 days
Complicated UTI	400 mg	Every 12 hours	10 to 21 days
Uncomplicated gonorrhea (label dose, no longer recommended)	800 mg	Single dose	1 day
Acute or chronic prostatitis	400 mg	Every 12 hours	28 days

The total daily dose in every case is 800 mg, and the label says not to exceed it. Norflox 200 is half the label's unit dose; two 200 mg tablets make one 400 mg dose.

How to take it

• Take it at least 1 hour before or at least 2 hours after a meal, milk or other dairy products.
• Take it with a glass of water and drink enough fluid during the course. Crystals in the urine were seen in some volunteers given up to twice the daily dose (and in some given placebo); as a precaution the label says to drink enough fluid and not exceed the daily dose.
• Do not take multivitamins, iron, zinc, antacids containing magnesium or aluminium, or sucralfate within 2 hours of a dose. They reduce absorption.
• Finish the prescribed course unless a doctor tells you to stop, or you develop one of the serious reactions below.

Doses for kidney problems and older adults

With a creatinine clearance of 30 mL/min/1.73 m² or less, the label dose is one 400 mg tablet once a day for the same duration. Older adults with clearance above that level take the normal dose. The label notes that urine levels stay above what is needed for most susceptible urinary bacteria even at very low kidney function.

Common side effects

In the label's multiple-dose studies of 2,032 people, 3.6% had side effects judged to be caused by the drug. The events above 1% were nausea, headache, dizziness and weakness. Less common were abdominal pain, diarrhoea, dry mouth, heartburn, rash, itching and sleepiness. Some laboratory values changed in a small share of people, such as raised eosinophils, raised liver enzymes and a lower white cell count (each about 1% to 1.5%). After marketing, the most often reported reaction was rash.

The boxed warning: rare but serious

The 2016 label carries the boxed warning shared by every fluoroquinolone in the US. It says these drugs have been linked to disabling and potentially irreversible serious reactions that have occurred together:

• Tendinitis and tendon rupture, most often the Achilles tendon, which can start within hours or days, or months after the course ends. The risk is higher over 60, with corticosteroids, and after kidney, heart or lung transplants.
• Peripheral neuropathy: pain, burning, tingling, numbness or weakness, which may be permanent.
• Central nervous system effects, including seizures, raised pressure in the skull, confusion, tremor and psychosis.

The box also warns that fluoroquinolones can worsen muscle weakness in myasthenia gravis, which has led to deaths and the need for breathing support. Avoid norfloxacin with this condition.

Because of these risks, the label says to reserve norfloxacin for uncomplicated urinary infections in people with no alternative, noting that for some patients these infections clear up on their own. Stop the drug and contact a doctor at the first sign of tendon pain, nerve symptoms, rash or jaundice.

Other warnings and precautions in the label

• Allergic reactions, some after the first dose, can be severe. Stop at the first sign of a rash.
• Heart rhythm: norfloxacin can prolong the QT interval. Avoid it with class IA or class III antiarrhythmics such as quinidine, procainamide, amiodarone or sotalol, and use caution with other drugs that prolong QT and with low potassium.
• Sun sensitivity: exaggerated sunburn can occur; avoid strong sun and sunbeds.
• C. difficile diarrhoea can occur during or after any antibiotic course.
• Seizure risk: use with caution in epilepsy and other conditions that make seizures more likely.

Who should not take norfloxacin

• Anyone who has had an allergic reaction, tendinitis or tendon rupture with norfloxacin or any other quinolone. This is the label's contraindication.
• People with myasthenia gravis, a history of tendon disorders, or previous peripheral neuropathy, in whom the label says to avoid it.
• Children and teenagers under 18, pregnant women and breastfeeding mothers: the label says safety and effectiveness have not been established, and quinolones damaged joint cartilage in young animals.

Drug interactions

• Theophylline: levels can rise; monitoring is advised.
• Warfarin and similar blood thinners: the anticoagulant effect can increase; check clotting tests.
• Cyclosporine: levels can rise; monitor.
• Glyburide: rare severe low blood sugar; check glucose.
• Drugs cleared by the CYP1A2 enzyme, such as caffeine, clozapine, ropinirole and tizanidine: levels may rise. Our tizanidine interactions guide explains why this matters for that drug.
• Nitrofurantoin: not recommended together, because it may block norfloxacin's effect in the urinary tract.
• Probenecid reduces how much norfloxacin reaches the urine.
• NSAID painkillers such as ibuprofen: taken with a quinolone, they may increase the risk of nervous system stimulation and seizures; use with caution.
• Antiarrhythmics: avoid class IA and class III drugs (see heart rhythm above).

How well does it work for cystitis?

The best head-to-head data for the 3-day course come from a randomised trial in about 950 women aged 18 to 65 with acute cystitis, comparing 3 days of norfloxacin 400 mg twice daily with 3 days of pivmecillinam 400 mg twice daily.

Outcome	Pivmecillinam	Norfloxacin
Bacteria cleared at early follow-up	222 of 298 (75%)	276 of 302 (91%)
Cured or improved by day 4	434 of 457 (95%)	425 of 442 (96%)
Clinical cure at day 11 (give or take 2 days)	360 of 437 (82%)	381 of 433 (88%)

Norfloxacin cleared the bacteria more often, but how the women felt was close between the two drugs. In 30% of each group, urine cultures before treatment were negative, a reminder that not every case of cystitis symptoms is a bacterial infection. Side effects were similar. This trial is from 2002, and resistance patterns have changed since; a urine culture is the way to know whether a fluoroquinolone will work for you now.

Why US pharmacies no longer stock it

The timeline comes from the FDA's own Federal Register notice:

• 31 October 1986: Noroxin approved for Merck.
• 13 October 2015: Merck tells the FDA it is discontinuing Noroxin.
• 4 October 2016: the FDA announces it is withdrawing approval of the Noroxin application, effective 3 November 2016.
• December 2017: after a petition from a generic company, the FDA determines that Noroxin was not withdrawn from sale for reasons of safety or effectiveness. That decision allows generic norfloxacin applications to be approved in future if they meet the other requirements.

As of October 2026 the FDA's databases show no approved norfloxacin tablet on sale. In practice, US doctors prescribe other antibiotics. A 2023 review in Hepatology Communications notes that norfloxacin is not available in the United Kingdom or the United States.

What Europe decided in 2018

In November 2018 the European Medicines Agency announced the results of a review of disabling, long-lasting side effects with quinolone and fluoroquinolone antibiotics, including norfloxacin. Four older quinolones (cinoxacin, flumequine, nalidixic acid and pipemidic acid) were to be suspended. For the remaining fluoroquinolones, the EMA said they should not be used:

• for infections that might get better without treatment or are not severe, such as throat infections;
• for non-bacterial infections, such as non-bacterial chronic prostatitis;
• to prevent travellers' diarrhoea or recurring lower urinary tract infections;
• for mild or moderate bacterial infections unless other antibiotics commonly recommended for them cannot be used.

Gonorrhea: a label use that no longer applies

The Noroxin label still listed a single 800 mg dose for uncomplicated gonorrhea. In 2007 the US Centers for Disease Control and Prevention stopped recommending fluoroquinolones for gonococcal infections, because fluoroquinolone resistance in gonorrhea had become widespread in the United States. Do not use norfloxacin to treat suspected gonorrhea; it needs testing and the current recommended treatment. The label also advises a syphilis blood test for anyone treated for gonorrhea.

Norfloxacin in cirrhosis: its strongest evidence today

People with cirrhosis and fluid in the abdomen (ascites) can develop spontaneous bacterial peritonitis, an infection of that fluid that is often fatal. Norfloxacin 400 mg a day, given long term, has been tested to prevent it.

Trial	Patients	Result
Ginés 1990 (prevention of recurrence)	80 patients who had recovered from peritonitis	Recurrence in 5 of 40 on norfloxacin vs 14 of 40 on placebo; 1-year probability 20% vs 68%
Fernández 2007 (prevention of a first episode)	68 high-risk patients with low-protein ascites	1-year probability of peritonitis 7% vs 61%; survival at 1 year 60% vs 48%
Moreau 2018 (largest placebo-controlled trial)	291 patients with Child-Pugh C cirrhosis, 6 months	6-month death rate 14.8% vs 19.7%, not a significant difference by the main analysis; fewer bacterial infections; a survival benefit appeared only in patients with low-protein ascites
Mücke 2020 (network meta-analysis)	1,626 patients in 12 trials	Norfloxacin still better than placebo, but its effect on peritonitis fell over time (8.2% per year from 1992 to 2015); it was not better than other antibiotics

This is not a self-treatment use. Who needs prevention, and with which antibiotic, is decided by a liver specialist, and in countries without norfloxacin other antibiotics are used.

Norfloxacin vs ciprofloxacin

Both are fluoroquinolones with the same class boxed warning. The practical difference today is availability: ciprofloxacin is still approved and sold in the US, while norfloxacin is not, so a US prescription for a fluoroquinolone will be for ciprofloxacin or levofloxacin rather than norfloxacin. For simple cystitis, regulators in both the US and Europe now prefer doctors to choose a non-fluoroquinolone first. Our nitrofurantoin guide covers one of the common alternatives, and its limits.

Resistance: why a culture matters

The label already recorded bacteria becoming resistant during norfloxacin treatment in less than 1% of patients treated. Resistance is the reason CDC dropped the class for gonorrhea, and the 2020 cirrhosis meta-analysis, written against a background of rising multidrug-resistant bacteria, found norfloxacin's preventive effect falling over time; its authors said the cause still needs study. If symptoms do not improve within a few days, or come back soon after, a urine culture shows whether the bacteria respond to norfloxacin or need a different drug. Our guide to antibiotic resistance explains why it matters beyond one infection.

When to get urgent help

• Sudden pain, swelling or a snap in a tendon, especially the back of the ankle. Rest the leg and stop the drug.
• Tingling, burning, numbness or weakness in the hands or feet.
• Swelling of the face or throat, trouble breathing, hives or a spreading rash.
• Seizures, hallucinations, severe confusion or new muscle weakness.
• Fainting or a fast, irregular heartbeat.
• Watery or bloody diarrhoea during or after the course.
• Fever, pain in the side or back, or vomiting with a urinary infection, which can be a sign of a kidney infection.

Prescription and legal status

Norfloxacin is a prescription antibiotic wherever it is sold. In the US there is no approved product, and the FDA's personal importation policy is narrow and not a permission to import unapproved medicines. Antibiotics should be taken only for an infection a clinician has diagnosed, at the dose and for the length of time prescribed.

Related guides

See our nitrofurantoin for UTI guide for a non-fluoroquinolone option, and our antibiotic resistance guide for why the choice of antibiotic matters.

Sources

• NOROXIN (norfloxacin) tablets, US prescribing information, Merck, revised July 2016. FDA label PDF
• US Food and Drug Administration. Determination That NOROXIN (Norfloxacin) Tablets, 400 Milligrams, Was Not Withdrawn From Sale for Reasons of Safety or Effectiveness. Federal Register, 12 December 2017. Federal Register
• US Food and Drug Administration, openFDA drug approvals and NDC directory, searched for norfloxacin on 14 October 2026.
• European Medicines Agency. Disabling and potentially permanent side effects lead to suspension or restrictions of quinolone and fluoroquinolone antibiotics. 16 November 2018. EMA
• Centers for Disease Control and Prevention. Update to CDC's sexually transmitted diseases treatment guidelines, 2006: fluoroquinolones no longer recommended for treatment of gonococcal infections. MMWR 2007. PMID 17431378.
• Nicolle LE et al. Three days of pivmecillinam or norfloxacin for treatment of acute uncomplicated urinary infection in women. Scandinavian Journal of Infectious Diseases 2002. PMID 12195873.
• Ginés P et al. Norfloxacin prevents spontaneous bacterial peritonitis recurrence in cirrhosis: results of a double-blind, placebo-controlled trial. Hepatology 1990. PMID 2210673.
• Fernández J et al. Primary prophylaxis of spontaneous bacterial peritonitis delays hepatorenal syndrome and improves survival in cirrhosis. Gastroenterology 2007. PMID 17854593.
• Moreau R et al. Effects of long-term norfloxacin therapy in patients with advanced cirrhosis. Gastroenterology 2018. PMID 30144431.
• Mücke MM et al. Efficacy of norfloxacin prophylaxis to prevent spontaneous bacterial peritonitis: a systematic review and meta-analysis. Clinical and Translational Gastroenterology 2020. PMID 32955202.
• Crocombe D, O'Brien A. Antimicrobial prophylaxis in decompensated cirrhosis: friend or foe? Hepatology Communications 2023. PMID 37655979.

This guide is for information only and is not medical advice. Norfloxacin is a prescription antibiotic. Do not start, stop or change an antibiotic course without a clinician's advice.