Ciprofloxacin (Ciloxan)
Is It Right for You?
A complete guide to Ciprofloxacin (Ciloxan) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Ciprofloxacin?
Ciprofloxacin is a broad-spectrum fluoroquinolone antibiotic that has been in clinical use since the late 1980s. It is one of the most potent and widely prescribed antibiotics in the world, valued for its exceptional activity against a wide range of Gram-negative bacteria, good tissue penetration, and availability in both oral and intravenous forms -- with oral bioavailability approaching that of intravenous dosing, making it one of the few antibiotics that can step down from IV to oral without a significant loss in efficacy.
Ciprofloxacin belongs to the fluoroquinolone class of antibiotics, which work through a fundamentally different mechanism to penicillins, cephalosporins, and macrolides, making them effective against many organisms that have developed resistance to those drug classes.
In the UK, ciprofloxacin is used for a range of serious bacterial infections including complicated urinary tract infections, respiratory tract infections, gastrointestinal infections, bone and joint infections, and as prophylaxis in specific high-risk situations. It is also available as eye drops under the brand name Ciloxan for the treatment of bacterial conjunctivitis and corneal ulcers.
Due to concerns about fluoroquinolone-associated adverse effects -- particularly the risk of tendon damage, peripheral neuropathy, and aortic aneurysm -- regulatory guidance has increasingly restricted their use to situations where other antibiotics are not appropriate or have failed. Ciprofloxacin is now considered a reserve antibiotic for many indications in the UK and should not be used as a first-line treatment where safer alternatives exist.
Ciprofloxacin is available as tablets, oral suspension, intravenous infusion, and eye drops. It is available generically and under brand names including Ciproxin (oral/IV) and Ciloxan (eye drops).
Ciprofloxacin is a prescription-only medication in the UK. A licensed clinician must carefully assess your symptoms, medical history, and the appropriateness of a fluoroquinolone before prescribing -- which can now be done conveniently through a telehealth consultation.
What Conditions Is Ciprofloxacin Used For?
Ciprofloxacin is used for a range of bacterial infections, with prescribing now guided by the principle that it should only be used when other antibiotics are not appropriate:
traveller's diarrhoea caused by Campylobacter, Salmonella, Shigella, or enterotoxigenic E. coli; ciprofloxacin resistance in Campylobacter is now very high in the UK, limiting its usefulness for this indication.
ciprofloxacin's excellent bone penetration makes it valuable for chronic osteomyelitis and bone infections caused by susceptible Gram-negative organisms.
particularly those caused by Gram-negative organisms or where other antibiotics are not suitable.
typically used in combination with metronidazole to cover both Gram-negative and anaerobic bacteria.
ciprofloxacin is a primary treatment for cutaneous, inhalational, and gastrointestinal anthrax (Bacillus anthracis)
Ciloxan eye drops are used topically for bacterial eye infections, particularly those caused by Gram-negative organisms; minimal systemic absorption from topical use.
Regulatory bodies including the MHRA and the European Medicines Agency have issued guidance restricting the use of fluoroquinolone antibiotics including ciprofloxacin due to the risk of serious, disabling, and potentially irreversible adverse effects. Ciprofloxacin should only be used when clinically necessary and when other antibiotics are not appropriate. It must not be used as a first-line treatment for mild or self-limiting infections. Your clinician will carefully consider whether ciprofloxacin is the right choice for your specific infection.
How Does Ciprofloxacin Work?
Ciprofloxacin belongs to the fluoroquinolone class of antibiotics and works through a mechanism of action that is entirely distinct from all other major antibiotic classes -- making it effective against many organisms that are resistant to penicillins, cephalosporins, and macrolides.
Ciprofloxacin targets two essential bacterial enzymes involved in DNA replication and repair: DNA gyrase (topoisomerase II) and topoisomerase IV. These enzymes are responsible for managing the topology of bacterial DNA -- controlling the supercoiling, unwinding, and re-joining of DNA strands during replication, transcription, and repair. Without functional DNA gyrase and topoisomerase IV, bacteria cannot replicate their DNA, transcribe genes, or repair DNA damage.
Ciprofloxacin forms a stable complex with these enzymes and the DNA strand, effectively trapping them in a broken state. This causes irreparable double-stranded DNA breaks to accumulate within the bacterium, triggering the bacterial SOS response and ultimately leading to rapid cell death. This is a bactericidal mechanism -- ciprofloxacin actively kills bacteria rather than merely inhibiting their growth.
Ciprofloxacin has preferential activity against DNA gyrase in Gram-negative bacteria (making it particularly potent against organisms such as E. coli, Pseudomonas aeruginosa, and Haemophilus influenzae) and against topoisomerase IV in Gram-positive bacteria (though its activity against Gram-positives, particularly Streptococcus pneumoniae, is relatively weak compared to newer fluoroquinolones such as levofloxacin and moxifloxacin).
Ciprofloxacin is particularly valued for its excellent tissue and intracellular penetration -- it achieves high concentrations in the lungs, prostate, bone, bile, and urinary tract, making it effective for infections in these sites. Its oral bioavailability is approximately 70--80%, comparable to intravenous administration, which is unusually high for an antibiotic and allows effective oral treatment of infections that would otherwise require hospitalisation and IV therapy.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Ciprofloxacin can be taken with or without food. Food does not significantly affect its overall absorption, though it may slightly delay the time to peak concentration. Taking it with food may help reduce gastrointestinal side effects such as nausea.
Do not take ciprofloxacin with dairy products, calcium-fortified juices, or antacids containing aluminium, magnesium, or calcium -- and avoid iron and zinc supplements -- within 2 hours of taking ciprofloxacin. These products form insoluble complexes (chelation) with ciprofloxacin in the gut, drastically reducing its absorption by up to 90%. Ciprofloxacin should be taken at least 2 hours before or 6 hours after these products.
Take with a full glass of water and maintain adequate hydration throughout treatment. Ciprofloxacin can crystallise in the urine (crystalluria) if fluid intake is insufficient, potentially causing kidney damage.
Avoid excessive sunlight and UV exposure during treatment. Ciprofloxacin can cause photosensitivity, increasing the risk of sunburn and skin reactions. Use sunscreen and protective clothing when outdoors.
Stop ciprofloxacin immediately and contact your clinician if you develop any tendon pain, swelling, or weakness -- particularly in the Achilles tendon -- or any symptoms of peripheral neuropathy (numbness, tingling, or pain in the hands or feet). Do not wait to see if symptoms improve before seeking advice.
Complete the full prescribed course even if symptoms improve rapidly, to prevent relapse and the development of resistance.
Side Effects of Ciprofloxacin
Ciprofloxacin has a well-recognised profile of serious adverse effects that has led to increased regulatory scrutiny and restrictions on its use. While many patients tolerate it well for short courses, the risk of serious, disabling, and potentially irreversible adverse effects is greater than with most other antibiotic classes.
- Nausea (most common)
- Diarrhoea
- Abdominal discomfort
- Vomiting
- Headache
- Dizziness
- Rash
- Elevated liver enzymes (usually asymptomatic)
- Photosensitivity (increased sensitivity to sunlight)
- Tendinopathy and tendon rupture -- one of the most serious and well-recognised fluoroquinolone adverse effects; affects primarily the Achilles tendon but can affect any tendon; can occur during treatment or up to several months after stopping; risk is highest in elderly patients, those taking corticosteroids, and those with renal impairment; Achilles tendon rupture may require surgical repair
- Peripheral neuropathy -- numbness, tingling, burning, or weakness in the hands or feet; can be severe and may be irreversible; can occur at any point during treatment
- Central nervous system effects -- dizziness, confusion, agitation, tremor, hallucinations, seizures; ciprofloxacin can lower the seizure threshold
- QT interval prolongation and cardiac arrhythmias -- risk is greatest in patients with pre-existing cardiac conditions, electrolyte abnormalities, or those taking other QT-prolonging drugs
- Aortic aneurysm and aortic dissection -- fluoroquinolones are associated with an increased risk of serious aortic events; patients with known or suspected aortic disease should not receive ciprofloxacin
- C. difficile-associated diarrhoea -- ciprofloxacin is a high-risk antibiotic for C. difficile colitis; persistent watery or bloody diarrhoea requires immediate medical attention
- Severe allergic reaction (anaphylaxis) -- urticaria, facial swelling, difficulty breathing; requires immediate emergency treatment
- Severe skin reactions -- Stevens-Johnson Syndrome, Toxic Epidermal Necrolysis; very rare but potentially life-threatening
- Hepatotoxicity -- severe liver damage including fulminant hepatic failure; rare but reported
- Blood glucose disturbances -- both hypoglycaemia and hyperglycaemia; of particular relevance in diabetic patients
A small but significant number of patients experience a syndrome of multiple, concurrent, and potentially disabling adverse effects following fluoroquinolone treatment -- sometimes referred to as fluoroquinolone-associated disability (FQAD). This can include combinations of tendinopathy, peripheral neuropathy, CNS effects, musculoskeletal pain, and fatigue, which may persist for months or years after stopping the antibiotic. The MHRA has issued specific guidance warning prescribers and patients about this risk. If you develop new or worsening symptoms during or after ciprofloxacin treatment, stop the medication and contact your clinician promptly.
Drug Interactions
Ciprofloxacin has a number of clinically important drug interactions. Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting ciprofloxacin.
Ciprofloxacin prolongs the QT interval, and combining it with other QT-prolonging drugs significantly increases the risk of serious cardiac arrhythmias including Torsades de Pointes. This combination should generally be avoided. A full medication review is essential before prescribing.
Ciprofloxacin is a potent inhibitor of CYP1A2 and dramatically increases tizanidine blood levels -- by up to 10-fold -- causing severe hypotension, sedation, and potentially life-threatening toxicity. This combination is absolutely contraindicated.
Ciprofloxacin can enhance the anticoagulant effect of warfarin through CYP1A2 inhibition and effects on gut flora. INR should be monitored closely during and after treatment.
Concurrent use of ciprofloxacin with NSAIDs increases the risk of CNS stimulation and seizures. This combination should be used with caution, particularly in patients with a history of seizures.
Important Warnings
Fluoroquinolones including ciprofloxacin are associated with a risk of tendinitis and tendon rupture, most commonly affecting the Achilles tendon. This can occur during treatment or up to several months after completing a course. Risk is highest in patients aged over 60, those taking corticosteroids, and those with renal impairment or a history of tendon problems. Stop ciprofloxacin immediately and contact your clinician if you experience any tendon pain, swelling, or stiffness during or after treatment. Avoid strenuous physical activity until tendon injury is excluded.
Ciprofloxacin can cause CNS adverse effects including dizziness, confusion, agitation, tremor, hallucinations, and seizures. It lowers the seizure threshold and should be used with extreme caution in patients with a history of epilepsy or CNS disorders. Any neurological or psychiatric symptoms during treatment require immediate cessation and medical review.
Ciprofloxacin is one of the antibiotics most strongly associated with Clostridioides difficile colitis - a potentially life-threatening complication. Persistent diarrhoea during or after treatment must be assessed promptly. Anti-diarrhoeal medications should not be used without medical guidance in this context.
Ciprofloxacin is generally not recommended during pregnancy. Animal studies have shown arthropathy (joint damage) in immature animals, and while this has not been definitively demonstrated in humans, alternative antibiotics are preferred during pregnancy. It is excreted in breast milk in concentrations that may affect the infant. Breastfeeding is generally not recommended during ciprofloxacin treatment. Always discuss the risks and benefits with your clinician.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Ciprofloxacin FAQs
Yes. A licensed clinician can assess your symptoms, medical history, and the appropriateness of a fluoroquinolone antibiotic via a telehealth consultation. Given the MHRA guidance on fluoroquinolone risks, your clinician will carefully consider whether ciprofloxacin is the most appropriate choice for your infection and whether other antibiotics should be tried first. Prescriptions are typically sent to your preferred pharmacy the same day.
Ciprofloxacin has excellent oral bioavailability and achieves therapeutic blood levels rapidly, within 1-2 hours of the first dose. Most patients with urinary tract infections notice improvement in symptoms within 24--48 hours. For more complex infections - such as bone infections or pyelonephritis -- improvement may take several days. Always complete the full course regardless of how quickly symptoms resolve.
Regulatory bodies including the MHRA have increasingly restricted fluoroquinolone use due to the risk of serious, disabling, and potentially irreversible adverse effects - including tendon rupture, peripheral neuropathy, CNS effects, and aortic aneurysm. These risks are considered disproportionate for mild or self-limiting infections where safer alternatives exist. Ciprofloxacin should be reserved for infections where other antibiotics are not appropriate, have failed, or where its specific activity (particularly against Gram-negative organisms) is needed.
Stop taking ciprofloxacin immediately and contact your clinician. Tendon pain, swelling, or stiffness during ciprofloxacin treatment is a warning sign of fluoroquinolone-induced tendinopathy. Continuing treatment after tendon symptoms appear significantly increases the risk of tendon rupture, which may require surgical intervention. Rest the affected tendon, avoid strenuous exercise, and seek urgent medical review.
No - this is an important interaction. Dairy products, calcium-fortified juices, antacids, and iron or zinc supplements chelate with ciprofloxacin in the gut, forming insoluble complexes that cannot be absorbed. This can reduce ciprofloxacin absorption by up to 90%, rendering it potentially ineffective. Ciprofloxacin must be taken at least 2 hours before or 6 hours after any of these products, and should always be taken with plain water.
There is no direct dangerous pharmacological interaction between ciprofloxacin and alcohol. However, alcohol can worsen some of ciprofloxacin's CNS side effects such as dizziness and can impair immune function, potentially slowing recovery. Moderate alcohol consumption is not strictly prohibited, but heavy drinking during antibiotic treatment is inadvisable.
Ciloxan eye drops contain the same active ingredient -- ciprofloxacin -- but are formulated for topical application to the eye. When used as eye drops, systemic absorption is minimal, meaning the serious systemic side effects associated with oral ciprofloxacin (tendon damage, peripheral neuropathy, QT prolongation) are not a significant concern. Ciloxan is used specifically for bacterial conjunctivitis and corneal ulcers, where it delivers high concentrations directly to the site of infection.
A small but significant number of patients experience a debilitating syndrome of multiple concurrent adverse effects following fluoroquinolone treatment, sometimes called fluoroquinolone-associated disability or FQAD. This can include persistent tendon pain, peripheral neuropathy, joint pain, muscle weakness, cognitive difficulties, fatigue, and psychiatric symptoms - which may persist for months or years after stopping the antibiotic. The MHRA has recognised this syndrome and issued guidance to healthcare professionals and patients. If you experience multiple new symptoms during or after ciprofloxacin treatment, stop the medication and seek medical review promptly.