Fluoroquinolone antibacterials
ATC code: J01MA02 (Ciprofloxacin)
Inhibits bacterial DNA gyrase (topoisomerase II) and topoisomerase IV – blocking bacterial DNA replication and transcription. Active against gram-negative flora (E. coli, Pseudomonas, Klebsiella), some gram-positive organisms (Staphylococcus aureus), and atypicals. A moderate inhibitor of CYP1A2 and a weaker inhibitor of CYP3A4 – a source of clinically significant interactions. Chelation with divalent and trivalent cations (Mg2+, Ca2+, Fe2+, Al3+) markedly reduces absorption. black-box warnings in older adults: tendinitis, tendon rupture, aortic aneurysm, QT prolongation.
First line
First-line for complicated urinary tract infections and pyelonephritis in adults. Not recommended as first-line for uncomplicated cystitis – nitrofurantoin, fosfomycin, or TMP-SMX are preferred. warns of serious adverse effects and advises reserving fluoroquinolones for uncomplicated infections only when no alternatives exist.
First line
First-line for severe traveler's diarrhea with fever or bloody stools. Mild cases are managed with rehydration and loperamide. Short course of 1–3 days. Rising resistance in Southeast Asia limits efficacy; azithromycin is the alternative for that region.
Second line
Ciprofloxacin is not first-line for community-acquired pneumonia. It is used only when Pseudomonas aeruginosa is suspected – typically in patients with structural lung disease. For standard CAP, respiratory fluoroquinolones – levofloxacin or moxifloxacin – are preferred.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Ciprofloxacin is prescribed for upper respiratory infections, bronchitis and as a fallback for viral illnesses. 2024 AWaRe and ESCMID 2020 strictly confine fluoroquinolones to serious infections. The 2018 PRAC and Drug Safety Communication 2016 cited tendon damage, peripheral neuropathy and aortic aneurysm risk; an FDA boxed warning restricts use in uncomplicated UTIs and sinusitis to cases without alternatives.
Calcium forms insoluble chelate complexes with fluoroquinolones in the GI lumen; ciprofloxacin absorption drops 30–50%. Separate doses by at least 2 hours: fluoroquinolone 2 hours before or 6 hours after calcium.
Source: FDA: Cipro (ciprofloxacin) prescribing information (2021)
Dairy products contain calcium, which binds fluoroquinolones in the gut and reduces absorption by 30–50%. Do not take ciprofloxacin with milk, yogurt, or cheese – separate by at least 2 hours.
Source: FDA: Cipro (ciprofloxacin) prescribing information (2021)
28 pairs found. Sorted from critical to minor.
Mechanism
Additive QT prolongation. Amiodarone strongly blocks IKr potassium channels, ciprofloxacin weakly but dose-dependently. Ciprofloxacin also inhibits CYP1A2 (a minor amiodarone clearance route).
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Avoid where possible. Alternative antibiotic: a cephalosporin (no QT effect). If ciprofloxacin is needed, ECG before start and at day 3, with potassium and magnesium maintained.
Sources
Mechanism
Additive QT prolongation. Ciprofloxacin additionally blocks CYP1A2 – an amitriptyline metabolic route. Amitriptyline plasma levels rise.
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.
Management
Avoid the combination. Alternative antibiotics without QT effect: a cephalosporin or nitrofurantoin. Alternative for neuropathic pain instead of TCA: gabapentin or pregabalin.
Mechanism
Ciprofloxacin blocks CYP1A2 and lowers seizure threshold itself. Bupropion is a potent proconvulsant. Ciprofloxacin also weakly blocks CYP2B6 (a minor bupropion route).
Symptoms
Seizures (generalised tonic-clonic or focal), agitation, tremor, insomnia. Patients with prior epilepsy or eating disorders are at particular risk.
Management
Avoid the combination, especially in patients with prior epilepsy. Alternative antibiotics: a cephalosporin, nitrofurantoin, or fosfomycin (no effect on seizure threshold).
Mechanism
Additive QT prolongation (both prolong QT). Ciprofloxacin weakly blocks CYP1A2; citalopram is metabolised by CYP2C19, so the pharmacokinetic effect is minimal. The main risk is additive QT.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Alternative antibiotics: a cephalosporin or nitrofurantoin (no QT effect). If ciprofloxacin is needed: ECG before start, maintain potassium and magnesium, keep citalopram at 20 mg.
Mechanism
Additive tendon injury risk. Fluoroquinolones disrupt collagen synthesis in tendon fibres; glucocorticoids suppress repair and weaken the collagen matrix. carries a boxed warning for tendinitis and Achilles tendon rupture.
Symptoms
Pain and swelling in the Achilles tendon (less often other large tendons: biceps, rotator cuff). Sudden 'snap' and inability to bear weight indicates rupture. Symptoms typically appear within 1–4 weeks and may persist for months after withdrawal.
Management
Avoid the combination, especially in patients over 60, post-kidney-transplant, and with athletic activity. Alternative antibiotics: a cephalosporin or nitrofurantoin (no tendon effect). If ciprofloxacin is needed, limit physical activity for the entire course and 1 month after.
Mechanism
Additive QT prolongation. Dronedarone is on the list of drugs that contraindicate strong QT-prolonging antibiotics. Ciprofloxacin prolongs QT dose-dependently.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Avoid the combination. Alternative antibiotics: a cephalosporin (no QT effect) or nitrofurantoin for urinary tract infection.
Mechanism
Ciprofloxacin is a potent CYP1A2 inhibitor, the main duloxetine metabolic route. Duloxetine plasma levels rise 6-fold. Nausea, sedation, and serotonergic effects emerge.
Symptoms
Serotonin syndrome: agitation, confusion, tremor, myoclonus, hyperreflexia. Autonomic features: sweating, tachycardia, hypertension, fever. First signs appear within hours of co-administration.
Management
Avoid the combination. Alternative antibiotics without CYP1A2 effect: a cephalosporin, nitrofurantoin, or fosfomycin. If ciprofloxacin is needed, halve the duloxetine dose.
Mechanism
Additive QT prolongation. Escitalopram prolongs QT dose-dependently ( Lexapro caps at 20 mg/day); ciprofloxacin contributes more weakly but additively.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
During ciprofloxacin therapy, cap escitalopram at 10 mg/day. Alternative antibiotics: a cephalosporin or nitrofurantoin (no QT effect).
Mechanism
Ciprofloxacin disrupts insulin secretion from pancreatic β-cells and concurrently inhibits CYP2C9 – the glibenclamide metabolic route. Glibenclamide plasma levels rise, intensifying its hypoglycaemic effect. warning was issued in 2018.
Symptoms
Severe hypoglycaemia: sweating, tremor, hunger, tachycardia, confusion; severe cases progress to seizures and coma. Symptoms appear within 1–7 days, especially in older patients and chronic kidney disease.
Management
Avoid the combination. Alternative antibiotics: a cephalosporin or fosfomycin (no CYP2C9 effect and no β-cell impact). If ciprofloxacin is needed, monitor glucose 4 times daily and warn the patient about hypoglycaemia signs.
Mechanism
Dual mechanism: both prolong QT (additively), and ciprofloxacin blocks CYP1A2 – a partial haloperidol clearance route. Haloperidol levels rise.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Avoid the combination. Alternative antibiotics: a cephalosporin or nitrofurantoin. Alternative antipsychotics with minimal QT effect: olanzapine or aripiprazole.
Mechanism
Additive tendon injury risk. Fluoroquinolones disrupt collagen synthesis in tendon fibres; glucocorticoids suppress repair. carries a boxed warning for tendinitis and Achilles tendon rupture.
Symptoms
Pain and swelling in the Achilles tendon (less often other large tendons). Sudden 'snap' and inability to bear weight indicates rupture. Symptoms typically appear within 1–4 weeks and may persist for months after withdrawal.
Management
Avoid the combination, especially in patients over 60, post-kidney-transplant, and with athletic activity. Alternative antibiotics: a cephalosporin or nitrofurantoin (no tendon effect). If ciprofloxacin is needed, limit physical activity for the entire course and 1 month after.
Mechanism
Additive tendon injury risk. Fluoroquinolones disrupt collagen synthesis in tendon fibres; glucocorticoids suppress repair. carries a boxed warning for tendinitis and Achilles tendon rupture.
Symptoms
Pain and swelling in the Achilles tendon (less often other large tendons). Sudden 'snap' and inability to bear weight indicates rupture. Symptoms typically appear within 1–4 weeks.
Management
Avoid the combination, especially in patients over 60 and athletes. Alternative antibiotics: a cephalosporin or nitrofurantoin (no tendon effect). If ciprofloxacin is needed, limit physical activity for the whole course and 1 month after.
Mechanism
Ciprofloxacin strongly inhibits CYP1A2 – the main theophylline metabolic route. Theophylline plasma levels rise 2- to 3-fold. Theophylline has a narrow therapeutic window, so any rise is clinically significant.
Symptoms
Nausea, tachycardia, tremor, insomnia, agitation. At levels above 30 mg/L: seizures and ventricular arrhythmias. Older patients and chronic kidney disease: earlier symptoms.
Management
Avoid the combination. Alternative antibiotics: a cephalosporin or levofloxacin (weaker CYP1A2 inhibition). If ciprofloxacin is needed, halve theophylline and check level at 3–5 days.
Sources
Mechanism
Dual risk: both drugs lower the seizure threshold. Ciprofloxacin also blocks CYP1A2 (a minor tramadol activation route) and weakly affects serotonergic activity.
Symptoms
Seizures, especially in patients with prior epilepsy or head injury. Serotonin syndrome may occur with other serotonergics on board (agitation, tremor, hyperthermia).
Management
Avoid the combination in patients with prior epilepsy. Alternative antibiotics: a cephalosporin or nitrofurantoin (no seizure threshold effect). Alternative analgesics: paracetamol, an NSAID, or morphine.
Mechanism
Ciprofloxacin blocks CYP1A2 and, to a lesser extent, CYP3A4 – warfarin clearance routes. It also suppresses vitamin K-producing gut flora. INR rises 1.5- to 2-fold within 5–7 days of co-administration.
Symptoms
Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage. Risk rises in patients over 65 and with prior peptic ulcer disease.
Management
During ciprofloxacin therapy, empirically reduce warfarin by 20%; check INR 3–5 days after starting and 7 days after stopping the antibiotic. Alternatives: cephalosporin or nitrofurantoin (minimal CYP impact).
Mechanism
Old experimental data suggested NSAIDs combined with fluoroquinolones increase CNS excitability and seizure risk (via GABAergic suppression). Clinical data are very limited.
Symptoms
Mostly asymptomatic. In patients with prior epilepsy or head injury: rare seizure cases.
Management
The combination is acceptable in patients without prior epilepsy. In epilepsy or eating disorders: alternative antibiotics (a cephalosporin, nitrofurantoin) and paracetamol for analgesia.
Sources
Mechanism
Ciprofloxacin weakly affects CYP3A4 and P-glycoprotein — the main clearance routes of apixaban. It also suppresses vitamin K-producing gut flora. Additive bleeding risk.
Symptoms
Gum bleeding, epistaxis, bruising without trauma, black or tarry stools, haematuria. Higher risk in older patients, prior peptic ulcer disease, and chronic kidney disease.
Management
For short ciprofloxacin courses (5–7 days), do not change the apixaban dose but monitor for bleeding signs. In patients over 75 or with creatinine clearance below 50 mL/min, choose an alternative antibiotic without P-glycoprotein effect — ceftriaxone, cefixime, amoxicillin-clavulanate.
Mechanism
Ciprofloxacin is a weak CYP3A4 inhibitor. Atorvastatin plasma levels may rise slightly during short ciprofloxacin courses.
Symptoms
Usually no changes. In patients with myopathy risk factors: rare muscle pain.
Management
For short ciprofloxacin courses (5–7 days), no special adjustment. In patients with myopathy risk factors, check creatine kinase on muscle symptoms.
Mechanism
Dual antibiotic therapy with additive QT prolongation. Used in severe infections (e.g., empirical therapy for community-acquired pneumonia in older patients at risk of atypical flora).
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Rarely: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
The combination is appropriate in inpatient settings for indications (severe pneumonia, abdominal sepsis). ECG before start and at day 2 of therapy. Maintain potassium and magnesium. Avoid dual therapy in outpatient infections.
Mechanism
Fluoroquinolone plus systemic glucocorticoid — tendinitis and tendon rupture risk (mainly Achilles tendon). The effect is amplified at age over 60, chronic kidney disease, and organ transplantation. Inhaled budesonide does not clinically affect risk.
Symptoms
Pain in the Achilles or other tendons, swelling, impaired function. Symptoms appear in the first weeks after starting ciprofloxacin and may persist for months after stopping.
Management
On systemic budesonide, choose a non-fluoroquinolone antibiotic: cephalosporin, amoxicillin-clavulanate, doxycycline. If a fluoroquinolone is unavoidable, advise the patient to limit physical activity during and for a month after the course. If tendon pain appears, stop ciprofloxacin. Inhaled budesonide with ciprofloxacin is safe.
Mechanism
Calcium forms insoluble chelates with ciprofloxacin in the gut. Antibiotic bioavailability falls by 40–50%, raising the risk of clinical failure.
Symptoms
Persistent fever, infection symptoms, and inflammation markers 48–72 hours after antibiotic start.
Management
Take ciprofloxacin 2 hours before or 6 hours after calcium carbonate. Apply the same interval for iron, zinc, magnesium, and aluminium-containing antacids. If timing separation is impossible (e.g. continuous calcium need), choose an alternative antibiotic (amoxicillin-clavulanate, a cephalosporin).
Mechanism
Ciprofloxacin is a weak P-glycoprotein inhibitor and may slightly raise colchicine levels. Clinically significant colchicine toxicity is rare, mainly in chronic kidney disease.
Symptoms
Nausea, vomiting, diarrhoea, muscle weakness, paraesthesias. With severe toxicity: myopathy, neuropathy, bone marrow suppression.
Management
For short ciprofloxacin courses (5–7 days) with normal renal function, no colchicine adjustment needed. With creatinine clearance below 50 mL/min, halve the colchicine dose or pause it. In gout patients needing an antibiotic, alternative: a cephalosporin (no P-glycoprotein effect).
Mechanism
In 10–15% of patients, gut flora (mainly Eubacterium lentum) metabolises part of digoxin to inactive products. Ciprofloxacin suppresses this flora — digoxin levels rise by 30–80% in those patients, increasing toxicity risk.
Symptoms
Nausea, vomiting, loss of appetite, confusion, yellow-green halos around lights, arrhythmia (bigeminy, AV block). Symptoms appear earlier in older patients and chronic kidney disease.
Management
For short ciprofloxacin courses (5–7 days), most patients need no adjustment. In older patients and chronic kidney disease, check digoxin level at 5–7 days after antibiotic start. With toxicity signs, reduce dose by 25%. Alternative antibiotics: a cephalosporin (minimal gut flora impact).
Sources
Mechanism
Fluoroquinolones disturb glucose homeostasis — they can cause both hypoglycaemia (especially in older patients on glucose-lowering therapy) and hyperglycaemia. The mechanism involves pancreatic beta-cell effects.
Symptoms
Hypoglycaemia: sweating, tremor, hunger, confusion at glucose below 3.9 mmol/L. Hyperglycaemia: thirst, polyuria, fatigue.
Management
For short ciprofloxacin courses (5–7 days) on metformin, intensify glucose self-monitoring (twice daily) for the first week. In older patients and diabetics on insulin or sulfonylureas, choose an alternative antibiotic (cephalosporin, amoxicillin-clavulanate).
Mechanism
Ciprofloxacin absorbs better in acidic gastric environment. Omeprazole raises gastric pH — ciprofloxacin bioavailability drops by 20–30%. Clinically significant in infections with borderline pathogen sensitivity.
Symptoms
In severe infection: inadequate clinical response — persistent fever, symptoms, and inflammation markers 48–72 hours after antibiotic start.
Management
On the combination, take ciprofloxacin 2 hours before or 6 hours after omeprazole. If dosing cannot be separated, alternative antibiotics: amoxicillin-clavulanate for respiratory infections, a cephalosporin for UTIs. In urinary infections, ciprofloxacin still reaches adequate urine concentrations regardless of bioavailability.
Sources
Mechanism
Both prolong QT. In low-risk patients the effect is clinically minor; risk rises with hypokalaemia, hypomagnesaemia, bradycardia, and concurrent QT-prolonging drugs.
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Rarely: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
For short ciprofloxacin courses (5–7 days) in young patients without cardiac disease, the combination is acceptable. In older patients, atrial fibrillation, hypokalaemia, or other QT-prolonging drugs: ECG before start, alternative antibiotics (cephalosporin, amoxicillin-clavulanate, doxycycline).
Mechanism
No clinically significant direct interaction. Ciprofloxacin weakly inhibits CYP3A4, which partly metabolises amlodipine. Amlodipine levels may rise slightly.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
For short ciprofloxacin courses (5–7 days), no adjustment needed. In older patients, watch for leg oedema and dizziness in the first week.
Mechanism
The historical theory of reduced combined oral contraceptive efficacy via gut flora suppression is rejected by meta-analyses. Ciprofloxacin does not induce CYP3A4 and does not affect ethinylestradiol metabolism.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
Additional contraception during short ciprofloxacin courses is not needed. The old "use a barrier method for the whole cycle" advice is outdated.
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Boxed warning
FDA black box: fluoroquinolones cause potentially irreversible serious adverse effects – tendinitis and tendon rupture, peripheral neuropathy, CNS effects. Also increased risk of aortic dissection. Do not prescribe for uncomplicated infections when alternatives exist.
FDA category C. Animal studies show cartilage damage. Contraindicated in pregnancy. Used only for life-threatening infections with no alternatives.
Compatible with caution. Hale L3. RID about 2-3%, moderate transfer into milk. Older concerns about infant arthropathy were not confirmed in human observational data; AAP and Hale consider it compatible. Possible diarrhoea and candidiasis in the infant. The 2019 AEMPS alert on fluoroquinolone restrictions in adults (tendinopathy, aortic aneurysm) does not apply directly to lactation.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Ciprofloxacin is evaluated for the following indications with varying evidence strength: Urinary tract infection (evidence tier A), Traveler's diarrhea (evidence tier B), Community-acquired pneumonia (evidence tier C). See the full indication matrix with dosing and citations above on this page.
Common side effects of Ciprofloxacin (≥ 1 in 100): Nausea, Diarrhea, Headache, Insomnia. See the Safety section for uncommon and serious reactions.
FDA category C. FDA category C. Animal studies show cartilage damage. Contraindicated in pregnancy. Used only for life-threatening infections with no alternatives.
Compatible with caution. Hale L3. RID about 2-3%, moderate transfer into milk. Older concerns about infant arthropathy were not confirmed in human observational data; AAP and Hale consider it compatible. Possible diarrhoea and candidiasis in the infant. The 2019 AEMPS alert on fluoroquinolone restrictions in adults (tendinopathy, aortic aneurysm) does not apply directly to lactation.
Ciprofloxacin is contraindicated in: Hypersensitivity to fluoroquinolones; Concomitant tizanidine use; Age under 18 (except in specific indications). Full list in the Safety section.
FDA black box: fluoroquinolones cause potentially irreversible serious adverse effects – tendinitis and tendon rupture, peripheral neuropathy, CNS effects. Also increased risk of aortic dissection. Do not prescribe for uncomplicated infections when alternatives exist.