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Ciprofloxacin was for decades the standard antibiotic for bladder infections and other infections — today it is a reserve antibiotic. About one in two women suffers at least one bladder infection over the course of their life (a German figure, broadly similar across Western countries), a common occasion for untargeted antibiotic use. Because of rare but serious side effects (tendon ruptures, neuropsychiatric symptoms), the EMA explicitly warned against careless use in 2019 — for uncomplicated infections, there are usually better alternatives today.
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Ciprofloxacin is a reserve antibiotic with rare but severe side effects. At the first signs of tendon pain, nerve symptoms, or mental changes, stop immediately and have it clarified medically. Last updated: May 2026.
Ciprofloxacin was for decades among the most frequently prescribed antibiotics — and is today a reserve antibiotic because of severe side effects. Below are the most important key facts for a quick orientation — the individual points are explained in detail in the following chapters.
| Property | Details |
|---|---|
| Active substance | Ciprofloxacin |
| Trade names | Ciprobay (the original preparation by Bayer), Ciloxan (eye drops), numerous ciprofloxacin generics |
| ATC code | J01MA02 |
| Substance class | Fluoroquinolone (gyrase inhibitor) — a reserve antibiotic |
| Mechanism of action | Inhibition of the bacterial DNA gyrase and topoisomerase IV → bactericidal (bacteria are killed off) |
| Bioavailability | about 70% (oral) |
| Half-life | about 4 hours (hence the 2× daily intake) |
| Excretion | Predominantly renal — dose adjustment with kidney impairment |
| Usual dosage | 250–750 mg 2× daily, depending on the infection; therapy duration as short as possible |
| Status | Reserve antibiotic (EMA/BfArM use restriction 2019) |
| Prescription status | Yes |
| Most important note | Stop immediately with tendon pain, nerve symptoms, or mental changes |
Ciprofloxacin is an antibiotic from the group of the fluoroquinolones (colloquially also "gyrase inhibitors"). It is a highly effective broad-spectrum antibiotic that works against many different bacteria — especially against gram-negative pathogens that cause, for example, urinary tract infections. For decades ciprofloxacin was one of the most frequently prescribed antibiotics of all.
In recent years, however, the standing of ciprofloxacin has fundamentally changed. Because of rare but serious and partly irreversible side effects, the European Medicines Agency EMA and the German BfArM strongly restricted the use of fluoroquinolones in 2019. Today ciprofloxacin counts as a reserve antibiotic — it should only be used when other, better-tolerated antibiotics are not an option.
This reassessment is important for patients to understand: anyone who earlier received ciprofloxacin without a problem for a simple bladder infection will today mostly get another antibiotic. This is not an omission, but an expression of a more responsible prescribing practice. This article puts into context when ciprofloxacin is still sensible, which risks it carries, and what one must watch for.
The central topic with ciprofloxacin. In 2019, EMA and BfArM, after a comprehensive safety assessment, published a Dear Doctor safety letter on fluoroquinolones — and drastically restricted their use. The reason: rare but severe, long-lasting, and partly irreversible side effects that affect above all muscles, tendons, joints, and the nervous system.
The most important consequences from this reassessment:
Ciprofloxacin inhibits two vital bacterial enzymes: the DNA gyrase and the topoisomerase IV. These enzymes are responsible for correctly unwinding, copying, and re-packing the bacterial genetic material (DNA) during cell division. Without them, the bacterium cannot multiply and dies off — ciprofloxacin therefore works bactericidally (killing bacteria).
These enzymes exist in this form only in bacteria, not in human cells — that explains the fundamentally targeted antibacterial effect. However, human cells have similar topoisomerases, and it is suspected that a partial influence on these endogenous enzymes, as well as oxidative stress and effects on the mitochondria, contribute to the typical severe side effects on tendons and nerves.
Ciprofloxacin is well absorbed after oral intake (bioavailability approx. 70 per cent), reaches high tissue levels, and is excreted predominantly via the kidneys — hence a dose adjustment with kidney impairment. The half-life is about 4 hours, which is why it is mostly taken twice daily. Ciprofloxacin is an inhibitor of the enzyme CYP1A2 — from this arise important interactions (e.g. with caffeine, theophylline).
After the reassessment, ciprofloxacin is used in a targeted way with certain infections in which its broad spectrum of action and the good tissue penetration offer a clear advantage — and just as important is the delineation of when it should no longer be used:
| Sensible use (per EMA/BfArM) | Do not use (any more) with |
|---|---|
| Complicated urinary tract infections and renal pelvic inflammation (pyelonephritis) — above all with resistances | An uncomplicated bladder infection (here fosfomycin, nitrofurantoin, or pivmecillinam first choice) |
| Certain bacterial gut infections (severe travellers' diarrhoea, certain salmonellae) | Mild to moderate respiratory infections (bronchitis, tonsillitis, sinusitis) |
| Bone and joint infections (osteomyelitis) — good bone penetration | Prevention (prophylaxis) of mild infections |
| Certain respiratory infections with special pathogens (e.g. Pseudomonas with cystic fibrosis) | Self-limiting infections that heal on their own |
| Certain soft-tissue infections | Patients with earlier severe fluoroquinolone side effects |
| Prostatitis (good prostate penetration) | When an equivalent, better-tolerated antibiotic is available |
| Severe infections with proven sensitivity, when alternatives fail | Viral infections (a cold, flu) — antibiotics do not work here anyway |
Important: the selection is today ideally made by antibiogram (resistance testing of the pathogen), to ensure that ciprofloxacin really works and is not used unnecessarily.
The dosage is governed by the kind and severity of the infection as well as the kidney function. Important: as short as possible, as long as necessary:
| Indication / situation | Dose | Duration |
|---|---|---|
| Complicated urinary tract infections | 500 mg 2× daily | depending on the course, often 7 days |
| Renal pelvic inflammation (pyelonephritis) | 500–750 mg 2× daily | 7–14 days |
| Severe infections | 750 mg 2× daily | depending on the course |
| Kidney impairment | Dose reduction corresponding to the eGFR | — |
| Therapy-duration principle | As short as medically justifiable | An unnecessarily long use raises the side-effect risk |
The core topic of this article — the rare but serious side effects that led to the reassessment. They can occur during or even only weeks to months after the therapy and in some cases be long-lasting or irreversible:
| Side effect | Clinical picture | Note |
|---|---|---|
| Tendon inflammations and tendon ruptures | Most commonly the Achilles tendon — pain, swelling, stiffness; in a severe case a sudden rupture | Possible even weeks after the end of therapy; a separate chapter |
| Peripheral neuropathy (nerve damage) | Tingling, numbness, burning, pain, or weakness in the arms/legs | Can be long-lasting or permanent — immediate stopping |
| Aortic aneurysm / aortic dissection | Bulges or tears of the main artery | Caution with the elderly, high blood pressure, vascular diseases, Marfan syndrome — with sudden violent abdominal/chest/back pain call the emergency services (112; or 999/112 in the UK) |
| Mental side effects | Confusion, restlessness, anxiety, sleep disturbances, nightmares; rarely depression, hallucinations, suicidal thoughts | With mental changes clarify medically immediately |
| Blood sugar derailments | Both under- and over-sugaring | Relevant above all in diabetics |
| QT interval prolongation | Cardiac arrhythmias | Caution with heart diseases and QT-prolonging accompanying medications |
| Severe allergic reactions | Up to anaphylaxis | With skin rash, swelling, shortness of breath call the emergency services (112; or 999/112 in the UK) |
| Severe skin reactions | Stevens-Johnson syndrome (very rare) | Immediate stopping |
| Others (rare) | Liver damage, vision disturbances, hearing disturbances | Clarify medically if they occur |
Besides the rare severe side effects, there are the more common, mostly more harmless accompanying phenomena:
An important antibiotic-typical complication is the Clostridioides difficile infection — a severe, partly bloody diarrhoea through an overgrowth with this bacterium after a disturbance of the gut flora. With severe or persistent diarrhoea during or after the therapy, always clarify medically, never simply self-treat with diarrhoea remedies (loperamide).
Because the tendon problem is so characteristic and potentially serious, it deserves particular attention. The good news: anyone who knows the warning signs and reacts early can often avoid a complete tendon rupture.
| Warning signs of impending tendon problems | What to do immediately |
|---|---|
| Pain in a tendon (most commonly the Achilles tendon — heel/calf, but also shoulder, hand) | Stop ciprofloxacin immediately and clarify medically |
| Swelling in the tendon area | Spare the affected tendon — no load, no sporting activity |
| Stiffness or restriction of movement | Do not wait — early action often prevents the rupture |
| Pain under load that was not there before | Stay attentive for weeks even after the end of therapy |
