Ciprofloxacin

Ciprofloxacin is a fluoroquinolone antibiotic. It kills a broad range of bacteria, including Gram-negative bugs and some Gram-positive ones.

It works by blocking two bacterial enzymes, DNA gyrase and topoisomerase IV. Bacteria need these enzymes to copy, read, repair, and recombine their DNA. Without them, the bacteria cannot survive.

Ciprofloxacin is licensed to treat many infections. These include urinary tract infections (UTIs), lower respiratory tract infections, bone and joint infections, and gut infections.

It also treats traveller's diarrhoea caused by enterotoxigenic E. coli, infections inside the abdomen, and certain sexually transmitted infections.

The BNF advises that ciprofloxacin should be kept in reserve. Use it only for infections that resist other antibiotics, or when first-line medicines are not suitable.

This follows the rules of antibiotic stewardship. In November 2018, the MHRA issued important safety restrictions for fluoroquinolones.

They advised that these medicines should not be given for mild or self-limiting infections. The reason is the risk of disabling, long-lasting, and possibly permanent side effects.

These can affect the muscles and bones, the nerves, and mental health. Ciprofloxacin is absorbed very well when taken by mouth (about 70-80%) and reaches effective levels in most body tissues.

Swallow the tablets whole with plenty of water. You can take ciprofloxacin with or without food. Do not take it with dairy products or drinks fortified with calcium.

Calcium binds to the drug and cuts its absorption by up to 50%. For the same reason, do not take it at the same time as antacids that contain aluminium or magnesium, or with iron supplements.

Leave a gap of at least 2 hours between these and your dose. Drink enough fluids throughout the course. This lowers the risk of crystals forming in your urine (crystalluria).

Finish the full course even if you feel better. If you miss a dose, do not take a double dose to make up for it. Just take the next dose at the usual time.

Uncomplicated UTI: 250 mg twice daily for 3 days.

Complicated UTI or pyelonephritis: 500 mg twice daily for 7-14 days.

Lower respiratory tract infections: 500 mg twice daily for 7-14 days.

Gonorrhoea (uncomplicated): 500 mg as a single dose (though ceftriaxone is now preferred first-line per BASHH guidelines).

Bone and joint infections: 500-750 mg twice daily for up to 3 months.

If your kidneys do not work well (creatinine clearance 30-60 mL/min), the highest dose is 500 mg every 12 hours.

If kidney function is very poor (<30 mL/min), reduce the dose to 250-500 mg every 24 hours. Older patients do not need a set dose change, but their kidney function should be checked carefully.

Side effects are grouped by how often they happen, using SmPC frequency data.

Common (≥1/100 to <1/10): Nausea, diarrhoea, vomiting, rash, and joint pain (arthralgia).

Uncommon (≥1/1,000 to <1/100): Headache, dizziness, trouble sleeping, changes in taste, stomach pain, wind, indigestion, raised liver enzymes, muscle pain (myalgia), itching, and thrush caused by Candida.

Rare (≥1/10,000 to <1/1,000): Inflamed or torn tendons (especially the Achilles tendon), nerve damage in the hands and feet (peripheral neuropathy), seizures, sensitivity to light, liver inflammation (hepatitis), kidney inflammation (interstitial nephritis), QT prolongation, torsade de pointes, inflamed blood vessels (vasculitis), Stevens-Johnson syndrome, and Clostridioides difficile-associated diarrhoea.

MHRA safety alert (2018): Fluoroquinolones have been linked to disabling and possibly permanent harm. This can affect the tendons, muscles, joints, nerves, and the central nervous system.

These reactions may start within hours of the first dose. They can also last for months after you stop the medicine.

The risk is higher in older patients, in those with poor kidney function, and in organ transplant patients taking corticosteroids.

The MHRA has limited fluoroquinolone use to serious or life-threatening infections, where other antibiotics will not work. Do not prescribe it for mild, self-limiting infections.

Stop it at once if you notice tendon pain, swelling, or inflammation. Stop it at the first sign of nerve problems, such as tingling, numbness, or pain.

Also stop it if you develop mental health symptoms, such as anxiety, depression, hallucinations, or thoughts of suicide.

Do not use it if you have had tendon problems linked to fluoroquinolones before. Ciprofloxacin makes seizures more likely.

Use it with care in patients with epilepsy or other conditions that raise the seizure risk. It strongly blocks the CYP1A2 enzyme.

This causes interactions with theophylline, duloxetine, and tizanidine (which must not be combined). Stay out of strong sunlight and UV light during treatment and for 48 hours after you stop.

Do not use ciprofloxacin if you are allergic to it, to other fluoroquinolones, or to any of its ingredients. Do not take it with tizanidine.

Ciprofloxacin strongly blocks the CYP1A2 enzyme, which raises tizanidine levels and can cause severe low blood pressure.

Do not give it to children and teenagers, except for a few licensed reasons, because it can damage the cartilage in joints. Do not use it during pregnancy or while breastfeeding.

A past tendon problem after taking a fluoroquinolone also means you should not use it.