Ciprofloxacin is a prescription antibiotic used to treat a wide range of bacterial infections, from urinary tract infections to serious conditions like anthrax exposure. It belongs to a class of drugs called fluoroquinolones and works by targeting two enzymes bacteria need to copy their DNA. When ciprofloxacin is present, it traps these enzymes mid-process, breaking the bacterial DNA strand and preventing the bacteria from growing or surviving.
Infections Ciprofloxacin Treats
Ciprofloxacin is FDA-approved for several types of bacterial infections. The most common reason it’s prescribed is urinary tract infections, including both simple bladder infections and more serious kidney infections. For an uncomplicated bladder infection, treatment typically lasts just 3 days. More complicated urinary tract or kidney infections may require 7 to 14 days of treatment.
Beyond UTIs, ciprofloxacin is also approved for:
- Prostate infections caused by susceptible bacteria
- Lower respiratory infections such as certain types of pneumonia and bronchitis
- Skin and soft tissue infections
- Bone and joint infections
- Abdominal infections (often paired with another antibiotic)
- Infectious diarrhea caused by specific bacteria
- Sinus infections
It’s worth noting that the FDA has urged doctors to reserve ciprofloxacin and other fluoroquinolones for infections that have no other treatment options, particularly for sinusitis, bronchitis, and uncomplicated UTIs. This is because of the drug’s serious potential side effects, which can outweigh its benefits when safer alternatives exist.
Anthrax and Plague Exposure
Ciprofloxacin plays a unique role in biodefense. It is one of the primary antibiotics stockpiled for use after anthrax exposure. If you’ve been potentially exposed to anthrax, ciprofloxacin is taken twice daily, 12 hours apart. Most people receive an initial 10-day supply, but treatment may continue for up to 60 days depending on the exposure risk. The CDC considers it a frontline drug for reducing the risk of illness and death following anthrax exposure.
Ciprofloxacin is also approved for treating plague, with a typical course of 500 to 750 mg twice daily for 14 days.
How It Works in the Body
After you take a dose, ciprofloxacin reaches its highest concentration in the blood within about 30 minutes to 1 hour. It has a half-life of 3 to 4 hours, meaning half the drug is cleared from your system in that time. This is why most prescriptions call for taking it every 12 hours, to keep levels high enough to continue killing bacteria throughout the day.
At the molecular level, ciprofloxacin attacks two targets: DNA gyrase and topoisomerase IV. These are enzymes bacteria rely on to unwind, copy, and repair their DNA. Ciprofloxacin locks onto these enzymes while they’re attached to the DNA strand, trapping them in place and leaving the DNA broken. This both stops the bacteria from multiplying and triggers cell death.
Foods and Medications That Interfere
Ciprofloxacin is unusually sensitive to what you eat and take alongside it. Dairy products reduce how much of the drug your body absorbs, and the reason is twofold: calcium in milk forms a chemical complex with the antibiotic, and milk proteins (particularly casein) physically bind to it. Research has found that casein actually has a larger effect on absorption than calcium alone at every acidity level tested.
Calcium-fortified beverages cause the same problem. Regular orange juice doesn’t affect absorption, but calcium-fortified orange juice does. Antacids and mineral supplements containing calcium, magnesium, aluminum, or iron also bind to ciprofloxacin and should be spaced at least two hours apart from your dose. If you’re taking ciprofloxacin, the simplest approach is to take it with plain water on an empty stomach or with a meal that doesn’t include dairy or mineral-heavy foods.
Serious Side Effects to Know About
Ciprofloxacin carries an FDA black box warning, the most serious safety label the agency issues, for three categories of harm.
The first is tendon damage. Fluoroquinolones increase the risk of tendinitis and tendon rupture, most commonly in the Achilles tendon but also in the shoulder, hand, and biceps. This risk exists for people of all ages and can occur during treatment or even weeks after stopping the drug. If you notice sudden pain, swelling, or a popping sensation in a tendon, stop taking the medication and avoid using that limb.
The second is peripheral neuropathy, which means nerve damage in the hands and feet. Symptoms include tingling, numbness, burning, or weakness. This nerve damage can start during treatment and may be permanent in some cases.
The third category covers effects on the brain and nervous system. These range from relatively common reactions like dizziness, insomnia, and anxiety to rarer but more alarming ones: confusion, hallucinations, tremors, seizures, paranoia, and depression. Some people experience nightmares or agitation. These effects can appear even in people with no psychiatric history.
Typical Dosing Patterns
Ciprofloxacin comes in standard tablets, extended-release tablets, and a liquid suspension. The dose and duration depend entirely on the type of infection being treated. For most general infections, adults take 250 to 750 mg twice daily. Here’s how common conditions break down:
- Uncomplicated bladder infection: 500 mg once daily (extended-release) for 3 days
- Kidney infection: 1,000 mg once daily (extended-release) or 250 to 500 mg twice daily for 7 to 14 days
- Anthrax exposure: 500 mg twice daily for up to 60 days
- Plague: 500 to 750 mg twice daily for 14 days
Shorter courses at lower doses are generally used for simpler infections, while longer, higher-dose regimens are reserved for deep-seated or life-threatening conditions. Your prescriber will choose the dose based on the infection site, severity, and which bacteria are likely responsible.