What are 5 drugs that interact with ciprofloxacin?

October 7, 2025 •

3 min read

Ciprofloxacin is a widely prescribed antibiotic, but its effectiveness and safety can be significantly impacted by interactions with other medications. Knowing what are 5 drugs that interact with ciprofloxacin is critical for patients to avoid serious complications like reduced antibiotic efficacy, increased bleeding risk, or life-threatening side effects.

Quick Summary

This article details five major drugs that interact with ciprofloxacin, explaining how these interactions occur and the potential consequences. It covers management strategies and precautions for patients on antacids, tizanidine, warfarin, theophylline, and methotrexate, emphasizing the importance of professional medical advice.

Key Points

Antacids can reduce ciprofloxacin effectiveness: Avoid taking antacids or mineral supplements containing calcium, magnesium, or aluminum within 2 to 6 hours of a ciprofloxacin dose to ensure proper absorption.
Tizanidine and ciprofloxacin are contraindicated: The combination of the muscle relaxant tizanidine and ciprofloxacin is dangerous and should be avoided entirely due to risks of severe hypotension and sedation.
Warfarin risk of increased bleeding: Ciprofloxacin can increase the blood-thinning effect of warfarin, necessitating close monitoring of INR levels to prevent dangerous bleeding.
Theophylline interaction can be fatal: Theophylline levels can increase dangerously when taken with ciprofloxacin, potentially leading to seizures or cardiac arrest; co-administration should be avoided.
Methotrexate levels can increase: Concomitant use with ciprofloxacin can increase methotrexate levels in the body, raising the risk of severe toxicity.
Check with healthcare professionals: Always inform your doctor or pharmacist about all medications, supplements, and vitamins you are taking before starting a course of ciprofloxacin.

Ciprofloxacin is a powerful and widely used fluoroquinolone antibiotic prescribed to treat a variety of bacterial infections, such as those affecting the urinary tract, skin, and respiratory system. However, a crucial aspect of using this medication safely is understanding its potential for drug-drug interactions. These interactions can alter the effectiveness of ciprofloxacin, increase the risk of adverse effects from other medications, or lead to entirely new health risks. Always consult a healthcare provider or pharmacist before starting ciprofloxacin and inform them of all other medications and supplements being taken.

5 Major Drugs That Interact with Ciprofloxacin

Here are five significant drug interactions to be aware of when taking ciprofloxacin. Each interaction is explained with its specific mechanism and potential health risks.

1. Antacids and Mineral Supplements

Antacids and supplements containing polyvalent cations like calcium, magnesium, aluminum, iron, and zinc can interact with ciprofloxacin by binding to it in the gastrointestinal tract, forming a complex that reduces its absorption. This can significantly decrease ciprofloxacin's effectiveness. To manage this interaction, take ciprofloxacin at least 2 hours before or 6 hours after these products.

2. Tizanidine (Zanaflex)

The muscle relaxant tizanidine interacts severely with ciprofloxacin. Ciprofloxacin inhibits the enzyme that metabolizes tizanidine, leading to a significant increase in tizanidine levels in the body. This can cause dangerous side effects like extreme sedation, low blood pressure, and a slow heart rate, making concurrent use contraindicated. Alternative medications should be used if both are needed.

3. Warfarin (Coumadin)

Ciprofloxacin can increase the effects of the blood thinner warfarin, raising the risk of bleeding. Ciprofloxacin affects how the body processes warfarin, increasing its concentration. This heightened anticoagulant effect can lead to increased bruising and the potential for serious internal bleeding. If these medications must be taken together, close monitoring of blood clotting levels (INR) and potential warfarin dose adjustments are required.

4. Theophylline

Theophylline, used for breathing conditions, can reach dangerously high levels when taken with ciprofloxacin. Ciprofloxacin inhibits the enzyme responsible for breaking down theophylline. Elevated theophylline levels can lead to severe, potentially fatal reactions like seizures and cardiac arrest. Co-administration is generally avoided, and if used, requires strict monitoring and dose adjustments.

5. Methotrexate

Taking methotrexate with ciprofloxacin can increase the amount of methotrexate in the body, potentially causing toxicity. Ciprofloxacin can interfere with the kidneys' ability to remove methotrexate. Higher methotrexate levels can cause severe side effects affecting bone marrow, the digestive system, liver, or kidneys. Caution and monitoring are necessary if these drugs are co-administered, especially in patients with kidney problems or on high methotrexate doses.

Comparison of Ciprofloxacin Drug Interactions


Interacting Drug	Interaction Type	Mechanism of Interaction	Potential Risk	Management Strategy
Antacids & Minerals	Reduced absorption	Chelation of ciprofloxacin by polyvalent cations (calcium, magnesium).	Decreased effectiveness of ciprofloxacin, potentially leading to treatment failure.	Separate administration time by at least 2 hours before or 6 hours after.
Tizanidine	Increased drug levels	Ciprofloxacin inhibits CYP1A2 enzyme, which metabolizes tizanidine, causing accumulation.	Severe sedation, dangerously low blood pressure, or slow heart rate.	Contraindicated; avoid using together entirely.
Warfarin	Increased anticoagulant effect	Ciprofloxacin affects warfarin metabolism, increasing its concentration.	Increased risk of bleeding, from bruising to internal hemorrhage.	Close monitoring of INR levels and potential dose adjustment.
Theophylline	Increased drug levels	Ciprofloxacin inhibits CYP1A2 enzyme, preventing theophylline breakdown.	Serious and potentially fatal reactions, including seizures and cardiac arrest.	Avoid concurrent use if possible; otherwise, strict monitoring and dose adjustment.
Methotrexate	Increased drug levels	Ciprofloxacin inhibits renal clearance of methotrexate.	Severe methotrexate toxicity, affecting bone marrow, liver, and kidneys.	Cautious use with monitoring of methotrexate levels; potential dose adjustment.

Other Considerations and Conclusion

Beyond these five key interactions, ciprofloxacin can interact with other drugs and even certain foods. For instance, caffeine consumption should be limited while on ciprofloxacin, as it can heighten the effects of caffeine, causing anxiety, insomnia, and palpitations. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen can increase the risk of seizures when taken with high doses of ciprofloxacin. Certain antiarrhythmics and antidepressants can also increase the risk of a dangerous irregular heart rhythm known as QT prolongation when combined with ciprofloxacin. The combination of ciprofloxacin with milk and other dairy products should also be spaced out, similar to antacids, to ensure proper absorption.

The takeaway is clear: medication interactions are a serious concern, and patients should always inform their doctor and pharmacist of their complete medication and supplement list. Proactive communication and careful management can help prevent adverse events and ensure safe and effective treatment. For more comprehensive information, resources like MedlinePlus offer detailed drug information.

Frequently Asked Questions

Antacids containing polyvalent cations like aluminum, magnesium, and calcium bind to ciprofloxacin in the stomach, forming an insoluble complex that prevents the antibiotic from being absorbed properly into the bloodstream. This can make ciprofloxacin less effective in treating your infection.

Tizanidine and ciprofloxacin are contraindicated because ciprofloxacin inhibits the CYP1A2 enzyme, which breaks down tizanidine. This leads to a significant increase in tizanidine levels, causing severe side effects like dangerously low blood pressure and extreme sedation.

Taking warfarin with ciprofloxacin increases the risk of bleeding. Ciprofloxacin interferes with warfarin's metabolism, increasing its concentration in the blood and enhancing its blood-thinning effects. Close monitoring of blood clotting time (INR) is necessary.

You may be advised to limit or avoid caffeine while taking ciprofloxacin. Ciprofloxacin can slow down the body's metabolism of caffeine, which can intensify caffeine's effects and lead to side effects like nervousness, insomnia, and heart palpitations.

The combination can lead to increased levels of methotrexate in the body, which can result in toxicity. This happens because ciprofloxacin can reduce the kidney's ability to clear methotrexate. Patients, especially those on high doses or with kidney issues, need careful monitoring.

You should avoid taking ciprofloxacin with dairy products like milk, cheese, or yogurt alone. The calcium in dairy can interfere with absorption. However, you can consume dairy as part of a larger meal. It is generally recommended to separate your ciprofloxacin dose from dairy by at least 2 hours.

Yes, ciprofloxacin can interact with other antibiotics. For example, some macrolide antibiotics (like erythromycin) can increase the risk of QT prolongation, a type of irregular heartbeat, when taken with ciprofloxacin.