Levothyroxine with Ciprofloxacin Interaction Details

Brand Names Associated with Levothyroxine

Brand Names Associated with Ciprofloxacin

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Nov 19, 2023

Interaction Effect

Decreased efficacy of levothyroxine

Interaction Summary

The American Association of Clinical Endocrinologists and American Thyroid Association list ciprofloxacin as capable of interfering with absorption of levothyroxine and recommend against coadministration. In a double-blind, randomized, crossover study (n=8), thyroxine AUC was decreased by 39% with concurrent oral doses of ciprofloxacin and levothyroxine . Thyroid stimulating hormone levels were increased in 2 patients on stable levothyroxine therapy after multi-week administration of oral ciprofloxacin . Administer levothyroxine at least 4 hours before or after drugs that are known to interfere with absorption  and closely monitor thyroid status in patients receiving concurrent ciprofloxacin and levothyroxine .

Severity

Moderate

Onset

Rapid

Evidence

Probable

How To Manage Interaction

Ciprofloxacin can interfere with absorption of levothyroxine. Administer levothyroxine at least 4 hours before or after drugs that are known to interfere with absorption  and closely monitor thyroid status in patients receiving concurrent ciprofloxacin and levothyroxine therapy .

Mechanism Of Interaction

Interference with absorption of levothyroxine

Literature Reports

A) During a prospective, double-blind, randomized study in healthy adult volunteers (n=8), mean baseline-corrected thyroxine (T4) AUC was decreased by 39% with coadministration of ciprofloxacin and levothyroxine compared with crossover treatment with placebo and levothyroxine (p=0.035). Study doses were levothyroxine 1000 mcg orally and ciprofloxacin 750 mg orally. The washout period between study days was at least 4 weeks. Total plasma T4 concentrations were measured over a 6-hour period after dosing .

B) Two cases of unexplained hypothyroidism were reported in patients previously stable on levothyroxine who received oral ciprofloxacin for treatment of infection. In an 80-year-old woman with advanced thyroid cancer, thyroid stimulating hormone (TSH) was increased to 44 milli-international units/L following 4 weeks of ciprofloxacin 750 mg twice daily for treatment of osteomyelitis. Increase of her standard dose of levothyroxine 125 mcg/day to 200 mcg/day was ineffective, but thyroid function tests returned quickly to normal after discontinuation of ciprofloxacin. In a 79-year-old woman with a stable daily dose of levothyroxine 150 mcg, TSH increased from 1.6 to 19 milli-international units/L following 3 weeks of treatment with ciprofloxacin 500 mg twice daily for a wound infection. Thyroid function normalized in this patient with a switch from concomitant administration of the 2 drugs to a 6-hour separation .

Levothyroxine Overview

• Levothyroxine is used to treat hypothyroidism (condition where the thyroid gland does not produce enough thyroid hormone). It is also used with surgery and radioactive iodine therapy to treat thyroid cancer. Levothyroxine is in a class of medications called hormones. It works by replacing thyroid hormone that is normally produced by the body.

• Without thyroid hormone, your body cannot function properly, which may result in poor growth, slow speech, lack of energy, excessive tiredness, constipation, weight gain, hair loss, dry, thick skin, increased sensitivity to cold, joint and muscle pain, heavy or irregular menstrual periods, and depression. When taken correctly, levothyroxine reverses these symptoms.

Ciprofloxacin Overview

• Ciprofloxacin is used to treat or prevent certain infections caused by bacteria such as pneumonia; gonorrhea (a sexually transmitted disease); typhoid fever (a serious infection that is common in developing countries); infectious diarrhea (infections that cause severe diarrhea); and infections of the skin, bone, joint, abdomen (stomach area), and prostate (male reproductive gland), Ciprofloxacin is also used to treat or prevent plague (a serious infection that may be spread on purpose as part of a bioterror attack) and inhalation anthrax (a serious infection that may be spread by anthrax germs in the air on purpose as part of a bioterror attack). Ciprofloxacin may also be used to treat bronchitis, sinus infections, or urinary tract infections but should not be used for bronchitis and sinus infections, or certain types of urinary tract infections if there are other treatment options. Ciprofloxacin extended-release (long-acting) tablets are used to treat kidney and urinary tract infections; however, some types of urinary tract infections should only be treated with ciprofloxacin extended release tablets if no other treatment options are available. Ciprofloxacin is in a class of antibiotics called fluoroquinolones. It works by killing bacteria that cause infections.

• Antibiotics such as ciprofloxacin will not work for colds, flu, or other viral infections. Using antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.