Why Some Common Antibiotics Increase the Risk of Tendon Injuries

For most of us, antibiotics are a quick fix: a small pill that can chase away an infection in a matter of days. But not all antibiotics are created equal. Certain commonly prescribed drugs -- especially a group known as fluoroquinolones -- carry a lesser-known risk: they can damage tendons. From the Achilles to the shoulder, these injuries can appear during treatment or even weeks later, sometimes with sudden, intense pain

or long-lasting weakness. Doctors have documented cases of tendon ruptures and prolonged tendonitis linked to these medications, particularly in older adults or people who take corticosteroids. Knowing which antibiotics pose this risk, who is most vulnerable, and how to reduce the chance of injury can make a big difference. Understanding this balance between benefit and risk helps patients make informed decisions while still effectively fighting infections.

Fluoroquinolones, a class of antibiotics commonly prescribed for urinary tract infections, respiratory infections, and certain gastrointestinal issues, are effective at killing bacteria -- but they can also affect the body in unexpected ways. Research has shown that these drugs interfere with collagen synthesis, a key protein that gives tendons their strength and elasticity. When collagen production is disrupted, tendons

become weaker and more prone to inflammation or rupture. According to a 2024 study by Gillard and colleagues, tendon injuries affect about 1.8% of the U.S. population each year, and while relatively uncommon, they can be serious enough to require surgery or extended rehabilitation. Older adults, people who have previously taken corticosteroids, and those with kidney transplants are particularly vulnerable. Recognizing these risk factors is critical: patients experiencing unusual tendon pain while on antibiotics should contact their healthcare provider immediately rather than waiting for symptoms to worsen.

While tendon injuries from fluoroquinolones are uncommon, they are often sudden and striking. Case reports describe patients who were jogging or lifting a light object when their Achilles tendon snapped without warning -- sometimes days or even weeks

after finishing the antibiotic course. Studies suggest the risk is highest within the first month of treatment but can linger for up to six months. Symptoms often begin subtly, with mild swelling or stiffness that many people dismiss as normal soreness. However, ignoring early warning signs can lead to full ruptures, which may require surgical repair and months of rehabilitation. Understanding the timing and early symptoms allows patients and doctors to act quickly, potentially preventing serious, long-term damage.

The good news is that tendon injuries linked to fluoroquinolones are largely preventable with awareness and careful management. Doctors typically recommend avoiding these antibiotics if alternative treatments exist, especially for older adults or those already taking corticosteroids. For patients who must take them, simple precautions -- such as limiting

strenuous activity, stretching gently, and monitoring for any tendon discomfort -- can reduce the risk of rupture. Promptly reporting early symptoms, like stiffness, swelling, or

mild pain, allows clinicians to discontinue the drug and intervene before serious damage occurs. By combining careful prescribing practices with patient vigilance, the medical community can harness the benefits of these powerful antibiotics while minimizing potentially debilitating side effects.

Antibiotics are powerful tools, but their effects can reach beyond the infection they're meant to treat. Fluoroquinolones, in particular, show that even common medications can have unexpected consequences. Tendons, the strong cords that connect muscle to bone, may silently weaken under their influence, sometimes culminating in sudden pain or rupture. Awareness and timely action with healthcare providers are the best defenses: noticing early warning signs, avoiding intense physical strains, and exploring alternative treatments when possible can prevent serious injury. Ultimately, understanding how antibiotics interact with the body allows patients to make informed choices, balancing the urgent need to fight infections with the long-term goal of maintaining mobility and tendon health. Knowledge, rather than fear, is what keeps the body strong.

References

Gillard, Kristin K., et al. “Prevalence of Tendon Rupture and Tendinopathies Among Patients with Atherosclerotic Cardiovascular Disease Derived From United States Administrative Claims Data.” Cardiology and Therapy, vol. 13, no. 3, Sep. 2024, pp. 575–91, doi:10.1007/s40119-024-00374-5.

Lewis, Trevor G. “A Rare Case of Ciprofloxacin-Induced Bilateral Rupture of the Achilles Tendon.” BMJ Case Reports, vol. 2009, 2009, p. bcr08.2008.0697, doi:10.1136/bcr.08.2008.0697.

Lewis, Trevor, and Jill Cook. “Fluoroquinolones and Tendinopathy: A Guide for Athletes and Sports Clinicians and a Systematic Review of the Literature.” Journal of Athletic Training, vol. 49, no. 3, 2014, pp. 422–27, doi:10.4085/1062-6050-49.2.09.

Morales, Daniel R., et al. “Relative and Absolute Risk of Tendon Rupture with Fluoroquinolone and Concomitant Fluoroquinolone/Corticosteroid Therapy: Population-Based Nested Case-Control Study.” Clinical Drug Investigation, vol. 39, no. 2, Feb. 2019, pp. 205–13, doi:10.1007/s40261-018-0729-y.

Romanowska, Magdalena J., et al. “Fluoroquinolone-Induced Achilles Tendon Damage: Structural and Biochemical Insights into Collagen Type I Alterations.” International Journal of Molecular Sciences, vol. 26, no. 20, Oct. 2025, p. 10028, doi:10.3390/ijms262010028.

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