All of the following are true regarding fluoroquinolone-induced tendinopathy EXCEPT:

Question

Accepted Answer

D. The mechanism involves inhibition of bacterial DNA gyrase leading to direct myotendinous toxicity. ## Fluoroquinolone-Induced Tendinopathy: Mechanism and Risk Factors

### Correct Answer Analysis

**Key Point:** The mechanism of fluoroquinolone tendinopathy is NOT due to inhibition of bacterial DNA gyrase (which is the therapeutic target in bacteria). Instead, it involves inhibition of human mitochondrial topoisomerase II and interference with collagen synthesis in tendon fibroblasts.

### Pathophysiology

Fluoroquinolones cause tendon damage through:

1. **Inhibition of human mitochondrial enzymes** — particularly topoisomerase II, which is structurally similar to bacterial DNA gyrase but present in human cells
2. **Impaired collagen cross-linking** — reduced hydroxylation and glycosylation of collagen
3. **Increased apoptosis** of tendon fibroblasts
4. **Altered magnesium homeostasis** — fluoroquinolones chelate Mg²⁺, reducing cofactor availability for collagen maturation

### Risk Factors for Tendon Rupture

| Risk Factor | Details |
| --- | --- |
| **Age >60 years** | Baseline collagen degradation; reduced healing capacity |
| **Corticosteroid use** | Synergistic effect on collagen synthesis inhibition |
| **Renal impairment** | Reduced drug clearance; prolonged tissue exposure |
| **Tendon disease history** | Prior rupture, tendinitis, or rheumatologic disease |
| **Myasthenia gravis** | Fluoroquinolones can exacerbate neuromuscular weakness |
| **Fluoroquinolone type** | Older agents (ciprofloxacin, levofloxacin) > newer agents (moxifloxacin) |

### Clinical Presentation

**High-Yield:** Achilles tendon rupture is the most common serious adverse event, followed by rotator cuff and patellar tendons. Rupture can occur weeks to months after drug discontinuation.

**Clinical Pearl:** Patients often report sudden sharp pain, audible "pop," inability to plantarflex (Achilles) or abduct shoulder (rotator cuff), and swelling at the tendon site.

### Contraindications and Precautions

**Warning:** Fluoroquinolones are contraindicated or require extreme caution in:
- History of tendon rupture
- Myasthenia gravis (can precipitate myasthenic crisis)
- Concurrent high-dose corticosteroids
- Age >60 with multiple comorbidities

[cite:KD Tripathi 8e Ch 48]

Answer

A. Fluoroquinolone use should be avoided in patients with a history of tendon rupture or myasthenia gravis

Answer

B. Achilles tendon is the most commonly affected site, followed by rotator cuff tendons

Answer

C. Risk is significantly increased in patients aged >60 years and those on concurrent corticosteroids

All of the following are true regarding fluoroquinolone-induced tendinopathy EXCEPT:

Explanation

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