A 62-year-old man with chronic kidney disease (eGFR 35 mL/min/1.73 m²) is prescribed a fluoroquinolone for a urinary tract infection. Which is the most common serious adverse effect he is at highest risk for?

Explanation

## Risk Factors for Fluoroquinolone Tendinopathy ### High-Risk Patient Profile **Key Point:** Tendinopathy and tendon rupture are the most common serious adverse effects in patients with specific risk factors, particularly those ≥60 years old with renal impairment, concurrent corticosteroid use, or tendon disease history. ### Risk Stratification for Tendinopathy | Risk Factor | Relative Risk Increase | Mechanism | |---|---|---| | Age >60 years | 2–3× | Reduced collagen turnover, degenerative changes | | Renal impairment (eGFR <60) | 2–4× | Fluoroquinolone accumulation; reduced clearance | | Concurrent corticosteroids | 3–5× | Collagen synthesis inhibition | | Prior tendon disease | 2–3× | Pre-existing structural weakness | | Combination of ≥2 factors | 5–10× | Multiplicative risk | ### Pathophysiology of Fluoroquinolone-Induced Tendinopathy 1. **Inhibition of topoisomerase II** in mitochondrial DNA of tendon fibroblasts 2. **Reduced collagen synthesis** and impaired cross-linking 3. **Accumulation in renal impairment** → higher tissue concentrations 4. **Inflammatory response** → tendon degeneration 5. **Rupture risk** → particularly Achilles tendon (most common site) ### Clinical Pearl: This patient has TWO major risk factors (age 62 + eGFR 35), placing him in the highest-risk category. Tendon rupture can occur even weeks after fluoroquinolone discontinuation. **High-Yield:** The FDA issued a black-box warning for fluoroquinolone-associated tendinopathy in 2008. Avoid fluoroquinolones in patients >60 years with renal impairment unless no alternatives exist. ### Management Strategy ```mermaid flowchart TD A[Patient needs fluoroquinolone]:::outcome --> B{Age >60 AND/OR eGFR <60?}:::decision B -->|Yes| C{Corticosteroids or prior tendon disease?}:::decision B -->|No| D[Standard dosing safe]:::action C -->|Yes| E[Avoid fluoroquinolone if possible]:::urgent C -->|No| F[Use with caution; counsel on tendon rupture risk]:::action E --> G[Consider alternative agent]:::action F --> H[Monitor for tendon pain/swelling]:::action G --> I[Beta-lactam, macrolide, or other class]:::outcome ``` ### Tip: When a clinical vignette specifies age >60 + renal impairment + fluoroquinolone, immediately think tendinopathy as the most likely serious adverse effect.