Which is more QT prolonging, levofloxacin or ciprofloxacin?

Ciprofloxacin Has Less QT Prolongation Effect Than Levofloxacin

Ciprofloxacin is associated with significantly less QT interval prolongation compared to levofloxacin and should be preferred in patients with risk factors for QT prolongation or Torsades de Pointes (TdP).

Comparative QT Prolongation Risk

The evidence clearly demonstrates a difference in QT prolongation risk between these two fluoroquinolones:

• Ciprofloxacin appears to have the lowest risk for QT prolongation and the lowest TdP rate among all fluoroquinolones 1.

• Levofloxacin has been shown to increase QTc interval significantly (by approximately 15.68 ± 26.84 milliseconds) in cardiac patients 2.

• A direct comparative study found that the relative risk for QTc prolongation with levofloxacin was approximately 4 times higher than ciprofloxacin in diabetic patients and 1.5 times higher in non-diabetic patients 3.

• While moxifloxacin carries the greatest risk of QT prolongation among fluoroquinolones, levofloxacin still requires caution in patients at risk for QT prolongation 1.

Clinical Evidence and Guidelines

The British Thoracic Society guidelines acknowledge that moxifloxacin and, to a lesser extent, levofloxacin prolong the QT interval 4. The guidelines specifically state that levofloxacin is generally preferred over moxifloxacin for fewer adverse events and less QTc prolongation 4.

A prospective study examining ciprofloxacin's effect on QTc interval in ICU patients (who typically have multiple comorbidities) found no significant QTc prolongation. In fact, there was a slight shortening of the QTc interval during or after ciprofloxacin infusion 5.

Risk Factors and Precautions

When prescribing either fluoroquinolone, consider these important risk factors for QT prolongation:

• Pre-existing cardiac conditions
• Electrolyte disturbances (particularly hypokalemia)
• Concomitant use of other QT-prolonging medications
• Advanced age
• Female gender
• Renal dysfunction

Clinical Decision Algorithm

1. For patients with NO risk factors for QT prolongation:

   • Either ciprofloxacin or levofloxacin can be used based on the infection being treated and local susceptibility patterns

2. For patients with ANY risk factors for QT prolongation:

   • Choose ciprofloxacin as the preferred fluoroquinolone
   • Obtain baseline ECG before starting therapy
   • Monitor electrolytes, particularly potassium and magnesium

3. For patients requiring a fluoroquinolone who have:

   • History of arrhythmias
   • Congenital long QT syndrome
   • Baseline QTc > 500 ms
   • Multiple QT-prolonging medications
   • Consider alternative antibiotic classes if possible
   • If fluoroquinolone necessary, use ciprofloxacin with ECG monitoring

Additional Considerations

• Diabetic patients appear to be at higher risk for QTc prolongation with levofloxacin compared to ciprofloxacin 3.

• Levofloxacin is also associated with a higher risk of dysglycemia (both hyperglycemia and hypoglycemia) compared to ciprofloxacin 3.

• When treating tuberculosis, guidelines note that levofloxacin is generally preferred over moxifloxacin for fewer adverse events and less QTc prolongation, but do not specifically compare levofloxacin to ciprofloxacin for TB treatment 4.

In conclusion, while both antibiotics are generally safe, the evidence consistently shows that ciprofloxacin has a more favorable cardiac safety profile regarding QT prolongation compared to levofloxacin.