Ciprofloxacin × Digoxin

In 10–15% of patients, gut flora (mainly Eubacterium lentum) metabolises part of digoxin to inactive products. Ciprofloxacin suppresses this flora — digoxin levels rise by 30–80% in those patients, increasing toxicity risk.

Nausea, vomiting, loss of appetite, confusion, yellow-green halos around lights, arrhythmia (bigeminy, AV block). Symptoms appear earlier in older patients and chronic kidney disease.

For short ciprofloxacin courses (5–7 days), most patients need no adjustment. In older patients and chronic kidney disease, check digoxin level at 5–7 days after antibiotic start. With toxicity signs, reduce dose by 25%. Alternative antibiotics: a cephalosporin (minimal gut flora impact).