To determine the pharmacokinetic properties of ciprofloxacin in the critically ill, we studied seven mechanically ventilated patients with pneumonia during entcral feedings. Subjects received ciprofloxacin 750 mg every 12 h via nasogastric tube and serial serum drug concentrations were measured after the first and fourth dose. After the initial dose, the maximum serum concentration ranged from 1.24–3.06 mg/L, and the area under the time curve from 0–12 h ranged from 3.2–19.65 mg.h/L. Similar levels were noted after dose four. Gastrointestinal absorption of ciprofloxacin in tube fed critically ill patients was decreased, but well above MIC values for many pathogenic bacteria.
Cohn, Stephen M. et. al. "Enteric Absorption of Ciprofloxacin During Tube Feeding in the Critically Ill." Journal of Antimicrobial Chemotherapy 38.5 (1996): 871-876.