Preoperative Famotidine Dosing for Aspiration Pneumonia Prevention
For patients at increased risk of pulmonary aspiration, oral famotidine 40 mg administered at least 3 hours before surgery is recommended to reduce gastric volume and increase gastric pH, thereby decreasing aspiration risk. 1
Famotidine Administration Options and Timing
Oral Administration
- Oral famotidine 40 mg should be administered at least 3 hours before surgery for optimal effect in reducing gastric acidity 2, 3
- For maximum effectiveness, oral famotidine can be given both the night before surgery and on the morning of surgery 2
- Single-dose oral famotidine has been shown to effectively reduce gastric volume and increase gastric pH, comparable to double-dose oral ranitidine 4
Parenteral Administration
- Intravenous famotidine 20 mg administered 15-30 minutes before endotracheal intubation effectively decreases gastric fluid volume and increases gastric pH 5
- Intramuscular famotidine 20 mg administered 1 hour before endotracheal intubation provides similar effectiveness to IV administration 5, 2
- Administering intramuscular famotidine less than 15 minutes before intubation produces inadequate suppression of gastric secretion 5
Efficacy and Duration of Action
- Placebo-controlled randomized controlled trials indicate that orally-administered famotidine is effective in reducing gastric volume and acidity during the perioperative period (Category A2-B evidence) 1
- Intramuscular famotidine has similar efficacy according to placebo-controlled RCT evidence (Category A3-B evidence) 1
- Both IV and IM famotidine provide suppression of gastric secretion for over 4 hours 5
- Famotidine administration significantly decreases the percentage of patients considered "at risk" (defined as pH < 2.5 and gastric volume > 25 mL) 1, 2, 3
Patient Selection
- Histamine-2 receptor antagonists like famotidine should not be routinely administered to all patients but reserved for those at increased risk of pulmonary aspiration 1
- Risk factors for aspiration include emergency surgery, obesity, pregnancy, difficult airway, gastroesophageal reflux disease, and delayed gastric emptying 1
Common Pitfalls and Considerations
- Administering famotidine too close to induction (less than 15 minutes for IV or less than 1 hour for IM) may not provide adequate protection 5
- Single-dose oral famotidine given the evening before surgery (approximately 10 hours before induction) is not reliable for decreasing intragastric acidity during induction 6
- Famotidine should be part of a comprehensive aspiration prevention strategy that includes appropriate fasting guidelines (6 hours for light meals, 8 hours for fatty meals) 1
- The literature is insufficient to evaluate the direct effect of histamine-2 receptor antagonists on perioperative pulmonary aspiration or emesis/reflux, though they effectively modify the risk factors 1