Famotidine Dosing with GFR 46
Yes, famotidine can be taken with a GFR of 46 mL/min, but the dose must be reduced to prevent central nervous system toxicity and drug accumulation. 1
Specific Dosing Recommendations
For a GFR of 46 mL/min (moderate renal impairment, creatinine clearance 30-60 mL/min), reduce famotidine to a maximum of 20 mg once daily or 40 mg every other day, depending on the indication. 1
Dosing by Indication for GFR 30-60 mL/min:
- Active duodenal or gastric ulcer: 20 mg once daily OR 40 mg every other day 1
- Symptomatic non-erosive GERD: 20 mg once daily 1
- Erosive esophagitis: 20 mg once daily OR 40 mg every other day 1
- Duodenal ulcer recurrence prevention: 20 mg every other day (requires 10 mg formulation, not available as 20/40 mg tablet) 1
Why Dose Reduction is Critical
Famotidine is 70% eliminated unchanged through the kidneys, primarily via tubular secretion, making renal function the primary determinant of drug clearance. 2, 3
- The elimination half-life increases from 2.6 hours in normal renal function to 4.7 hours with moderate renal impairment (GFR 30-60 mL/min) 2
- Renal clearance of famotidine (310 mL/min in normal subjects) far exceeds glomerular filtration rate, confirming active tubular secretion as the major elimination pathway 4
- Without dose adjustment, drug accumulation occurs, significantly increasing the risk of CNS adverse reactions including confusion, delirium, hallucinations, disorientation, agitation, seizures, and lethargy 1
Critical Safety Warnings
CNS adverse reactions have been specifically reported in elderly patients and those with moderate to severe renal impairment receiving famotidine. 1
- The FDA label explicitly states that famotidine blood levels are higher in patients with renal impairment than in those with normal renal function 1
- The risk of adverse reactions is greater in patients with impaired renal function, particularly elderly patients 1
- Monitor closely for signs of CNS toxicity (confusion, altered mental status) when initiating therapy 1
Practical Implementation
Use the lowest effective dose and monitor renal function regularly. 1
- Start with 20 mg once daily rather than 40 mg every other day for simplicity and better adherence 1
- Famotidine may be taken with or without food 1
- Can be administered with antacids without significant interaction 1
- Avoid concurrent use of other nephrotoxic medications that could further compromise renal function 5
Common Pitfall to Avoid
Do not use standard dosing (40 mg once daily or 20 mg twice daily) in patients with GFR <60 mL/min. 1 This is the most common prescribing error and directly increases the risk of CNS toxicity and prolonged QT intervals 1. The FDA label provides explicit maximum dosing tables for renal impairment that must be followed 1.