Creatinine comes from muscle, and patients with cirrhosis often have low muscle mass and reduced hepatic creatine synthesis. Serum creatinine can therefore look normal while glomerular filtration is reduced, and creatinine-based estimates of clearance overestimate it. For renally cleared drugs with narrow therapeutic windows, such as vancomycin, aminoglycosides and some antivirals, this leads to over-dosing. Where available, cystatin C gives a better estimate, and drug-level monitoring is the most direct safeguard.
- Treat a normal creatinine in cirrhosis with suspicion.
- Consider cystatin C where available to estimate kidney function.
- Use drug levels for narrow-therapeutic-index renally cleared drugs.
- Reassess dosing if muscle mass or nutrition changes.
Why it matters
The standard dosing estimate fails exactly where patients are most vulnerable.
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