Dialysis Dose Adjustment Calculator
Intermittent hemodialysis (HD) can remove a significant fraction of certain drugs from the body, reducing plasma concentrations below therapeutic levels. A supplemental dose is given after each dialysis session to restore drug levels. The supplemental dose is estimated as: Supplemental dose = Maintenance dose x Dialysis removal fraction (Fd). The removal fraction (Fd) is drug-specific and available from clinical references such as the FDA drug label or dedicated renal dosing references. This calculator provides an educational estimate; always verify with drug-specific resources.
Supplemental post-dialysis dose formula
Supplemental dose = Maintenance dose x Fd
Where Fd = fraction of drug removed by one dialysis session. Fd values are drug- and modality-specific. Fd is higher for drugs with small Vd, low protein binding, and small molecular weight. For drugs with large Vd (e.g., digoxin, amiodarone), dialysis removes negligible amounts and no supplemental dose is needed.
Drug dialyzability categories
- Highly dialyzable (Fd above 0.5): acyclovir, gentamicin, tobramycin, most water-soluble small molecules.
- Moderately dialyzable (Fd 0.25 to 0.5): amoxicillin, ampicillin, some cephalosporins, metronidazole.
- Poorly dialyzable (Fd below 0.25): vancomycin (Fd approximately 0.08 to 0.10 with conventional HD; higher with high-flux), phenytoin, digoxin, propranolol, warfarin.
- Not dialyzable: drugs with large Vd (greater than 2 L/kg) or high protein binding (greater than 90%).
- Always use drug-specific Fd values from the FDA label or clinical references such as Aronoff's Drug Prescribing in Renal Failure.
Dialysis dose adjustment: frequently asked questions
Why do some drugs require supplemental doses after hemodialysis?
Hemodialysis removes some drugs from the body along with uremic toxins. If a significant fraction of a drug is dialyzed out, plasma concentrations fall below therapeutic range. A supplemental post-dialysis dose restores drug levels, particularly important for antibiotics and antiepileptics that must remain above MIC or therapeutic threshold.
What factors determine drug dialyzability?
Dialyzability depends on molecular weight (small molecules are more dialyzable), protein binding (highly bound drugs are not dialyzable), volume of distribution (large Vd means most drug is in tissues, not plasma), and water solubility. Drugs with Vd below 1 L/kg, low protein binding, and small molecular weight are most dialyzable.
What is the supplemental dose fraction?
The supplemental dose fraction is the proportion of the drug body load that is removed by a dialysis session. It is drug-specific and dialysis-modality specific (IHD vs CVVH vs CVVHDF). Published dialysis drug tables from references such as Aronoff's Drug Prescribing in Renal Failure provide these fractions.
Are all drugs affected the same way by hemodialysis?
No. Drugs like gentamicin, acyclovir, and some cephalosporins are significantly removed by HD. Drugs with large Vd or high protein binding (e.g., vancomycin, digoxin, phenytoin) are poorly dialyzed and require different monitoring strategies.
Can this calculator be used for clinical dosing decisions?
No. This tool is for educational illustration only. Actual post-dialysis supplemental dosing requires drug-specific clinical references, pharmacist review, therapeutic drug monitoring, and physician oversight.
Official sources
- U.S. Food and Drug Administration: FDA Guidance: PK in Patients with Impaired Renal Function.
- NIH National Library of Medicine: Pharmacokinetics (StatPearls).
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.