Renal Dose Adjustment Calculator

This calculator takes an already-known estimated glomerular filtration rate (eGFR, in mL/min/1.73m^2) as a direct input -- it does not calculate eGFR itself, so it is not a Cockcroft-Gault or CKD-EPI creatinine-clearance calculator; those formulas need serum creatinine, age, sex, and body weight, none of which this tool asks for. eGFR and creatinine clearance (CrCl) are related but not interchangeable: eGFR (from CKD-EPI or MDRD) is normalized to a standard 1.73m^2 body surface area and is the figure most lab reports return, while CrCl (from Cockcroft-Gault) is NOT BSA-normalized and is the figure many drug labels' dosing tables were originally built around -- entering a raw CrCl value (in mL/min, no BSA normalization) into this eGFR field can misstage a patient, especially at very high or low body weights where the two diverge most. What this tool does with whatever GFR figure you enter is bucket it into one of five kidney-function stages (Normal at 90 and above, Mild from 60 to 89, Moderate from 30 to 59, Severe from 15 to 29, and ESRD below 15 mL/min/1.73m^2) -- cutoffs that match the older K/DOQI 2002 CKD staging system, not the current KDIGO 2012/2024 system, which further splits the 30-59 Moderate band into G3a (45-59) and G3b (30-44) -- then apply a flat percentage dose reduction and interval extension at each stage: no change through Mild, a 25% dose cut with a 1.5x longer interval at Moderate, a 50% cut with a 2x interval at Severe, and a 75% cut with a 3x interval at ESRD. Critically, Dose Reduction only reports the per-dose cut -- because the interval is ALSO extended, fewer doses are given per day, and the two effects compound: Combined Daily Exposure Reduction is the number that reflects total drug exposure, and it is always larger than Dose Reduction alone (50% vs. the 25% Dose Reduction figure at Moderate; roughly 91.7% vs. the 75% Dose Reduction figure at ESRD, since 0.25x dose at 1/3 the daily frequency leaves only about 8.3% of normal daily exposure).

Those specific percentages are round, illustrative numbers built into this tool, not a citation to any single drug's dosing label -- real renal dose adjustment for a given medication depends on how much of that exact drug is cleared by the kidney versus other routes, its therapeutic index, and its dialyzability, all of which are published per-drug, not as one universal formula. Normal Dose is what actually moves Adjusted Dose at any fixed kidney-function stage, since the stage only changes a multiplier applied to whatever dose you enter; Normal Dosing Interval plays no part in Adjusted Dose at all, only in Adjusted Interval. eGFR itself has no effect on either output until it drops below 60 -- above that this calculator makes no adjustment, matching its Mild-stage rule.