What this calculator does
This Gabapentin Dosage Calculator estimates a renal-adjusted total daily dose. Gabapentin is cleared almost entirely by the kidneys, so people with reduced kidney function need lower doses. The tool takes the dose you would give a patient with normal renal function and scales it by creatinine clearance (CrCl). This is an educational illustration of linear renal scaling, not a substitute for the official prescribing label or clinical judgement.
How to use it
Enter the target total daily dose for normal renal function (for example 1800 mg/day) and the patient's creatinine clearance in mL/min. CrCl is typically estimated using the Cockcroft–Gault equation. The calculator classifies the value into renal bands, applies a linear scaling factor of CrCl divided by a normal reference of 90 mL/min, and rounds the result to the nearest practical 50 mg increment.
The formula explained
The core equation is $$\text{Adjusted dose} = \text{Base dose} \times \dfrac{\text{CrCl}}{90}$$ For CrCl of 60 mL/min or greater the factor is capped at 1.0 (full dose). Below that, the factor falls proportionally with kidney function, so a patient at half of normal clearance receives roughly half the dose. The unrounded value is shown alongside the rounded, dispensable amount.
Worked example
A base dose of 1800 mg/day with a CrCl of 45 mL/min gives a factor of \(45 \div 90 = 0.5\). The adjusted dose is $$1800 \times 0.5 = 900 \text{ mg/day}$$ which is already a multiple of 50, so the rounded dose is 900 mg/day.
FAQ
Why 90 mL/min as normal? 90 mL/min is a common reference value for normal adult creatinine clearance, used here purely for proportional scaling.
Is this the same as the official label? No. Real gabapentin labeling uses fixed CrCl bands and specific dose ranges. This tool gives a continuous linear estimate for educational comparison.
Can I use it for patients on dialysis? No — dialysis patients require supplemental post-dialysis dosing that this simple model does not capture. Always consult a clinician and the product label.
