Gabapentin is unusual among common neuropathic-pain and anticonvulsant medications: it is not metabolized by the liver at all. Nearly the entire dose leaves the body unchanged through the kidneys, which means a patient's kidney function — not their weight, age, or liver enzymes — is the single biggest driver of an appropriate dose. This calculator applies the FDA's own renal dose-adjustment table so a reduced creatinine clearance is never overlooked.
Why kidney function drives the dose
Most oral drugs are cleared by a mix of liver metabolism and kidney excretion, so a patient with reduced kidney function often still clears a meaningful fraction of the dose through the liver. Gabapentin has no such backup route — it is renally cleared, unchanged. As creatinine clearance (CrCl) falls, the drug's half-life stretches and steady-state blood levels climb for any fixed dose, raising the risk of sedation, dizziness, and ataxia.
The FDA label addresses this directly with a single dose-adjustment table: the same 5-step per-dose ladder is kept, but the frequency drops from three times daily (CrCl ≥60 mL/min) to twice daily, then once daily, as CrCl declines — which is what actually shrinks the total daily dose at each step.
The titration schedule — and its limit
For patients with normal renal function, the label's postherpetic-neuralgia schedule is explicit: 300 mg on day 1, 600 mg/day on day 2, 900 mg/day on day 3, then further titration toward a 1,800 mg/day target maintenance dose (doses up to 3,600 mg/day have been studied, with no added benefit demonstrated above 1,800 mg/day).
Critically, the label does not publish an equivalent day-by-day ramp for patients with reduced renal function — only the steady-state maintenance ranges in the renal table. This calculator says so plainly rather than inventing a schedule: for reduced renal function, standard practice is to start at the lowest tier for the patient's CrCl band and titrate more slowly, under the prescriber's direction.
Below 15 mL/min, and hemodialysis
Below a CrCl of 15 mL/min specifically, the label goes a step further than the table: it calls for reducing the daily dose in direct proportion to CrCl relative to the 15 mL/min reference point. Its own example makes the rule concrete — a patient with a clearance of 7.5 mL/min (half of 15) should receive half the daily dose of a patient with a clearance of 15 mL/min.
Patients on hemodialysis are dosed on the lowest band's maintenance estimate, plus a supplemental dose given once after each 4-hour dialysis session, since hemodialysis removes a meaningful amount of the drug from circulation.
Limits of this calculator
This tool estimates from a single FDA-labeled table; it does not account for drug interactions, hepatic comorbidities, extended-release formulations (gabapentin enacarbil), pediatric dosing, or rapidly changing (non-steady-state) renal function, where a single CrCl estimate is unreliable. It is an educational reference only — every dose must be confirmed with a pharmacist or the current prescribing information before administering, and renally impaired or dialysis-dependent patients should have dosing directed by a nephrology-experienced prescriber.