Gabapentin Dosage Calculator
Enter patient type, indication, weight, and kidney function to get a starting dose, maintenance range, maximum safe daily dose, and a titration schedule. Renal impairment adjustments follow the FDA Neurontin prescribing label. Pediatric weight-based dosing covers epilepsy in children aged 3-12. This tool is for educational purposes only - always confirm doses with a licensed prescriber.
What is gabapentin and what is it used for?
Gabapentin (brand name Neurontin) is an anticonvulsant and analgesic medication approved by the FDA for two primary indications: adjunctive therapy for partial seizures in adults and children aged 3 and older, and management of postherpetic neuralgia (nerve pain following shingles) in adults. It is also widely prescribed off-label for neuropathic pain from other causes (diabetic peripheral neuropathy, sciatica), fibromyalgia, restless leg syndrome, anxiety disorders, and as a sleep aid. The drug works by binding to the alpha-2-delta subunit of voltage-gated calcium channels in the central nervous system, reducing the release of excitatory neurotransmitters. Gabapentin is structurally related to the neurotransmitter GABA but does not interact directly with GABA receptors.
How gabapentin dosing works: titration and maintenance
Gabapentin is almost always started at a low dose and gradually increased (titrated) to an effective maintenance dose. A standard adult titration begins with 300 mg on Day 1, 300 mg twice daily on Day 2, and 300 mg three times daily (every 8 hours) from Day 3 onward. From that 900 mg/day baseline the dose is increased in 300 mg increments every few days as tolerated, until the patient achieves adequate symptom control or reaches the guideline maximum. For postherpetic neuralgia the effective range is typically 1800-3600 mg/day; for epilepsy it is 900-1800 mg/day in adults. The drug should not be given in doses more than 12 hours apart because very uneven spacing reduces efficacy. Stopping gabapentin should also be done gradually, reducing the dose over at least one week, to avoid withdrawal effects such as anxiety, insomnia, and nausea.
Pediatric dosing: weight-based calculation
For children aged 3-12 with epilepsy (the only FDA-approved pediatric indication), gabapentin dosing is calculated by body weight in kilograms. The starting dose is 10-15 mg/kg/day divided into three doses. Target effective doses differ by age group: children aged 3-4 are typically titrated to 40 mg/kg/day, while those aged 5-12 are titrated to 25-35 mg/kg/day. The absolute maximum is 50 mg/kg/day. A 20 kg seven-year-old, for example, might start at 200-300 mg/day and target a maintenance range of 500-700 mg/day. All pediatric doses are split into three equal administrations to maintain steady drug levels. Weight changes over time require recalculation of the dose.
Renal dose adjustment: why it matters
Gabapentin is almost entirely eliminated by the kidneys unchanged; it is not metabolised by the liver. This means that kidney impairment directly reduces drug clearance, causing gabapentin to accumulate in the body if normal doses are used. The FDA prescribing label provides specific maximum daily doses and dose frequencies based on creatinine clearance (CrCl). Patients with a CrCl below 60 mL/min require reduced doses, and those on hemodialysis need both a reduced daily dose and a supplemental dose after each four-hour dialysis session (typically 125-350 mg) to replace drug removed by dialysis. Failing to adjust doses in renal impairment can cause excessive drowsiness, ataxia, and respiratory depression. Creatinine clearance can be estimated from serum creatinine, age, weight, and sex using the Cockcroft-Gault formula.
Common side effects and drug interactions
The most common adverse effects of gabapentin are dose-dependent: somnolence (drowsiness), dizziness, ataxia (loss of coordination), fatigue, and peripheral edema. These are most pronounced when starting or increasing the dose, and many patients develop partial tolerance over several weeks. More serious concerns include respiratory depression, particularly when gabapentin is combined with central nervous system depressants such as opioids, benzodiazepines, or alcohol. The FDA added a boxed warning in 2019 highlighting this risk. Antacids containing aluminum or magnesium can reduce gabapentin absorption by up to 24% if taken too close together; gabapentin should be taken at least 2 hours after any antacid. Gabapentin also potentiates the effects of morphine, meaning lower opioid doses may be needed when the two are used together.
Gabapentin renal dose adjustment (adults)
| Kidney function | CrCl (mL/min) | Max daily dose | Max per dose | Frequency |
|---|---|---|---|---|
| Normal | >= 60 | 3600 mg | 1200 mg | Three times daily (TID) |
| Mild impairment | 30-59 | 1400 mg | 700 mg | Twice daily (BID) |
| Moderate impairment | 15-29 | 700 mg | 700 mg | Once daily |
| Severe impairment | < 15 | 300 mg | 300 mg | Once daily |
| Hemodialysis | N/A | 300 mg | 300 mg | Once daily + post-dialysis supplement |
Maximum doses based on FDA Neurontin prescribing information. All doses divided per the frequency shown.
Frequently asked questions
What is the usual starting dose of gabapentin for nerve pain?
The standard adult starting dose for neuropathic pain is 300 mg on Day 1, increasing to 300 mg twice daily on Day 2 and 300 mg three times daily (900 mg/day) from Day 3. The dose is then titrated upward in 300 mg increments every few days based on response and tolerability, up to a maximum of 3600 mg/day. Many patients with postherpetic neuralgia find effective relief in the 1800-3600 mg/day range.
How is gabapentin dosed for epilepsy in children?
Pediatric dosing for epilepsy (ages 3-12) is weight-based. The starting dose is 10-15 mg/kg/day divided into three equal doses. The target effective dose is about 40 mg/kg/day for children aged 3-4, and 25-35 mg/kg/day for children aged 5-12. The absolute maximum is 50 mg/kg/day. All doses are given every 8 hours. For example, a 30 kg ten-year-old would target roughly 750-1050 mg/day.
Do I need a lower dose of gabapentin if I have kidney disease?
Yes. Gabapentin is excreted by the kidneys unchanged, so reduced kidney function leads to drug accumulation. The FDA recommends specific dose reductions based on creatinine clearance (CrCl): a maximum of 1400 mg/day for CrCl 30-59, 700 mg/day for CrCl 15-29, and 300 mg/day for CrCl below 15. Patients on hemodialysis also need a supplemental dose of 125-350 mg after each dialysis session. Your doctor can check your CrCl with a simple blood test.
How many times a day is gabapentin taken?
For patients with normal kidney function, gabapentin is typically taken three times daily, with doses spaced no more than 12 hours apart and ideally every 8 hours to maintain steady blood levels. Patients with reduced kidney function may take it twice daily or once daily, depending on their creatinine clearance. For restless leg syndrome, a single evening dose of 600 mg is a common regimen.
Is it safe to take gabapentin with opioids?
Combining gabapentin with opioids significantly increases the risk of respiratory depression and can be life-threatening. The FDA issued a boxed warning about this interaction in 2019. If both drugs are prescribed together, both doses are usually lower than when each is used alone, and the combination requires close clinical monitoring. Always inform your prescriber about all medications you are taking.
What is the maximum safe dose of gabapentin per day?
For adults with normal kidney function, the FDA-approved maximum is 3600 mg/day (1200 mg per dose, three times daily) for most indications. However, the effective maximum varies by indication and kidney function. Patients with reduced creatinine clearance have lower ceilings ranging from 300 to 1400 mg/day. Doses above these limits have not been shown to provide additional benefit and increase the risk of serious side effects.
Can gabapentin be stopped suddenly?
No. Stopping gabapentin abruptly can cause withdrawal symptoms including anxiety, insomnia, nausea, sweating, and in patients using it for seizures, an increase in seizure frequency. The standard recommendation is to taper the dose gradually over at least one week, reducing by no more than 300 mg every 3-7 days depending on the dose and duration of use. Always consult your prescriber before reducing or stopping the medication.