The 300 mg capsule does not change. The interval does
Gabapentin is excreted unchanged by the kidney. Dose tables in the Neurontin label are built on creatinine clearance, often estimated with Cockcroft-Gault, not on how dramatic the pain sounds.
Zephyra still names 300 mg as the capsule lock. The renal glint is how often that capsule appears, and whether 100 mg units should have been dispensed instead.
The slow ramp for people with clearance at or above 60 is 300 mg slow ramp. This post is the trim. Ward sheet: gabapentin frame.
A creatinine from last winter is not a 300 mg TID licence after a ramipril start, a diarrhoeal week, or a stone of weight loss.
Half-life near 52 hours when clearance is under 30 is why one 300 mg can last until Thursday. Twitches are a hold, not a lunchtime add-on.
The 15-29 row is once-daily 200 to 700 mg. Three 300 mg clocks are off that row even if pain is loud.
Dialysis extras replace what the machine removed. They are not bonus pain tablets on a Monday.
Which number to bring
Creatinine, age, sex, and weight if you have them - Cockcroft-Gault uses those. An eGFR from the GP screen is the usual Scottish proxy. Say if you are on dialysis and which days.
Muscle mass fools creatinine. A thin older woman can have a 'normal' creatinine and a low clearance. The table still matters.
Do not use a phone eGFR app as a licence to change 300 mg without the prescriber.
- Date of last creatinine on the box.
- Current clocks: one, two, or three 300 mg.
- Dialysis days if any.
The post-dialysis extra is not a bonus pain tablet
Hemodialysis patients get a maintenance dose from the clearance estimate plus a supplemental 125 to 350 mg after each four-hour session. That extra replaces what the machine removed.
Swallowing an extra 300 mg on a non-dialysis Tuesday 'because pain flared' is not the supplemental dose.
Peritoneal dialysis is not the same table. Do not copy a haemodialysis sticker.
How a 300 mg TID script gets cut
Example: eGFR slides from 70 to 38. 300 mg three times daily (900 mg) may need to become 300 mg twice daily. The clinician writes it. You do not silently skip the afternoon capsule and call that a taper.
Example: eGFR 24. 300 mg once in the evening may be the whole prescription. Adding a morning 300 mg because nights were bad recreates a BID dose on the once-daily row.
Stopping for a procedure: still taper if you have been on regular gabapentin. Kidney impairment does not make a cliff safer.
Muscle loss makes a 'normal' creatinine look safer than it is
A thin older woman with creatinine 70 micromol/L can still sit on the 30-59 row. The 300 mg TID pain card was written for a different body.
Ask them to estimate clearance, not to glance at the creatinine as 'fine'.
Sarcopenia plus 300 mg TID is a common Edinburgh admission story. The lock stays 300 mg as the unit. The frequency must move.
If weight has dropped a stone since the script, say so. That is a renal-glint fact.
Do not celebrate a falling creatinine after illness as 'better kidneys' if it is falling muscle. Recalculate.
New ramipril plus the same 300 mg TID
ACE inhibitors and diuretics can drop eGFR in a hot week. The 300 mg TID card from March may be wrong in August.
A faint, a food-poisoning week, or a new NSAID is a reason to get creatinine before the next climb - and before you defend TID.
Do not add ibuprofen for the same nerve pain gabapentin was meant to treat. Two kidney hits.
If someone already started ramipril, say so at the gabapentin review. The table needs a new number.
Hold 300 mg and call if you suddenly look drunk on a dose that was fine last month. That is clearance, not a new personality.
Bring the blood-pressure drug list with the 300 mg box. They belong in one sentence.
Dialysis starts retire the old TID card the same week, not at the next pain clinic in November.
The blood test is three months old and the 300 mg is daily
A creatinine from last winter is not a licence for 300 mg TID August 2026 if the person has been ill, started an ACE inhibitor, or lost a lot of weight.
Ask for a dated number before any climb past 900 mg, and before you defend a 300 mg TID on an 80-year-old.
Acute intercurrent illness is when gabapentin toxicity appears: myoclonus, severe sedation, a drunk walk. Hold and get a new creatinine.
Do not wait for the next pain-clinic letter in November. The kidney does not follow that diary.
Write the creatinine date on the 300 mg box in pencil. Rub it out when a new number arrives.
Why the same 300 mg lasts until Thursday
Volunteer data after 400 mg: mean half-life about 6.5 hours when clearance was above 60, about 52 hours when clearance was under 30. Plasma clearance fell from roughly 190 to 20 mL/min.
That is why a man with eGFR 22 looks 'sensitive' on 300 mg at night and still hungover at noon two days later. He is still clearing yesterday.
Elderly dosing is renal dosing. Age is a proxy for clearance, not a separate personality trait.
Twitches on 300 mg are a clearance clue
Myoclonus and severe unsteadiness in someone with a low eGFR are gabapentin toxicity until proven otherwise. This is not a reason to add a second 300 mg for 'nerve pain'.
Hold. Urgent review. A level is not always available; the clinical picture plus the table is enough to stop.
Families describe 'he looks drunk on one capsule'. That is the 52-hour half-life talking.
Restart only against a new clearance and a new interval. The old 300 mg TID card is retired.
Other myoclonus causes exist. Do not diagnose from a glint. Do not climb while you wait for neurology either.
Where 300 mg sits on the clearance rows
CrCl at or above 60 mL/min: 900 to 3600 mg/day, and 300 mg three times daily is the low end.
CrCl above 30 to 59: 400 to 1400 mg/day in two divided doses. A 300 mg twice-daily plan (600 mg/day) sits in that band. 300 mg TID (900 mg) can already be high for the row.
CrCl above 15 to 29: 200 to 700 mg once daily. A single 300 mg capsule is a typical unit. Three times daily is off this row.
CrCl 15: 100 to 300 mg once daily. Below 15, reduce in proportion - 7.5 mL/min gets about half the 15 mL/min dose.
| CrCl (mL/min) | Daily range | 300 mg role |
|---|---|---|
| ≥60 | 900-3600 | 300 mg TID is the floor |
| >30-59 | 400-1400, usually BID | 300 mg BID often fits |
| >15-29 | 200-700 once daily | 300 mg once is typical |
| 15 | 100-300 once | 300 mg is the top of the row |
If the creatinine is new, the 300 mg clock is new
Do not keep a 900 mg TID card after the kidney number has moved. Ask for a rewritten interval.
Confirm with the clinician who owns the pain or epilepsy indication. This glint does not calculate your Cockcroft-Gault.
When creatinine falls, 300 mg may already be the whole day. The capsule lock stays; the interval moves. Twitches plus a low eGFR are a hold.
New ramipril, NSAIDs, or a diarrhoeal week retire last winter's TID card. Ask for a dated number before any climb past 900 mg.
Thin older bodies can hide a low clearance behind a 'normal' creatinine. Bring weight. Haemodialysis extras are not Monday bonus tablets.
AKI in hospital on a community 300 mg TID card is a common toxicity setup. Do not restart 900 mg the day you go home without a new number. Peritoneal dialysis is not the haemodialysis sticker.
A 'normal' urea after a week of vomiting is not a green light to climb past 900 mg. Re-draw. The 300 mg lock stays while the interval waits for that number.
A community pharmacist who sees a new 300 mg TID after last month's eGFR of 28 should query, not dispense on autopilot. Bring the dated number or ask them to phone the prescriber.
Sources
- Neurontin US PI Table 1 - gabapentin dose by CrCl; post-haemodialysis supplement 125-350 mg.
- Neurontin US PI 8.6 / 12.3 - half-life ~6.5 h vs ~52 h; CL/F ~190 to ~20 mL/min.
Checked against the current label and reviewed by Dr. Mira Okonkwo. See Capture → Layer → Peer-blur → Publish.