01
Night one is a 300 mg start
Postherpetic neuralgia is the US pain indication on Neurontin. The capsule strengths on the shelf are 100, 300, and 400 mg. Tablets at 600 and 800 mg and a 250 mg/5 mL solution exist for later math. Night one of the adult pain schedule is a single 300 mg dose. That is a start, not a verdict on whether the drug 'works.'
Day two is 300 mg twice (600 mg). Day three is 300 mg three times (900 mg). After that the labelled climb for pain can continue toward 1800 mg a day, given as 600 mg three times. Trials also tested 2400 and 3600 mg. Extra benefit above 1800 mg was not shown in those studies, while more somnolence and dizziness were.
Partial-onset seizures use a different open. From age 12 the start is already 300 mg three times a day, with room toward 600 mg three times. The longest gap between doses must stay inside 12 hours. Mixing the pain schedule and the epilepsy schedule is how people underdose a seizure and over-sedate a shingles night. Ask which indication the script was written for before you invent a third clock.
02
A week is the floor for coming off
The sentence is not optional. Reduce, discontinue, or substitute gradually over a minimum of one week. The prescriber may stretch that floor. The patient does not get to collapse it because the remaining capsules will not last the month. Status epilepticus is the labelled extreme. Agitation, insomnia, nausea, sweating, and a rebound of the original nerve pain are the everyday ones.
Postmarketing notes also describe agitation, disorientation, and confusion after a sudden stop of higher-than-recommended doses used for unapproved indications. Those symptoms eased when gabapentin was restarted. That is a reason to restart under advice and then taper, not a reason to decide the drug is 'addictive' in the opioid sense and throw the blister away.
How slow is slow enough once you are above the one-week floor is clinical judgment. Deprescribing groups often keep each cut at or under 300 mg a week and go slower after long use. Those percentages are not on the US PI. What is on the PI is the floor. A clinic letter that says 'just stop, you only take 300 mg at night' still violates that floor.
03
Sleepiness, driving, and the 2019 breathing warning
Somnolence, dizziness, and ataxia are the common tax. In epilepsy trials above age 12, at totals up to 1800 mg a day, somnolence hit 19 percent on drug versus 9 percent on placebo. Dizziness 17 versus 7. Ataxia 13 versus 6. Those three also led most dropouts. The driving line is a ban until the person has enough days on a stable dose to know whether they can judge distance and stay awake.
December 2019 brought a class-level respiratory warning. Case reports, human data, and animal work tie gabapentin to serious, life-threatening, or fatal respiratory depression when an opioid or another CNS depressant is on board, or when the lungs are already weak. If both drugs stay, start gabapentin low and watch breathing and sedation. The management of a crash can include pulling gabapentin itself.
Morphine is named in the interaction section: watch for somnolence, sedation, and a slowing respiratory rate. Hydrocodone, oxycodone, and buprenorphine sit in the same postmarketing pile. Alcohol is an unpaid member of that pile. A 300 mg capsule that felt mild alone can flatten someone who also took their usual oxycodone at 9 p.m.
04
Gralise and Horizant are not this capsule
Gralise is a once-daily gabapentin tablet taken with the evening meal and titrated on its own ladder toward 1800 mg. Horizant is gabapentin enacarbil, a prodrug with different milligrams and a restless-legs indication. Neither is interchangeable with Neurontin 300 mg capsules. A pharmacy substitution that changes the product without changing the directions is a new prescription, not a generic convenience.
DRESS (fever, rash, swollen nodes, and organ injury) and anaphylaxis or angioedema close the drug at once. Suicidal thinking is an antiepileptic-class warning: about twice the placebo risk across 199 trials, or roughly one extra case per 530 people treated for a median of 12 weeks. New mood, agitation, or talk of self-harm is a same-day call, not a note for the next pain visit.
Misuse shows up in the postmarketing file, mostly in people who already chase other substances, sometimes at higher-than-labelled totals for uses the capsule never had. The abuse potential was not measured in dedicated human studies. Evaluate that history before the first 300 mg, and watch for self-escalation. The capsule is still tapered if it has to come off. Misuse does not earn a cliff.
05
Kidneys set the ceiling before the pain score does
300 mg nerve-pain card
Creatinine clearance, not the 0-to-10 pain number, sets the legal daily range. At 60 mL/min or above, the labelled band is 900 to 3600 mg a day in three doses. Between 30 and 59, the band falls to 400 to 1400 mg, twice daily. Between 15 and 29, 200 to 700 mg once daily. At 15 mL/min, 100 to 300 mg once daily. Below 15, cut in proportion (7.5 mL/min takes half of the 15 mL/min dose).
Older adults lose filtration quietly. A 78-year-old started on 300 mg three times because 'that is the epilepsy open' can be sitting in the 30-to-59 band without anyone writing a clearance on the chart. Somnolence then gets blamed on age. The capsule was dosed for a kidney the person no longer has.
Hemodialysis adds a supplemental dose after each four-hour run, on top of a maintenance total taken from the same table. Copying a neighbour's 1800 mg pain schedule onto a dialysis week is how people arrive at the ward too sedated to stand. Ask for the clearance before asking for a higher blister.
06
The labelled climb for postherpetic pain
| Day | How the 300 mg capsule is used | Total |
|---|---|---|
| 1 | One capsule, once | 300 mg |
| 2 | One capsule, twice | 600 mg |
| 3 | One capsule, three times | 900 mg |
| Later, if needed | Two 300 mg capsules three times, or 600 mg tablets | Toward 1800 mg |
| Trials also tested | Higher totals | 2400 to 3600 mg; extra benefit above 1800 mg not shown |
Shingles pain that stays after the vesicles have crusted is the setting the 300-600-900 opening was built for. Efficacy in the two controlled postherpetic trials sat across 1800 to 3600 mg a day with similar effect through that band. The sponsor did not demonstrate that pushing past 1800 mg bought more relief. Sixteen percent of 336 people on Neurontin stopped for an adverse reaction, against 9 percent of 227 on placebo. Dizziness, somnolence, and nausea led those exits.
A person who feels nothing on night one has not failed the drug. They have taken one-sixth of a common target. A person who is already swaying on night one should not be forced to 900 mg on day three out of loyalty to a printed ladder. The ladder is a default. Kidneys, age, and other sedatives rewrite the rungs.
Food barely moves the capsule: about a 14 percent rise in AUC and Cmax. That is why 'take with dinner' is comfort, not a bioavailability trick. The real absorption story is the opposite of most drugs. As the daily milligram rises, a smaller fraction of each capsule gets in.
07
Why absorption shrinks as the capsule count rises
Gabapentin uses a saturable transporter in the gut. Bioavailability is about 60 percent at 900 mg a day, 47 percent at 1200, 34 percent at 2400, 33 percent at 3600, and 27 percent at 4800 mg, each in three divided doses. Doubling the bottle does not double the blood. That is why a jump from 1800 to 3600 mg often buys sedation without a matching drop on the pain score.
Half-life in people with ordinary kidneys is 5 to 7 hours and does not stretch just because the milligram went up. Clearance tracks creatinine clearance. Hemodialysis pulls the drug out of plasma, which is why a post-dialysis supplement exists on the renal table and why a missed session changes the next capsule.
Aluminum-magnesium antacid (the old Maalox formula in the label) cuts bioavailability by about 20 percent. Take gabapentin at least two hours after that antacid. The cation rule here is shorter than Cipro's six-hour after-gap, and it runs in one direction: after the antacid, not a symmetric sandwich. Still a clock. Still easy to miss at 11 p.m. when the heartburn chew and the 300 mg capsule land in the same handful.
08
Leave a written taper, not a leftover bottle
Write the off-ramp the day the on-ramp is agreed. Day one 300 mg, day two 600, day three 900, then a target that respects clearance. Next to that, a sentence that names the week-long floor and the person who will adjust it. A leftover bottle with no plan is how people stop on a Friday because the pain 'felt better.'
Opioids, other sedatives, and a low creatinine clearance belong on the same scrap of paper. Those three change whether 300 mg is gentle or enough to flatten breathing. The 2019 warning is a monitoring order, not a rumor from a forum.
Bring the written card to the visit that started the script. The gabapentin profile keeps the full renal table, the seizure schedule, and the interaction list. This dispatch is the two-move version: climb on a labelled clock, leave on a labelled taper. Nothing in the middle is a one-step drop.