Indications
Partial seizures (adjunct treatment) (immediate-release
only). Postherpetic neuralgia. Restless legs syndrome
(Horizant only). Unlabeled Use: Neuropathic
pain. Prevention of migraine headache. Bipolar
disorder. Anxiety. Diabetic peripheral neuropathy.
Action
Mechanism of action is not known. May affect transport
of amino acids across and stabilize neuronal membranes.
Therapeutic Effects: Decreased incidence
of seizures. Decreased postherpetic pain. Decreased leg
restlessness.
Pharmacokinetics
Absorption: Well absorbed after oral administration
by active transport. At larger doses, transport becomes
saturated and absorptionp(bioavailability ranges from
60% for a 300-mg dose to 35% for a 1600-mg dose).
Distribution: Crosses blood-brain barrier; enters
breast milk.
Metabolism and Excretion: Eliminated mostly by
renal excretion of unchanged drug.
Half-life: Adults—5–7 hr (normal renal function);
up to 132 hr in anuria; Children—4.7 hr.
TIME/ACTION PROFILE (blood levels)
ROUTE ONSET PEAK DURATION
PO-IR rapid 2–4 hr 8 hr
PO-SR unknown 5–8 hr 24 hr
Contraindications/Precautions
Contraindicated in: Hypersensitivity.
Use Cautiously in: All patients (mayqrisk of suicidal
thoughts/behaviors); Renal insufficiency (pdose
and/orqdosing interval if CCr 60 mL/min); OB: Pregnancy;
Pedi: Children 18 yr (sustained-/extended-release)
or 3 yr (immediate-release) (safety not established);
Lactation: Discontinue drug or bottle-feed;
Geri: May be more susceptible to toxicity due to age-relatedpin
renal function.
Adverse Reactions/Side Effects
CNS: SUICIDAL THOUGHTS, confusion, depression, dizziness,
drowsiness, sedation, anxiety, concentration difficulties
(children), emotional lability (children), hostility,
hyperkinesia (children), malaise, vertigo,
weakness. EENT: abnormal vision, nystagmus. CV:
hypertension. GI: weight gain, anorexia, flatulence,
gingivitis. MS: RHABDOMYOLYSIS, arthralgia,qcreatine
kinase. Neuro: ataxia, altered reflexes, hyperkinesia,
paresthesia. Misc: ANAPHYLAXIS, ANGIOEDEMA, MULTIORGAN
HYPERSENSITIVITY REACTIONS.
Interactions
Drug-Drug: Antacids maypabsorption of gabapentin.
qrisk of CNS depression with other CNS depressants,
including alcohol, antihistamines, opioids,
and sedative/hypnotics. Mayphydrocodone levels.
Drug-Natural Products: Kava-kava, valerian,
or chamomile canqCNS depression.
Route/Dosage
The sustained-/extended-release formulations should
not be interchanged with the immediate-release products.
Epilepsy
PO (Adults and Children 12 yr): 300 mg 3 times
daily initially. Titration may be continued until desired
(range is 900–1800 mg/day in 3 divided doses; doses
should not be more than 12 hr apart). Doses up to
2400–3600 mg/day have been well tolerated.
PO (Children 5–12 yr): 10–15 mg/kg/day in 3 divided
doses initially titrated upward over 3 days to 25–
35 mg/kg/day in 3 divided doses; dosage interval
should not exceed 12 hr (doses up to 50 mg/kg/day
have been used).
PO (Children 3–4 yrs): 10–15 mg/kg/day in 3 divided
doses initially titrated upward over 3 days to 40
mg/kg/day in 3 divided doses; dosage interval should
not exceed 12 hr (doses up to 50 mg/kg/day have been
used).
Renal Impairment
PO (Adults and Children 12 yr): CCr 30–59 mL/
min—200–700 mg twice daily; CCr 15–29 mL/
min—200–700 mg once daily; CCr 15 mL/min—
100–300 mg once daily; CCr 15 mL/min—Reduce
daily dose in proportion to CCr.
Postherpetic Neuralgia
PO (Adults): Immediate-release—300 mg once
daily on first day, then 300 mg 2 times daily on second
day, then 300 mg 3 times/day on day 3, may then be titrated
upward as needed up to 600 mg 3 times/day;
Sustained-release (Gralise)—300 mg once daily on
first day, then 600 mg once daily on second day, then
900 mg once daily on days 3–6, then 1200 mg once
daily on days 7–10, then 1500 mg once daily on days
11–14, then 1800 mg once daily thereafter; Extendedrelease
(Horizant)—600 mg once daily in the morning
on days 1–3, then 600 mg twice daily thereafter.
Renal Impairment
PO (Adults): CCr 30–59 mL/min—200–700 mg
twice daily (immediate-release); 600–1800 mg once daily (sustained-release [Gralise]); 300 mg once daily
in the morning on days 1–3, then 300 mg twice daily
thereafter (mayqto 600 mg twice daily, as needed)
(extended-release [Horizant]); CCr 15–29 mL/
min—200–700 mg once daily (immediate-release);
sustained release (Gralise) not recommended; 300 mg
in the morning on days 1 and 3, then 300 mg once daily
in the morning thereafter (mayqto 300 mg twice daily,
as needed) (extended-release [Horizant]); CCr 15 mL/
min—100–300 mg once daily (immediate-release);
sustained release (Gralise) not recommended; CCr
15 mL/min—pdaily dose in proportion to CCr (immediate
release); sustained release (Gralise) not recommended;
300 mg every other day in the morning
(mayqto 300 mg once daily in the morning, as
needed) (extended-release [Horizant]); CCr 15 mL/
min (on hemodialysis)—300 mg after each dialysis
session (mayqto 600 mg after each dialysis session, as
needed) (extended-release [Horizant]).
Restless Legs Syndrome
PO (Adults): Extended-release (Horizant)—600
mg once daily at 5 PM.
Renal Impairment
(Adults): CCr 30–59 mL/min—300 mg once daily at
5 PM; mayqto 600 mg once daily at 5 PM as needed;
CCr 15–29 mL/min—300 mg once daily at 5 PM; CCr
15 mL/min—300 mg every other day; CCr 15 mL/
min (on hemodialysis)—Not recommended.
Neuropathic Pain (unlabeled use)
PO (Adults): 100 mg 3 times daily initially. Titrate
weekly by 300 mg/day up to 900–2400 mg/day (maximum:
3600 mg/day).
PO (Children): 5 mg/kg/dose at bedtime initially then
qto 5 mg/kg twice daily on day 2 and 5 mg/kg 3 times
daily on day 3. Titrate to effect up to 8–35 mg/kg/day
in 3 divided doses.
Availability (generic available)
Capsules: 100 mg, 300 mg, 400 mg. Cost: Generic—
100 mg $11.45/100, 300 mg $15.18/100, 400 mg
$12.36/100. Tablets: 600 mg, 800 mg. Cost: Generic—
600 mg $33.96/100, 800 mg $49.20/100. Extended-
release tablets (Horizant): 300 mg, 600
mg. Sustained-release tablets (Gralise): 300 mg,
600 mg. Cost: 300 mg $99.00/30, 600 mg $329.40/90.
Oral solution (cool strawberry anise flavor): 250
mg/5 mL. Cost: Generic—$148.91/470 mL.
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