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Drugs reference index «Gabapentin»

Gabapentin

Pronunciation: (GAB-a-PEN-tin)Class: Anticonvulsant

Trade Names:Neurontin- Tablets 600 mg- Tablets 800 mg- Capsules 100 mg- Capsules 300 mg- Capsules 400 mg- Oral solution 250 mg per 5 mL

Apo-Gabapentin (Canada)CO Gabapentin (Canada)Gen-Gabapentin (Canada)Novo-Gabapentin (Canada)PMS-Gabapentin (Canada)ratio-Gabapentin (Canada)

Pharmacology

Mechanism unknown; structurally related to GABA, but does not react with GABA receptors.

Pharmacokinetics

Absorption

Bioavailability decreases as dose increases: bioavailability is approximately 60%, 47%, 34%, 33%, and 27% following 900, 1,200, 2,400, 3,600, and 4,800 mg/day given in 3 divided doses, respectively. Food has only a slight effect on rate and extent of absorption (14% increase in AUC and C max ).

Distribution

Less than 3% bound to plasma proteins. Vd is approximately 58 L.

Metabolism

Not significantly metabolized in humans.

Elimination

Excreted unchanged in urine. Half-life is 5 to 7 h.

Special Populations

Renal Function Impairment

In CrCl less than 30 mL/min, half-life is approximately 52 h.

Hepatic Function Impairment

Studies have not been performed.

Elderly

Renal Cl decreases as a result of age-related decline in renal function.

Children

Children between 1 mo and younger than 5 yr of age achieved approximately 30% lower exposure (AUC) than that observed in those 5 yr of age and older. Gabapentin elimination half-life averaged 4.7 h and was similar across the age groups studied. Higher oral Cl values were observed in children younger than 5 yr of age compared with those observed in children 5 yr of age and older, when normalized per body weight. The Cl was highly variable in infants younger than 1 yr of age.

Hemodialysis

The half-life is approximately 132 h on nondialysis days; during dialysis, half-life is reduced to 3.8 h. Gabapentin is significantly removed by hemodialysis.

Indications and Usage

Adjunctive therapy in treatment of partial seizures with or without secondary generalization in patients older than 12 yr of age with epilepsy; adjunctive therapy for partial seizures in children 3 to 12 yr of age; management of postherpetic neuralgia in adults.

Unlabeled Uses

Agitation in dementia; alcohol withdrawal; bipolar disorder; cocaine withdrawal; diabetic neuropathy; fibromyalgia; headaches; hiccups (singultus); hot flashes (cancer- and/or postmenopausal-related); hyperhidrosis; nausea (cancer-related); neuralgia/neuropathy/chronic pain; prevention of migraine; pruritus (brachioradial/cholestatic/uremic); rectal administration; restless leg syndrome; tremors in multiple sclerosis.

Contraindications

Standard considerations.

Dosage and Administration

EpilepsyAdults and Children older than 12 yr of age

PO 300 mg 3 times daily initially. May increase as necessary to 900 to 1,800 mg/day (divided 3 times daily).

Children 5 to 12 yr of age

PO Initiate therapy at 10 to 15 mg/kg/day in 3 divided doses and titrate dose upward over a period of approximately 3 days to effective dose. Effective dose is 25 to 35 mg/kg/day in 3 divided doses.

Children 3 to 4 yr of age

PO Initiate therapy at 10 to 15 mg/kg/day in 3 divided doses and titrate dose upward over a period of approximately 3 days to effective dose. Effective dosage is 40 mg/kg/day in 3 divided doses.

Postherpetic NeuralgiaAdults

PO Start with a single 300 mg dose on day 1, 600 mg on day 2 (divided twice daily), and 900 mg on day 3 (divided 3 times daily). Subsequently, titrate the dose upward as needed for pain relief to a daily dose of 1,800 mg (divided 3 times daily).

Dosage Adjustment for Renal Function ImpairmentAdults and Children older than 12 yr of age CrCl 60 mL/min or higher

Total daily dose range 900 to 3,600 mg/day.

CrCl 30 to 59 mL/min

Total daily dose range 400 to 1,400 mg/day.

CrCl 16 to 29 mL/min

Total daily dose range 200 to 700 mg/day.

CrCl 15 mL/min

Total daily dose range 100 to 300 mg/day.

CrCl less than 15 mL/min

Reduce dose in proportion to CrCl (eg, patients with CrCl 7.5 mL/min should receive half the daily dose of patients with CrCl 15 mL/min).

Patients on hemodialysis

Maintenance doses based on CrCl as recommended, plus a supplemental posthemodialysis dose administered after each 4 h of hemodialysis as follows: If maintenance dose is 100 mg daily, postdialysis dose is 125 mg; if maintenance dose is 125 mg daily, postdialysis dose is 150 mg; if maintenance dose is 150 mg daily, postdialysis dose is 200 mg; if maintenance dose is 200 mg daily, postdialysis dose is 250 mg; if maintenance dose is 300 mg daily, postdialysis dose is 350 mg.

General Advice

  • Tablets, capsules, and oral solution are interchangeable on a mg-to-mg basis.
  • Max time between doses in 3-times-daily schedule should not exceed 12 h.
  • Administer without regard to meals. Administer with food if GI upset occurs.
  • If 600 or 800 mg scored tablet is split to administer a half-tablet, administer unused half-tablet at next dose. Discard any half-tablet not used within several days of splitting.
  • Measure and administer prescribed dose of oral solution using dosing syringe, dosing spoon, or dosing cup.
  • Reduce dose gradually over a minimum of 1 wk if gabapentin is discontinued.

Storage/Stability

Store tablets and capsules at 59° to 86°F. Store oral solution at 36° to 46°F.

Drug Interactions

Antacids

May reduce bioavailability of gabapentin. Gabapentin should be taken 2 h after antacid.

Cimetidine

Renal Cl of gabapentin may be reduced slightly. This interaction is not expected to be clinically important.

Hormonal contraceptives

Norethindrone plasma levels may be increased 13%, which is not expected to be clinically important.

Hydrocodone

The AUC of gabapentin may be increased by 14% while the hydrocodone C max and AUC are decreased by gabapentin in a dose-dependent manner. Observe the clinical response of the patient when starting, stopping, or changing the gabapentin dose. If an interaction is suspected, adjust the hydrocodone dose as needed.

Morphine

The AUC of gabapentin may be increased by morphine. The magnitude of this interaction at various gabapentin doses has not been evaluated. Observe the clinical response of the patient when starting, stopping, or changing the gabapentin dose. If an interaction is suspected, adjust the gabapentin dose as needed.

Naproxen

In lower than therapeutic doses, gabapentin absorption was increased 12% to 15% by naproxen. The magnitude of this interaction within the recommended dose ranges of either drug is not known. Observe the clinical response of the patient when starting, stopping, or changing the dose of either drug. If an interaction is suspected, adjust the gabapentin dose as needed.

Laboratory Test Interactions

False-positive readings for Ames N-Multistix SG dipstick test when gabapentin is added to other antiepileptic drugs. Sulfosalicylic acid precipitation procedure is recommended to determine the presence of urine protein.

Adverse Reactions

Cardiovascular

Hypertension (at least 1%); vasodilation (1%);

CNS

Dizziness (28%); somnolence (21%); ataxia (13%); fatigue (11%); hostility, nystagmus (8%); tremor (7%); asthenia (6%); emotional lability (4%); abnormal thinking, headache, hyperkinesia (3%); abnormal gait, amnesia, depression, dysarthria, incoordination, nervousness (2%); anxiety, confusion, malaise, paresthesia, vertigo (at least 1%); abnormal coordination, hypesthesia, twitching (1%); aura disappeared, occipital neuralgia, sleepwalking; movement disorder (postmarketing).

Dermatologic

Abrasion, pruritus, rash (1%); erythema multiforme, Stevens-Johnson syndrome (postmarketing).

EENT

Diplopia (6%); amblyopia, rhinitis (4%); pharyngitis (3%); abnormal vision (at least 1%); conjunctivitis, otitis media (1%).

GI

Nausea/vomiting (8%); diarrhea (6%); dry mouth (5%); constipation (4%); abdominal pain (3%); dental abnormalities, dry mouth or throat, dyspepsia, flatulence (2%); anorexia, gingivitis (at least 1%); increased appetite (1%).

Genitourinary

Impotence (2%); breast hypertrophy (postmarketing).

Hematologic-Lymphatic

Purpura (at least 1%); decreased WBC, leukopenia (1%); coagulation defect.

Hepatic

Hepatitis; elevated LFTs, jaundice (postmarketing).

Metabolic-Nutritional

Peripheral edema (8%); weight gain (3%); hyperglycemia (1%); dehydration; blood glucose fluctuations, hyponatremia (postmarketing).

Musculoskeletal

Back pain, myalgia (2%); arthralgia, decreased or absent reflexes, increased reflexes (at least 1%); fracture (1%).

Respiratory

Bronchitis, respiratory infection (3%); coughing (2%); pneumonia (at least 1%); hoarseness, pseudocroup.

Miscellaneous

Viral infection (11%); fever (10%); infection (5%); accidental injury (3%); face edema (at least 1%); infectious mononucleosis; angioedema (postmarketing).

Precautions

Monitor

Monitor patients for clinical worsening, suicidality, and unusual changes in behavior, especially during the first few months of therapy or at times of dose changes (either increases or decreases), and during discontinuation of therapy.

Pregnancy

Category C .

Lactation

Excreted into breast milk.

Children

Effectiveness as adjunctive therapy in the treatment of partial seizures in children younger than 3 yr of age not established; safety and efficacy in management of postherpetic neuralgia in children not established.

Elderly

Because of age-related renal impairment, adjust dose based on CrCl.

Renal Function

Adjust dose based on CrCl.

Carcinogenesis

May have carcinogenic potential.

Hazardous Tasks

May cause dizziness, drowsiness, and other symptoms of CNS depression.

Neuropsychiatric effects

Emotional lability, hostility, thought disorders, and hyperkinesia have been reported with increased frequency in patients 3 to 12 yr of age with epilepsy.

Serious adverse reactions

During clinical trials, some patients experienced status epilepticus, and 8 sudden, unexplained deaths occurred. The association of these reactions with gabapentin use is unclear.

Suicidal ideation

Increased risk of suicidal thinking and behavior in patients taking antiepileptic drugs for any indication.

Withdrawal

Do not discontinue antiepileptic drugs abruptly because of possible increased seizure frequency from drug withdrawal.

Overdosage

Symptoms

Diarrhea, double vision, drowsiness, lethargy, slurred speech.

Patient Information

  • Advise patient or caregiver to read the patient information leaflet before starting therapy and with each refill.
  • Counsel patient, family, or caregiver that antiepileptic drugs may increase the risk of suicidal thoughts and behavior and to be alert for the emergence or worsening of symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm, and to immediately report any of these symptoms to health care provider.
  • Instruct patient with epilepsy to continue to take other medications for seizures unless advised otherwise by health care provider.
  • Advise patient or caregiver that medication will be started at a low dose and then increased as tolerated until maximum benefit has been obtained.
  • Instruct patient or caregiver to take exactly as prescribed and not to change the dose or discontinue therapy unless advised by health care provider.
  • Advise patient or caregiver to take without regard to meals but to take with food if stomach upset occurs.
  • Advise patient or caregiver that maximum time between doses in 3-times-daily schedule should not exceed 12 h.
  • Advise patient or caregiver that, if they split the 600 or 800 mg scored tablet to administer a half-tablet dose, they should take the unused half-tablet at the next dose. Half-tablets not used within several days of splitting should be discarded.
  • Advise patient or caregiver using oral solution to measure and administer prescribed dose using dosing syringe, spoon, or cup.
  • Advise patient or caregiver that if medication needs to be discontinued, it will be slowly withdrawn over a period of 1 wk or more unless safety concerns (eg, rash) require a more rapid withdrawal.
  • Caution patient that drug may cause dizziness, drowsiness, or incoordination, and to use caution while driving or performing other tasks requiring mental alertness or coordination until tolerance is determined.
  • Instruct patient or caregiver to contact health care provider if seizures worsen or if new types of seizures occur.
  • Advise patient or caregiver to inform health care provider if any of the following occur: emotional lability, hostility, thought disorders or abnormal thinking, restlessness or hyperactivity, excessive dizziness or drowsiness, swelling in feet or ankles, any unexplained symptom or feeling.
  • Advise patient with epilepsy to carry medical identification (eg, card, bracelet) indicating medication usage and epilepsy.
  • Advise pregnant patients taking gabapentin to enroll in the North American Antiepileptic Drug Pregnancy Registry. This can be done by calling 1-888-233-2334.

Copyright © 2009 Wolters Kluwer Health.

  • Gabapentin Prescribing Information (FDA)
  • Gabapentin MedFacts Consumer Leaflet (Wolters Kluwer)
  • Gabapentin Detailed Consumer Information (PDR)
  • gabapentin Advanced Consumer (Micromedex) - Includes Dosage Information
  • Neurontin Prescribing Information (FDA)
  • Neurontin MedFacts Consumer Leaflet (Wolters Kluwer)
  • Neurontin Consumer Overview

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