Gabapentin (US brand name Neurontin® and generic) is an analgesic and antiepileptic drug structurally related to gamma-aminobutyric acid (GABA), the key inhibitory neurotransmitter in the cerebral cortex. Here is basic information about this medication.
Mechanism of action
The mechanism of action of gabapentin is complex and not clearly known. It does not act on GABA receptors or affect the reuptake of GABA. The main mechanism of action is probably that it binds to calcium channels and modulates the influx of calcium. Through this, it reduces the release of excitatory neurotransmitters like glutamate. In addition, through indirect effects, it increases the levels of GABA in the brain.
Gabapentin is somewhat unique; it does not bind to plasma proteins, is not metabolized in the liver, and is excreted unchanged in the urine. This is why its levels are sensitive to impairments in renal function.
Note: Gabapentin is not approved by the FDA for any psychiatric indication. It is discussed on this website (and in standard psychiatry textbooks) because it is sometimes used off-label by mental health clinicians.
1. Postherpetic neuralgia in adults
2. Adjunctive therapy in the treatment of partial onset seizures, with and without secondary generalization, in adults and pediatric patients 3 years and older with epilepsy
A. Postherpetic neuralgia
Initial: On day 1, single 300 mg dose
On day 2, 300 mg two times a day (600 mg/day)
On day 3, 300 mg three times a day (900 mg/day)
Titrate: Up to 600 mg three times daily (1800 mg/day)
Maximum: 1800 mg/day (600 mg three times daily). The additional benefit of using doses greater than 1800 mg/day was not demonstrated.
B. Epilepsy with Partial Onset Seizures
1. Patients 12 years of age and older
Initial: 300 mg three times a day
Titrate: May be titrated upwards to recommended maintenance dose of 300-600 mg three times a day
Maximum: Up to 2400 mg/kg/day have been well tolerated in long term clinical studies
2. Pediatric patients 3 to 11 years of age
Initial: 10-15 mg/kg/day in three divided doses
Titrate: Over a period of approximately 3 days to reach the required maintenance dose
a. Age 3 to 4 years: 40 mg/kg/day, given in three divided doses
b. Age 5 to 11 years: 25 to 35 mg/kg/day, given in three divided doses
Maximum: Up to 50 mg/kg/day have been well tolerated in long term clinical studies
The maximum time interval between doses should not exceed 12 hours.
1. Patients 12 years of age and older with Renal Impairment
Creatinine Clearance ≥60 mL/min: 900 to 3600 mg/day in three divided doses
Creatinine Clearance 30-59 mL/min: 400 to 1400 mg/day in three divided doses
Creatinine Clearance 15-29 mL/min: 200 to 700 mg/day in three divided doses
Creatinine Clearance <15mL/min: 100 to 300 mg/day in three divided doses
Depending on the maintenance dose regimen, patients on hemodialysis should receive supplemental (in addition to maintenance) post-hemodialysis dose ranging from 125 to 350 mg after each 4 hours of hemodialysis (refer to details in the prescribing information, link provided below).
Adjust the dose based upon creatinine clearance values
1. May be administered with or without food
2. Capsules should be swallowed whole with water
3. Patients should be instructed that if they choose to divide the scored 600 mg or 800 mg tablet in order to administer half tablet, the other half should be taken with the next dose. Half-tablets not used within 28 days of dividing the scored tablet should be discarded.
4. If gabapentin is reduced, discontinued, or substituted with an alternative medication, it should be done gradually over a minimum of 1 week
Dosage forms and strengths
Capsules: 100 mg, 300 mg, and 400 mg
Tablets: 600 mg (scored) and 800 mg (scored). Generics tablets also available in 100, 300, and 400 mg strengths
Oral solution: 250 mg/5mL
Please refer to Prescribing Information (see link below) for a complete discussion of dosage, administration, warnings and precautions, contraindications, etc.
Copyright 2016, Rajnish Mago, MD. All rights reserved. May not be reproduced in any form without express written permission.
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