Gabapentin

Catergory: Anticonvulsant medication

Pronunciation

Gabapentin 100mg

Gabapentin 300mg

Generic Name 藥名	HA Code 藥物代碼	Classification藥物分類
Gabapentin Capsule 100mg	GABA01	P1S1S3

Mechanism of Action

Anticonvulsant medication. It inhibits the alpha 2-delta subunit of voltage-gated calcium channels.

Dosage

Epilepsy	By mouth: the initial oral dose is 300 mg on day 1, then 300mg twice daily on day 2, then 300mg 3 times daily on day 3. Alternatively, 300 mg three times daily on day 1; then increased according to response in steps of 300 mg every 2 -3 days. Usual dose: 0.9 – 3.6 g daily in 3 divided doses (Max. 4.8 g daily) Doses in children, for use as adjunctive therapy in children aged 6 years and over, and as monotherapy in those aged 12 years or over. 6-12 years (adjunctive therapy): initially 10 mg/kg (max. 300 mg) once daily on day 1, then 10 mg /kg (max. 300mg) twice daily on day 2, then 10mg mg/kg (max. 300 mg) 3 times daily on day 3; Usual dose 25 – 35 mg/kg daily in 3 divided doses; Max. 70 mg/kg daily in 3 divided doses.
Neuropathic Pain	By mouth: 300 mg once daily on day 1, then 300 mg twice daily on day 2, then 300 mg 3 times daily on day 3. Alternatively, 300 mg 3 times daily on day 1, then increased according to response in steps of 300mg (in 3 divided doses) every 2-3 days up to max. 3.6 g daily.
Migraine prophylaxis	By mouth: initially 300 mg daily, increased according to response up to 2.4 g daily in divided doses.

As with other antiepileptics, withdrawal of gabapentin therapy or transition to or from another type of antiepileptic therapy should be made gradually to avoid precipitating an increase in seizure frequency. Withdrawal symptoms typically emerge within 12 hours to 7 days after stopping gabapentin. Commonly reported symptoms include agitation, confusion, disorientation, upset stomach and sweating. In some cases, patients experienced delirium and withdrawal seizures, which may only respond to the re-administration of gabapentin.

Side Effects

Common side effects include:

• Dizziness, fatigue, drowsiness, ataxia, peripheral edema (swelling of extremities), nystagmus and tremor.
• May produce sexual dysfunction in some patients

Potentially serious side effects include:

• An increased risk of suicide, aggressive behaviour
• Acute renal failure
• Deranged liver function tests, hepatitis, jaundice

Rarely, pancreatitis, Stevens-Johnson syndrome and blood glucose functions in diabetes, dystonia, palpitations, thrombocytopenia and tinnitus have been reported. An antiepileptic hypersensitivity syndrome, comprising fever, rash, myocarditis, or myositis. Overdosage of gabapentin, particularly in combination with other CNS depressants, may result in coma.

Pharmacokinetics

Oral bioavailability	Gabapentin is absorbed from the intestines by means of an active transport process which is saturable, so the pharmacokinetics of gabapentin are dose-dependent, with diminished bioavailability and delayed peak levels at higher doses. Food increases the bioavailability by about 10%.	Onset of action	Gabapentin at a low dose of 100 mg has a Tmax (time to peak levels) of about 1.7 hours, while the Tmax increases to 3 to 4 hours at higher doses.	Metabolism	Gabapentin undergoes little or no metabolism.	Elimination half-life	Gabapentin is eliminated renally in the urine. The elimination half-life has been reported to be about 5 to 7 hours. Gabapentin is distributed into breast milk.