Gabapentin

Gabapentin (中文: 加巴噴丁) is an anticonvulsant medication used primarily in the treatment of:

• Focal seizures with or without secondary generalization.
• Neuropathic pain caused caused by diabetic neuropathy, postherpetic neuralgia and central neuropathic pain.
• Migraine prophylaxis

Drug Names

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

Pronunciation

Gabapentin 100mg

Gabapentin 300mg

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.

Drug Management

Monitoring

• Recognize signs of blood, liver, or skin toxicity. Seek immediate medical attention if symptoms such as fever, sore throat, rash, blistering, mouth ulcers, bruising or bleeding develop.
• Patients with heart failure should be weighed regularly to detect fluid retention.
• Patients with pre-existing cardiac conduction disorders should be carefully monitored.
• changes in mood, the development or worsening depression, and/or any thoughts or behaviour of suicide.

Drug interaction

Drugs given with gabapentin	Potential Effect
Antacids (containing Magnesium with aluminium)	Absorption of gabapentin from the gut is reduced by antacids. It is recommended that gabapentin is taken at least 2 hours after any such antacid.
Morphine	Morphine reduces the clearance of gabapentin; patients receiving both drugs should be monitored for signs for CNS depression and doses should be reduced accordingly.

Caution

• Avoid abrupt withdrawal
• Used with caution in patients with renal impairment and in those undergoing haemodialysis
• History of psychotic illness

Renal impairment

Reduced doses are recommended for patients with renal impairment or those undergoing haemodyalysis:

• If creatinine clearance 50 to 79 ml/minute: 600 to 1800 mg daily in 3 divided doses.
• If creatinine clearance 30 to 49 ml/minute: 300 to 900 mg daily in 3 divided doses.
• If creatinine clearance 15 to 29 ml/minute: 300 mg on alternate days to 600 mg daily in 3 divided doses.
• If creatinine clearance less than 15 ml/minute: 300 mg on alternate days to 300 mg daily in 3 divided doses.

For those undergoing haemodialysis: the recommended loading dose is 300 mg to 400 mg followed by 200 to 300 mg after each 4 hours of haemodialysis. On dialysis-free days no doses of gabapentin should be given.

Pregnancy

Women of child-bearing potential should discuss with a specialist the impact of both epilepsy, and its treatment, on the outcome of pregnancy. There is an increased risk of teratogenicity associated with the use of antiepileptic drug (especially if used during the first trimester)

Breast-feeding

Use during breast feeding is not recommended.

Epilepsy and driving

Driving by patients with epilepsy is generally regulated. Also, antiepileptic drugs may produce CNS-related adverse effects, including dizziness and drowsiness, that could impair a patient’s ability to drive a vehicle or operate machinery, particularly during the initial stages of therapy.

FAQ

How should I take the tablet?

Take preferably with or after food.

What should I avoid while taking?

Avoid abruptly discontinue the medication.

What happen if I overdose?

Contact your primary care doctor. If emergency situation, call 999

What happen if I miss a dose?

Take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.