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Gabapentin

Drug Reference 9 min 1797

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Created On: 27/09/2019

Gabapentin is an anti-epileptic medication which is also known an anticonvulsant.

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Introduction

Gabapentin is an anti-epileptic medication which is also known an anticonvulsant. It affects the chemicals and nerves in the body responsible for causing seizures and some types of pain. Gabapentin may also be used to treat other nerve painful conditions (such as diabetic neuropathy, peripheral neuropathy, trigeminal neuralgia) and restless legs syndrome.

Pharmacological Class: Anti-epileptic & Anti-convulsant

Indications

Fibromyalgia
Postoperative analgesic
Migraine prophylaxis
Headache
Painful diabetic neuropathy
Depression
Essential tremor
Generalized tonic-clonic seizures
Insomnia
Posttraumatic stress disorder (PTSD)
Irritable bowel syndrome (IBS)
Trigeminal neuralgia
Alcohol dependence
Refractory chronic cough

Pharmachologic action

Gabapentin interacts with cortical neurons at auxiliary subunits of voltage-sensitive calcium channels. It increases the synaptic concentration of gamma-aminobutyric acid (GABA), enhances GABA responses at non-synaptic sites in neuronal tissues and reduces the release of mono-amine neurotransmitters. It has been found that antihyperalgesic and antiallodynic effects of gabapentin are mediated by descending noradrenergic system, resulting in the activation of spinal alpha 2-adrenergic receptors. Gabapentin has also been shown to bind and activate adenosine A1 receptors.

Dosage

Adult dose for

Epilepsy: 300 mg orally, 3 times a day
Post herpetic neuralgia: 300 mg orally, once a day (evening)
Restless leg syndrome: 600 mg orally, once a day
Diabetic neuropathy: 900 mg orally, once a day

Pediatric dose

Pain: 10-15 mg/kg/day orally, divided into 3 equal doses

Pharmacokinetics

Gabapentin is rapidly absorbed by the L-amino acid transport system, which is a carrier-mediated, saturable transport system. The volume of distribution is found to be 58±6 L and plasma protein binding is less than 3%. The plasma half life is 5-7 hours.

Contraindications

In patients with:

Hypersensitivity
Kidney disease
Heart disease
Liver disease

Drug interaction

Reduces effects of Neurontin, when administrated with antacids
Frequent use of alcohol may seriously reduce Neurontin effectiveness
It may increase blood levels, when administrated with Tagamet (cimetidine)
It may led to phenytoin toxicity, when administrated with dilantin

Side effects

Common side effects (affecting between 1 in 10 to 1 in 100)

Sleepiness
Fatigue
Visual changes, including double vision
Tremor
Runny nose
Weight gain
Indigestion or nausea
Nervousness
Muscle ache
Dry mouth or sore throat
Headache
Unusual thoughts
Memory loss
Diarrhea or constipation
Swelling of hands or feet
Fever
Itchy eyes

Uncommon side effects (affecting 1 in 100 to 1 in 1000)

Sinus
Chest pain
Cough
Shortness of breath
Sore throat

Rare side effects (affecting less than 1 in 10,000)

Blistering
Peeling of skin
Swelling of limbs

Precautions

Caution should be taken in patients with depression, suicidal thoughts, kidney impairment, allergy, children especially less than 3 years, pregnancy and breastfeeding
Driving and operating machinery should not be done as, it causes drowsiness, dizziness, or blurred vision
It can affect blood sugar level, thus sugar levels should be monitored regularly
Patient may develop increased risk of suicidal thoughts, watch them carefully

Clinical evidence

Data from 5 randomized, placebo-controlled trials were included in the review, 1 of which has not yet been published. Gabapentin has been found to be effective in treating painful diabetic neuropathy, postherpetic neuralgia and other neuropathic pain syndromes. Based on available data, 1800 mg/d is recommended for greater efficacy. At doses of 1800 to 3600 mg/d, gabapentin was effective and well tolerated in the treatment of adults with neuropathic pain.
Seven subjects with neuropathic pain, who were more than 30 days post spinal cord injury (SCI), completed the study. Two groups received a 4-week course of gabapentin and placebo in a randomized crossover design with a 2-week washout period. Data were analyzed using Wilcox on signed rank test. Gabapentin has some beneficial effects on certain types of neuropathic pain. There was a significant decrease of "unpleasant feeling" and in both "pain intensity" and "burning sensation" at the fourth week of gabapentin than placebo.
In a study of 122 chronic pain patients [97 with neuropathic pain (postherpetic neuralgia, diabetic neuropathy, sympathetically maintained pain and phantom pain)] treated with gabapentin for at least 30 days, showed a statistically significant (p␣< 0.0001) reduction in pain scores on a median dose of 1200 mg/dayin patients with neuropathic pain. The mean visual analogue pain score decreased from 7.3 to 5.4.