Gabapentin

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DRUGS
Gabapentin

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.

Introduction

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 

Pharamcological 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 Interactions

  • 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 in10 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

Clinic 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/day in patients with neuropathic pain. The mean visual analogue pain score decreased from 7.3 to 5.4.

References

  • eMed expert: emedexpert.com/facts/gabapentin-facts.shtml
  • Drug Bank:  drugbank.ca/drugs/DB00996
  • Medhealth.net: med-health.net/Gabapentin-Side-Effects.html
  • whatmeds.stanford.edu/medications/gabapentin.html
  • Clin Ther. 2003 Jan;25(1):81-104 (ncbi.nlm.nih.gov/pubmed/12637113)
  • J Spinal Cord Med. 2002 Summer;25(2):100-5 (ncbi.nlm.nih.gov/pubmed/12137213)
  • Wiley online library (onlinelibrary.wiley.com/doi/10.1046/j.0003-2409.2001.02399.x/full)
  • Medscape: reference.medscape.com/drug/neurontin-gralise-gabapentin-343011#0
  • Medindia: medindia.net/doctors/drug_information/gabapentin.htm
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