Gabapentin

Gabapentin, commonly known under the brand name Neurontin, is a medication used primarily to treat epilepsy and neuropathic pain. It is a first-line medication for the treatment of neuropathic pain caused by diabetic neuropathy, post-herpetic neuralgia, and central neuropathic pain. Gabapentin is also often used to help control chronic pain in adults, specifically fibromyalgia.³

The drug was first synthesised in the 1970s by researchers at Parke-Davis, a division of the American pharmaceutical company Pfizer, with the aim of creating a molecule that would mimic the chemical structure of GABA, a neurotransmitter that inhibits the excitability of neurons in the brain but would not be broken down in the body.

It was discovered that gabapentin has the ability to cross the blood-brain barrier. Although it does not bind to GABA receptors, it does bind to the α2δ (alpha-2-delta) subunit of voltage-dependent calcium channels in the central nervous system. This is believed to be the mechanism by which gabapentin exerts its analgesic effects.¹

Gabapentin’s primary use is in the management of post-herpetic neuralgia and partial seizures. Still, it is effective in other contexts as well, such as in the management of fibromyalgia and certain types of chronic pain. ³ Furthermore, it’s often used in combination with other drugs like morphine to enhance their analgesic effect.^2,7 It has also been found to have a beneficial effect on mood in patients with partial epilepsy, ^six and can even be used off-label for various psychotropic purposes.⁴

Although generally well-tolerated, gabapentin can have side effects, including drowsiness, dizziness, and loss of coordination, which can increase when combined with other medications. As with all medication, doctors need to discuss the potential risks and benefits with patients.⁵

Despite the usefulness of gabapentin in these areas, there is limited evidence for its effectiveness in the treatment of acute pain.⁸ Furthermore, while gabapentin is commonly prescribed for off-label use, there’s a need for more research into its efficacy in these areas. ⁴

Appearance

Gabapentin is commonly supplied in three forms: capsules, tablets, or as a liquid.⁵ The appearance of gabapentin varies according to the form and dosage. The capsules and tablets are usually white or yellow but can also be orange or light brown. The tablets and capsules are typically oval or capsule-shaped. Notably, the 800mg tablets are often scored and might be of a different shape. The liquid form of gabapentin is generally clear and ranges from colourless to slightly yellow. However, the exact appearance can differ according to the brand and formulation.

Tastе

Gabapentin is reported to have a bitter taste, prompting individuals to swallow capsules or tablets whole to avoid the taste.⁵ The liquid form of gabapentin is often mixed with a beverage to mask the bitter taste.

Smell

Gabapentin, in its common pharmaceutical forms (tablets, capsules, oral solutions), typically does not have a strong or distinct smell. This is because it is usually encapsulated or pressed into pill form with other inert ingredients, which don’t generally contribute a noticeable aroma.

Gabapentin is typically taken orally. It can be consumed in the form of a capsule, a tablet, or an oral solution. The intake method can be dependent on various factors, such as the condition being treated, the age of the patient, their kidney function, and overall health status. ⁹

• Minimum to feel something (mg): For the treatment of post-herpetic neuralgia or epilepsy in adults and adolescents (12 years and older), the therapy may start from 300mg on the first day. ⁵
• Low dose: On the second day of treatment, the dose might be increased to 300mg twice daily.
• Common dose: For chronic neuropathic pain, a common effective dose appears to be between 900mg and 1800mg per day, divided into three doses. ³
• High dose: The dosage can be adjusted based on response and tolerability, with a maximum dose going up to 3600mg daily.

Notes on what may happen when exceeding the high dose
Overdosing on Gabapentin can lead to symptoms such as double vision, drowsiness, slurred speech, lethargy, and diarrhoea. In severe cases, it can result in a coma.⁹

Gabapentin is primarily used to manage pain, particularly neuropathic pain, so users generally report a decrease in pain sensations when taking this medication. ³ However, gabapentin can also induce feelings of calm, relaxation, and well-being in some individuals.¹⁰ Some users may also experience drowsiness or fatigue, especially when they first start taking the drug or when the dosage is increased.⁵

The drug can cause physical effects like dizziness, drowsiness, and fatigue. More serious effects can include changes in coordination and unusual eye movements.

Gabapentin, when taken orally, typically begins to work within 2-3 hours. However, peak concentrations in plasma occur around 3-4 hours post-ingestion. This onset time can vary based on individual differences, such as metabolism rate, body mass, and state of health.

The duration of effects of gabapentin can vary depending on the dosage and the individual’s metabolism. On average, the half-life of gabapentin in the body is about 5 to 7 hours. This means it takes about 5 to 7 hours for the concentration of gabapentin in the body to reduce by half after administration. However, the actual duration of the drug’s effects can vary. For instance, the pain-relieving effects might last longer than the actual presence of the drug in the body, which can also be influenced by the nature and severity of the pain being treated.³

While gabapentin is generally well-tolerated, it does come with some risks, particularly if misused or taken in larger than recommended quantities. The NHS warns that it can cause serious problems like an allergic reaction, breathing problems, or changes in mood or behaviour. The latter can include anxiety, restlessness, or thoughts of self-harm.

In the case of an overdose, symptoms may include double vision, slurred speech, drowsiness, lethargy, and diarrhoea.¹² In severe cases, an overdose could lead to coma or death, although such instances are rare.

Gabapentin is not traditionally considered to be an addictive drug, but there have been reports of misuse and dependence, particularly among individuals with a history of substance abuse.¹⁰ This is believed to be due to the mood-enhancing effects of the drug. ⁶

Withdrawal symptoms have also been reported, suggesting that it may carry some risk of physical dependence if used regularly or in high doses. Therefore, the medication should always be taken as directed by a healthcare provider, and any changes in dosage or discontinuation should be done under medical supervision.

In the United Kingdom, gabapentin is classified as a Class C controlled substance under the Misuse of Drugs Act 1971, which means it is illegal to possess without a prescription and to supply or produce without a licence. Despite this, it’s still one of the most commonly prescribed drugs in the UK.⁵

Gabapentin can interact with other substances, and these interactions can be dangerous. For example, taking gabapentin with alcohol or other drugs that depress the central nervous system, like opioids or benzodiazepines, can increase the risk of severe drowsiness, respiratory depression, or even death.¹¹ Therefore, discussing potential interactions with a healthcare provider is important.

1. Gabapentin. (2017). PubChem. Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/Gabapentin
2. Gilron, I., Bailey, J. M., Tu, D., Holden, R. R., Jackson, A. C., & Houlden, R. L. (2005). Morphine, gabapentin, or their combination for neuropathic pain. New England Journal of Medicine, 352(13), 1324-1334. https://www.nejm.org/doi/full/10.1056/NEJMoa042580
3. Moore, R. A., Wiffen, P. J., Derry, S., & McQuay, H. J. (2011). Gabapentin for chronic neuropathic pain and fibromyalgia in adults. Cochrane Database of Systematic Reviews
   https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD007938
4. Olivier, P., Simoneau, I., Thomas, T., & Bourrel, R. (2021). Off-label Prescribing of Psychotropic Drugs by French GPs: Cross-Sectional Study. British Journal of Clinical Pharmacology.https://bpspubs.onlinelibrary.wiley.com/doi/10.1111/bcp.14747
5. NHS. (2021). Gabapentin. Retrieved from https://www.nhs.uk/medicines/gabapentin/
6. Harden, C. L., Lazar, L. M., Pick, L. H., Nikolov, B., Goldstein, M. A., Carson, D., … & Labar, D. R. (1999). A beneficial effect on mood in partial epilepsy patients treated with gabapentin. Epilepsia, 40(8), 1129-1134. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1528-1157.1999.tb00828.x
7. Eckhardt, K., Ammon, S., Hofmann, U., Riebe, A., Gugeler, N., & Mikus, G. (2000). Gabapentin enhances the analgesic effect of morphine in healthy volunteers. Anesthesia & Analgesia, 91(1), 185-191. https://journals.lww.com/anesthesia-analgesia/Fulltext/2000/07000/Gabapentin_Enhances_the_Analgesic_Effect_of.34.aspx
8. Chaparro, L. E., Wiffen, P. J., Moore, R. A., & Gilron, I. (2012). Combination pharmacotherapy for the treatment of neuropathic pain in adults. Cochrane Database of Systematic Reviews, https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD008943.pub2/full
9. National Institutes of Health. (2017). Gabapentin. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK548769/
10. Smith, R. V., Havens, J. R., & Walsh, S. L. (2016). Gabapentin misuse, abuse and diversion: a systematic review. Addiction, 111(7), 1160-1174. https://onlinelibrary.wiley.com/doi/full/10.1111/add.13324
11. FDA. (2019). FDA warns about serious breathing problems with seizure and nerve pain medicines gabapentin (Neurontin, Gralise, Horizant) and pregabalin (Lyrica, Lyrica CR). https://www.fda.gov/drugs/drug-safety-and-availability/fda-warns-about-serious-breathing-problems-seizure-and-nerve-pain-medicines-gabapentin-neurontin
12. U.S. National Library of Medicine. (2021). Gabapentin Overdose. Medline Plus. https://medlineplus.gov/ency/article/002644.htm