Gabapentin

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Gabapentin, sold under the brand name Neurontin among others, is an anticonvulsant medication primarily used to treat neuropathic pain and also for partial seizures<ref name="NICE"/><ref name="Neurontin label" /> of epilepsy. It is a commonly used medication for the treatment of neuropathic pain caused by diabetic neuropathy, postherpetic neuralgia, and central pain.<ref name=Attal2010>Template:Cite journal</ref> It is moderately effective: about 30–40% of those given gabapentin for diabetic neuropathy or postherpetic neuralgia have a meaningful benefit.<ref name=Wiffen2017 />

Gabapentin, like other gabapentinoid drugs, acts by decreasing activity of the α₂δ-1 protein, coded by the CACNA2D1 gene, first known as an auxiliary subunit of voltage gated calcium channels.<ref name="pmid32521436" /><ref name="pmid23642658" /><ref name="pmid32321743" /> However, see Pharmacodynamics, below. By binding to α₂δ-1, gabapentin reduces the release of excitatory neurotransmitters (primarily glutamate) and as a result, reduces excess excitation of neuronal networks in the spinal cord and brain. Sleepiness and dizziness are the most common side effects. Serious side effects include respiratory depression, and allergic reactions.<ref name="Neurontin label" /> As with all other antiepileptic drugs approved by the FDA, gabapentin is labeled for an increased risk of suicide. Lower doses are recommended in those with kidney disease.<ref name="Neurontin label" />

Gabapentin was first approved for use in the United Kingdom in 1993.<ref>Template:Cite book</ref> It has been available as a generic medication in the United States since 2004.<ref name="Reed2012"/> It is the first of several other drugs that are similar in structure and mechanism, called gabapentinoids. In 2022, it was the tenth most commonly prescribed medication in the United States, with more than 40Template:Nbspmillion prescriptions.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> During the 1990s, Parke-Davis, a subsidiary of Pfizer, used a number of illegal techniques to encourage physicians in the United States to prescribe gabapentin for unapproved uses.<ref name=Hen2006>Template:Cite journal</ref> They have paid out millions of dollars to settle lawsuits regarding these activities.<ref>Template:Cite news</ref>

Medical uses

Gabapentin is recommended for use in focal seizures and neuropathic pain.<ref name="Neurontin label" /><ref name="NICE">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Gabapentin is prescribed off-label in the US and the UK,<ref name="pmid30480717">Template:Cite journal</ref><ref name="pmid30907944">Template:Cite journal</ref> for example, for the treatment of non-neuropathic pain,<ref name="pmid30480717"/> anxiety disorders, sleep problems and bipolar disorder.<ref name="Sobel2012">Template:Cite book</ref> In recent years, gabapentin has seen increased use, particularly in the elderly.<ref>Template:Cite news</ref> There is concern regarding gabapentin's off-label use due to the lack of strong scientific evidence for its efficacy in multiple conditions, its proven side effects and its potential for misuse and physical/psychological dependency.<ref name="NIHR Evidence_2022" /><ref name="Hong_2022" /><ref>Template:Cite journal</ref> Some harms, including nervous system harms, have been underreported in published trials of gabapentin, potentially resulting in the underestimation of harms in guidelines for the use of gabapentin.<ref>Template:Cite journal</ref>

Seizures

Gabapentin is approved for the treatment of focal seizures;<ref>Template:Cite journal</ref> however, it is not effective for generalized epilepsy.<ref name="pmid24798217">Template:Cite journal</ref>

Neuropathic pain

Gabapentin is recommended as a first-line treatment for chronic neuropathic pain by various medical authorities.<ref name="NICE"/><ref name=Attal2010 /><ref name="pmid17372630">Template:Cite journal</ref><ref name="pmid25575710">Template:Cite journal</ref> This is a general recommendation applicable to all neuropathic pain syndromes except for trigeminal neuralgia, where it may be used as a second- or third-line agent.<ref name=Attal2010 /><ref name="pmid25575710"/>

Regarding the specific diagnoses, a systematic review has found evidence for gabapentin to provide pain relief for some people with postherpetic neuralgia and diabetic neuropathy.<ref name=Wiffen2017>Template:Cite journal</ref> Gabapentin is approved for the former indication in the US.<ref name="Neurontin label" /> In addition to these two neuropathies, European Federation of Neurological Societies guideline notes gabapentin effectiveness for central pain.<ref name=Attal2010 /> A combination of gabapentin with an opioid or nortriptyline may work better than either drug alone.<ref name=Attal2010 /><ref name="pmid25575710" />

Gabapentin shows substantial benefit (at least 50% pain relief or a patient global impression of change (PGIC) "very much improved") for neuropathic pain (postherpetic neuralgia or peripheral diabetic neuropathy) in 30–40% of subjects treated as compared to those treated with placebo.<ref name=Wiffen2017/>

Evidence finds little or no benefit and significant risk in those with chronic low back pain or sciatica.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Gabapentin is not effective in HIV-associated sensory neuropathy<ref>Template:Cite journal</ref> and neuropathic pain due to cancer.<ref name="pmid29486015">Template:Cite journal</ref>

Anxiety

There is a small amount of research on the use of gabapentin for the treatment of anxiety disorders.<ref name="pmid17502773">Template:Cite journal</ref><ref name="pmid29579375">Template:Cite journal</ref>

Gabapentin is effective for the long-term treatment of social anxiety disorder and in reducing preoperative anxiety.<ref name="NIHR Evidence_2022">Template:Cite journal</ref><ref name="Hong_2022">Template:Cite journal</ref>

In a controlled trial of breast cancer survivors with anxiety,<ref name="pmid29579375"/> and a trial for social phobia,<ref name="pmid17502773"/> gabapentin significantly reduced anxiety levels.

For panic disorder, gabapentin has produced mixed results.<ref name="pmid29579375" /><ref name="pmid17502773" /><ref name="Hong_2022" />

Sleep

Gabapentin is effective in treating sleep disorders such as insomnia and restless legs syndrome that are the result of an underlying illness, but comes with some risk of discontinuation and withdrawal symptoms after prolonged use at higher doses.<ref name="pmid28769860">Template:Cite journal</ref>

Gabapentin enhances slow-wave sleep in people with primary insomnia. It also improves sleep quality by elevating sleep efficiency and decreasing spontaneous arousal.<ref name="pmid20124884">Template:Cite journal</ref>

Drug dependence

Gabapentin is moderately effective in reducing the symptoms of alcohol withdrawal and associated craving.<ref>Template:Cite journal</ref><ref name="Berlin_2015">Template:Cite journal</ref><ref name="pmid31461226">Template:Cite journal</ref> The evidence in favor of gabapentin is weak in the treatment of alcoholism: it does not contribute to the achievement of abstinence, and the data on the relapse of heavy drinking and percent of days abstinent do not robustly favor gabapentin; it only decreases the percent days of heavy drinking.<ref name="pmid31077485">Template:Cite journal</ref>

Gabapentin is ineffective in cocaine dependence and methamphetamine use,<ref name="pmid29241365">Template:Cite journal</ref> and it does not increase the rate of smoking cessation.<ref>Template:Cite journal</ref> While some studies indicate that gabapentin does not significantly reduce the symptoms of opiate withdrawal, there is increasing evidence that gabapentinoids are effective in controlling some of the symptoms during opiate detoxification. A clinical study in Iran, where heroin dependence is a significant social and public health problem, showed gabapentin produced positive results during an inpatient therapy program, particularly by reducing opioid-induced hyperalgesia and drug craving.<ref name="pmid24250527">Template:Cite journal</ref><ref name="pmid29241365"/> There is insufficient evidence for its use in cannabis dependence.<ref>Template:Cite journal</ref>

Other

Gabapentin is recommended as a first-line treatment of the acquired pendular nystagmus, torsional nystagmus, and infantile nystagmus; however, it does not work in periodic alternating nystagmus.<ref>Template:Cite journal</ref><ref name="pmid22072056">Template:Cite journal</ref><ref name="pmid22661344">Template:Cite journal</ref>

Gabapentin decreases the frequency of hot flashes in both menopausal women and people with breast cancer. However, antidepressants have similar efficacy, and treatment with estrogen more effectively prevents hot flashes.<ref name="pmid31870736">Template:Cite journal</ref>

Gabapentin reduces spasticity in multiple sclerosis and is prescribed as one of the first-line options.<ref name="pmid27207462">Template:Cite journal</ref> It is an established treatment of restless legs syndrome.<ref name="pmid29756335">Template:Cite journal</ref> Gabapentin alleviates itching in kidney failure (uremic pruritus)<ref>Template:Cite journal</ref><ref name="pmid33283264">Template:Cite journal</ref> and itching of other causes.<ref>Template:Cite journal</ref> It may be an option in essential or orthostatic tremor.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Gabapentin does not appear to provide benefit for bipolar disorder,<ref name="Hong_2022" /><ref name="Berlin_2015"/><ref>Template:Cite journal</ref> complex regional pain syndrome,<ref>Template:Cite journal</ref> post-surgical pain,<ref>Template:Cite journal</ref> or tinnitus,<ref>Template:Cite journal</ref> or prevent episodic migraine in adults.<ref>Template:Cite journal</ref>

Contraindications

Gabapentin should be used carefully and at lower doses in people with kidney problems due to possible accumulation and toxicity. It is unclear if it is safe during pregnancy or breastfeeding.<ref name="Neurontin label" />

Side effects

File:Gabapentin Orion bottle.jpg

Gabapentin Orion 100 mg, bottle and pills in Sweden

Dizziness and somnolence are the most frequent side effects.<ref name="Neurontin label" /> Fatigue, ataxia, peripheral edema (swelling of extremities), and nystagmus are also common.<ref name="Neurontin label" /> A 2017 meta-analysis found that gabapentin also increased the risk of difficulties in mentation and visual disturbances as compared to a placebo.<ref>Template:Cite journal</ref> Gabapentin is associated with a weight gain of Template:Convert after 1.5 months of use.<ref name="pmid25590213">Template:Cite journal</ref> Case studies indicate that it may cause anorgasmia and erectile dysfunction,<ref name="pmid26559937">Template:Cite journal</ref> as well as myoclonus<ref name="pmid29111014">Template:Cite journal</ref><ref name="pmid30381161">Template:Cite journal</ref> that disappear after discontinuing gabapentin or replacing it with other medication. Fever, swollen glands that do not go away, eyes or skin turning yellow, unusual bruises or bleeding, unexpected muscle pain or weakness, rash, long-lasting stomach pain which may indicate an inflamed pancreas, hallucinations, anaphylaxis, respiratory depression, and increased suicidal ideation are rare but serious side effects.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Suicide

As with all antiepileptic drugs approved in the US, gabapentin label contains a warning of an increased risk of suicidal thoughts and behaviors.<ref name="Neurontin label">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This warning is based on a meta-analysis of all approved antiepileptic drugs in 2008, and not with gabapentin alone.<ref name="Patorno_2010" /> According to an experimental meta-analysis of insurance claims database, gabapentin use is associated with about 40% increased risk of suicide, suicide attempt and violent death as compared with a reference anticonvulsant drug topiramate. The risk is increased for people with bipolar disorder or epilepsy.<ref name="Patorno_2010">Template:Cite journal</ref> Another study has shown an approximately doubled rate of suicide attempts and self-harm in people with bipolar disorder who are taking gabapentin versus those taking lithium.<ref>Template:Cite journal</ref> A large Swedish study suggests that gabapentinoids are associated with an increased risk of suicidal behaviour, unintentional overdoses, head/body injuries, and road traffic incidents and offences.<ref>Template:Cite journal</ref> On the other hand, a study published by the Harvard Data Science Review found that gabapentin was associated with a significantly reduced rate of suicide.<ref>Gibbons, R., Hur, K., Lavigne, J., Wang, J., & Mann, J. J. (2019). Medications and Suicide: High Dimensional Empirical Bayes Screening (iDEAS). Harvard Data Science Review, 1(2). https://doi.org/10.1162/99608f92.6fdaa9de</ref>

Respiratory depression

Serious breathing suppression, potentially fatal, may occur when gabapentin is taken together with opioids, benzodiazepines, or other depressants, or by people with underlying lung problems such as COPD.<ref name="FDA breathing">{{#invoke:citation/CS1|citation |CitationClass=web }} Template:PD-notice</ref> Gabapentin and opioids are commonly prescribed or abused together, and research indicates that the breathing suppression they cause is additive. For example, gabapentin use before joint replacement or laparoscopic surgery increased the risk of respiratory depression by 30–60%.<ref name="FDA breathing" /> A Canadian study showed that use of gabapentin and other gabapentinoids, whether for epilepsy, neuropathic pain or other chronic pain was associated with a 35–58% increased risk for severe exacerbation of pre-existing chronic obstructive pulmonary disease.<ref>Template:Cite journal</ref>

Withdrawal and dependence

Withdrawal symptoms typically occur 1–2 days after abruptly stopping gabapentin (almost unambiguously due to extended use and during a very short-term rebound phenomenon) Template:Emdash similar to, albeit less intense than most benzodiazepines.<ref name="pmid26721643">Template:Cite journal</ref> Agitation, confusion and disorientation are the most frequently reported, followed by gastrointestinal complaints and sweating, and more rare tremor, tachycardia, hypertension and insomnia.<ref name="pmid26721643" /> In some cases, users experience withdrawal seizures after chronic or semi-chronic use in the absence of periodic cycles or breaks during repeating and consecutive use.<ref name="Bonnet_2017">Template:Cite journal</ref> All these symptoms subside when gabapentin is re-instated<ref name="pmid26721643" /> or tapered off gradually at an appropriate rate.Template:Citation needed

On its own, gabapentin appears to not have a substantial addictive power. In human and animal experiments, it shows limited to no rewarding effects. The vast majority of people abusing gabapentin are current or former abusers of opioids or sedatives.<ref name="Bonnet_2017" /> In these persons, gabapentin can boost the opioid "high" as well as decrease commonly experienced opioid-withdrawal symptoms such as anxiety.<ref>Template:Cite journal</ref>

Psychiatric and behavioral adverse effects

Gabapentin is increasingly recognized to cause a range of psychiatric and behavioral adverse effects that extend beyond its more common neurological side effects. Systematic reviews have documented atypical manifestations such as aggression, agitation, irritability, mood instability, and suicidal ideation, with some cases noting the emergence of mania, hallucinations, and psychosis, particularly in pediatric populations and individuals with preexisting psychiatric conditions.<ref name="Nwankwo_2024">Template:Cite journal</ref><ref name = "MC">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name = "Gál_2024">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Large cohort studies and post-marketing surveillance indicate that neuropsychiatric symptoms—including confusion, depression, and behavioral disturbances—can occur in up to 29% of gabapentin users, though most reactions are mild to moderate and often dose-dependent.<ref name="Huang_2023">Template:Cite journal</ref> There is also evidence associating gabapentin with an increased risk of suicidal behavior, especially in younger patients, and rare reports of violent or aggressive behavior, though causality is difficult to establish and such events remain uncommon.<ref name="Molero_2019">Template:Cite journal</ref><ref name="Athavale_2023">Template:Cite journal</ref>

Overdose

Through excessive ingestion, accidental or otherwise, persons may experience overdose symptoms including drowsiness, sedation, blurred vision, slurred speech, somnolence, uncontrollable jerking motions, and anxiety. A very high amount taken is associated with breathing suppression, coma, and possibly death, particularly if combined with alcohol or opioids.<ref name="Bonnet_2017" /><ref>R.C. Baselt, Disposition of Toxic Drugs and Chemicals in Man, 8th edition, Biomedical Publications, Foster City, CA, 2008, pp. 677–8. Template:ISBN.</ref>

Pharmacology

Animal Models

Gabapentin, prevents seizures in a dose-related manner in several laboratory animal models.<ref>Template:Cite journal</ref> These models include spinal extensor seizures from low-intensity electroshock to the forebrain in mice, maximal electroshock in rats, spinal extensor seizures in DBA/2 mice with a genetic sensitivity to seizures induced by loud noise, and in rats "kindled" to produce focal seizures by repeated prior electrical stimulation of the hippocampus. Gabapentin slightly increased spontaneous absence-like seizures in a genetically susceptible strain recorded with electroencephalography. All of these effects of gabapentin were seen at dosages at or below the threshold for producing ataxia.

Gabapentin also has been tested in a wide variety of animal models that are relevant for analgesic actions.<ref>Template:Cite journal</ref> Generally, gabapentin is not active to prevent pain-related behaviors in models of acute nociceptive pain, but it prevents pain-related behaviors when animals are made sensitive by prior peripheral inflammation or peripheral nerve damage (inflammatory or neuropathic conditions).

Pharmacodynamics

Gabapentin is a ligand of the α₂δ calcium channel subunit.<ref name="pmid16376147">Template:Cite journal</ref><ref name="pmid27345098">Template:Cite journal</ref> The α₂δ-1 protein is coded by the CACNA2D1 gene. α₂δ was first described as an auxiliary protein connected to the main α₁ subunit (the channel-forming protein) of high voltage activated voltage-dependent calcium channels (L-type, N-type, P/Q type, and R-type).<ref name="pmid32521436">Template:Cite journal</ref> The same α₂δ protein has more recently been shown to interact directly with some NMDA-type and AMPA-type glutamate receptors at presynaptic sites and also with thrombospondin (an extracellular matrix protein secreted by astroglial cells).<ref>Template:Cite journal</ref>

Gabapentin is not a direct calcium channel blocker: it exerts its actions by disrupting the regulatory function of α₂δ and its interactions with other proteins. Gabapentin reduces delivery of intracellular calcium channels to the cell membrane, reduces the activation of the channels by the α₂δ subunit, decreases signaling leading to neurotransmitters release, and disrupts interactions of α₂δ with voltage gated calcium channels but also with NMDA receptors, neurexins, and thrombospondin.<ref name="pmid32521436" /><ref name="pmid23642658">Template:Cite journal</ref><ref name="pmid32321743">Template:Cite journal</ref> These proteins are found as mutually interacting parts of the presynaptic active zone, where numerous protein molecules interact with each other to enable and to regulate the release of neurotransmitters from presynaptic vesicles into the synaptic space.Template:Fact

Out of the four known isoforms of α₂δ protein, gabapentin binds with similar high affinity to two: α₂δ-1 and α₂δ-2.<ref name="pmid27345098" /> All of the pharmacological properties of gabapentin tested to date are explained by its binding to just one isoform – α₂δ-1.<ref name="pmid27345098" /><ref name="pmid23642658" />

The endogenous α-amino acids L-leucine and L-isoleucine, which resemble gabapentin in chemical structure, bind α₂δ with similar affinity to gabapentin and are present in human cerebrospinal fluid at micromolar concentrations.<ref name="pmid17222465">Template:Cite journal</ref> They may be the endogenous ligands of the α₂δ subunit, and they competitively antagonize the effects of gabapentin.<ref name="pmid17222465" /><ref name="pmid17403543">Template:Cite journal</ref> Accordingly, while gabapentin has nanomolar affinity for the α₂δ subunit, its potency in vivo is in the low micromolar range, and competition for binding by endogenous L-amino acids is likely to be responsible for this discrepancy.<ref name="pmid23642658"/>

Gabapentin is a potent activator of voltage-gated potassium channels KCNQ3 and KCNQ5, even at low nanomolar concentrations. However, this activation is unlikely to be the dominant mechanism of gabapentin's therapeutic effects.<ref name="pmid30021858">Template:Cite journal</ref>

Gabapentin is structurally similar to the neurotransmitter glutamate and competitively inhibits branched-chain amino acid aminotransferase (BCAT), slowing down the synthesis of glutamate.<ref name="inhibition">Template:Cite journal</ref> In particular, it inhibits BCAT-1 at high concentrations (K_i = 1 mM), but not BCAT-2.<ref name="BCAT">Template:Cite journal</ref> At very high concentrations gabapentin can suppress the growth of cancer cells, presumably by affecting mitochondrial catabolism, however, the precise mechanism remains elusive.<ref name="BCAT"/>

Even though gabapentin is a structural GABA analogue, and despite its name, it does not bind to the GABA receptors, does not convert into Template:Abbrlink or another GABA receptor agonist in vivo, and does not modulate GABA transport or metabolism within the range of clinical dosing.<ref name="pmid16376147" /> In vitro gabapentin has been found to very weakly inhibit the GABA aminotransferase enzyme (K_i = 17–20 mM), however, this effect is so weak it is not clinically relevant at prescribed doses.<ref name="inhibition"/>

Pharmacokinetics

Gabapentin is absorbed from the intestines by an active transport process mediated via an amino acid transporter, presumably, LAT2.<ref name="pmid18656534">Template:Cite journal</ref> As a result, the pharmacokinetics of gabapentin is dose-dependent, with diminished bioavailability and delayed peak levels at higher doses.<ref name="pmid27345098" />

The oral bioavailability of gabapentin is approximately 80% at 100 mg administered three times daily once every 8 hours, but decreases to 60% at 300 mg, 47% at 400 mg, 34% at 800 mg, 33% at 1,200 mg, and 27% at 1,600 mg, all with the same dosing schedule.<ref name="Neurontin label" /><ref name="pmid20818832">Template:Cite journal</ref> Drugs that increase the transit time of gabapentin in the small intestine can increase its oral bioavailability; when gabapentin was co-administered with oral morphine, the oral bioavailability of a 600 mg dose of gabapentin increased by 50%.<ref name="pmid20818832" />

Gabapentin at a low dose of 100 mg has a T_max (time to peak levels) of approximately 1.7 hours, while the T_max increases to 3 to 4 hours at higher doses.<ref name="pmid27345098" /> Food does not significantly affect the T_max of gabapentin and increases the C_max and area-under-curve levels of gabapentin by approximately 10%.<ref name="pmid20818832" />

Gabapentin can cross the blood–brain barrier and enter the central nervous system.<ref name="pmid16376147" /> Gabapentin concentration in cerebrospinal fluid is approximately 9–14% of its blood plasma concentration.<ref name="pmid20818832"/> Due to its low lipophilicity,<ref name="pmid20818832" /> gabapentin requires active transport across the blood–brain barrier.<ref name="pmid23567998">Template:Cite journal</ref><ref name="pmid16376147" /><ref name="pmid26305616">Template:Cite journal</ref><ref name="pmid19937841">Template:Cite journal</ref> The LAT1 is highly expressed at the blood–brain barrier<ref name="pmid10518579">Template:Cite journal</ref> and transports gabapentin across into the brain.<ref name="pmid23567998" /><ref name="pmid16376147" /><ref name="pmid26305616" /><ref name="pmid19937841" /> As with intestinal absorption mediated by an amino acid transporter, the transport of gabapentin across the blood–brain barrier by LAT1 is saturable.<ref name="pmid23567998" /> Gabapentin does not bind to other drug transporters such as P-glycoprotein (ABCB1) or OCTN2 (SLC22A5).<ref name="pmid23567998" /> It is not significantly bound to plasma proteins (<1%).<ref name="pmid20818832" />

Gabapentin undergoes little or no metabolism.<ref name="pmid27345098" /><ref name="pmid20818832" />

Gabapentin is generally safe in people with liver cirrhosis.<ref name="pmid37918778">Template:Cite journal</ref>

Gabapentin is eliminated renally in the urine.<ref name="pmid20818832" /> It has a relatively short elimination half-life, with the reported average value of 5 to 7 hours.<ref name="pmid20818832" /> Because of its short elimination half-life, gabapentin must be administered 3 to 4 times per day to maintain therapeutic levels.<ref name="pmid20505847">Template:Cite journal</ref> Gabapentin XR (brand name Gralise) is taken once a day.<ref name="Kaye2017">Template:Cite book</ref>

Chemistry

File:Gaba and gabapentin.png

Chemical structures of GABA and gabapentin, with commonalities highlighted

Gabapentin is a 3,3-disubstituted derivative of GABA. Therefore, it is a GABA analogue, as well as a γ-amino acid.<ref name="WyllieCascino2012">Template:Cite book</ref><ref name="BenzonRathmell2013">Template:Cite book</ref> It is similar to several other compounds that collectively are called gabapentinoids. Specifically, it is a derivative of GABA with a pentyl disubstitution at 3 position, hence, the name - gabapentin, in such a way as to form a six-membered ring. After the formation of the ring, the amine and carboxylic groups are not in the same relative positions as they are in the GABA;<ref name="Sneader2005">Template:Cite book</ref> they are more conformationally constrained.<ref name="pmid21428817">Template:Cite journal</ref>

Although it has been known for some time that gabapentin must bind to the α₂δ-1 protein in order to act pharmacologically (see Pharmacodynamics), the three-dimensional structure of the α₂δ-1 protein with gabapentin bound (or alternatively, the native amino acid, L-Isoleucine bound) has only recently been obtained by cryo-electron microscopy.<ref>Template:Cite journal</ref> A figure of this drug-bound structure is shown in the Chemistry section of the entry on gabapentinoid drugs. This study confirms other findings to show that both compounds alternatively can bind at a single extracellular site (somewhat distant from the calcium conducting pore of the voltage gated calcium channel α1 subunit) on the calcium channel and chemotaxis (Cache1) domain of α₂δ-1.

Synthesis

File:Synthesis of gabapentin.png

Synthesis of gabapentin.

A process for chemical synthesis and isolation of gabapentin with high yield and purity<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> starts with conversion of 1,1-cyclohexanediacetic anhydride to 1,1-cyclohexanediacetic acid monoamide and is followed by a 'Hofmann' rearrangement in an aqueous solution of sodium hypobromite prepared in situ.

History

GABA is the principal inhibitory neurotransmitter in mammalian brain. By the early 1970s, it was appreciated that there are two main classes of GABA receptors, GABA_A and GABA_B and also that baclofen was an agonist of GABA_B receptors. Gabapentin was designed, synthesized and tested in mice by researchers at the pharmaceutical company Goedecke AG in Freiburg, Germany (a subsidiary of Parke-Davis). It was meant to be an analogue of the neurotransmitter GABA that could more easily cross the blood–brain barrier. It was first synthesized in 1974/75 and described in 1975<ref name="US4024175">Template:Cite patent</ref> by Satzinger and Hartenstein.<ref name="Sneader2005" /><ref name="JohnsonLi2013">Template:Cite book</ref>

The first pharmacology findings published were sedating properties and prevention of seizures in mice evoked by the GABA antagonist, thiosemicarbazide.<ref name="US4024175" /> Shortly after, gabapentin was shown in vitro to reduce the release of the neurotransmitter dopamine from slices of rat caudate nucleus (striatum).<ref>Template:Cite journal</ref> This study provided evidence that the action of gabapentin, unlike baclofen, did not arise from the GABA_B receptor.

Initial clinical trials utilizing small numbers of subjects were for treatment of spasticity<ref>Template:Cite journal</ref> and migraine<ref>Template:Cite journal</ref> but neither study had statistical power to allow conclusions. In 1987, the first positive results with gabapentin were obtained in a clinical trial using three dose groups versus pre-treatment seizure frequency for 75 days, as add-on treatment in patients who still had seizures despite taking other medications.<ref>Template:Cite journal</ref> This study did not show statistically significant results, but it did show a strong dose-related trend to decreased frequency of seizures.

Under the brand name Neurontin, it was first approved in the United Kingdom in May 1993, for the treatment of refractory epilepsy.<ref name="AdisInsight-Gabapentin">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Approval by the U.S. Food and Drug Administration followed in December 1993, also for use as an adjuvant (effective when added to other antiseizure drugs) medication to control partial seizures in adults; that indication was extended to children in 2000.<ref name="Mack">Template:Cite journal</ref><ref name="Neurontin label" /> Subsequently, gabapentin was approved in the United States for the treatment of pain from postherpetic neuralgia in 2002.<ref name="pmid23342236">Template:Cite journal</ref> A generic version of gabapentin first became available in the United States in 2004.<ref name="Reed2012">Template:Cite book</ref> An extended-release formulation of gabapentin for once-daily administration, under the brand name Gralise, was approved in the United States for the treatment of postherpetic neuralgia in January 2011.<ref name="GoodRx2013">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="AdisInsight-Gabapentin-CR">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In recent years, gabapentin has been prescribed for an increasing range of disorders and is one of the more common medications used, particularly in elderly people.<ref>Template:Cite news</ref>

Society and culture

Legal status

United Kingdom

Effective April 2019, the United Kingdom reclassified the drug as a class C controlled substance.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref><ref name="UK class C">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

United States

Gabapentin is not a controlled substance under the federal Controlled Substances Act.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Effective 1 July 2017, Kentucky classified gabapentin as a schedule V controlled substance statewide.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Gabapentin is scheduled V drug in other states such as West Virginia,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Tennessee,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Alabama,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Utah,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and Virginia.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Off-label promotion

Although some small, non-controlled studies in the 1990s—mostly sponsored by gabapentin's manufacturer—suggested that treatment for bipolar disorder with gabapentin may be promising,<ref name="evid">Template:Cite journal</ref> the preponderance of evidence suggests that it is not effective.<ref>Template:Cite journal</ref>

Franklin v. Parke-Davis case

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After the corporate acquisition of the original patent holder, the pharmaceutical company Pfizer admitted that there had been violations of FDA guidelines regarding the promotion of unproven off-label uses for gabapentin in the Franklin v. Parke-Davis case.

While off-label prescriptions are common for many drugs, marketing of off-label uses of a drug is not.<ref name=Hen2006 /> In 2004, Warner-Lambert (which subsequently was acquired by Pfizer) agreed to plead guilty for activities of its Parke-Davis subsidiary, and to pay $430 million in fines to settle civil and criminal charges regarding the marketing of Neurontin for off-label purposes. The 2004 settlement was one of the largest in U.S. history up to that point, and the first off-label promotion case brought successfully under the False Claims Act.<ref>Template:Cite news</ref>

Kaiser Foundation Hospitals and Kaiser Foundation Health Plan sued Pfizer Inc., alleging that the pharmaceutical company had misled Kaiser by recommending Neurontin as an off-label treatment for certain conditions (including bipolar disorder, migraines, and neuropathic pain).<ref name="Berkrot 20100325">Template:Cite news</ref><ref name=AP2010Jury>Template:Cite news</ref><ref>Template:Cite news</ref> In 2010, a federal jury in Massachusetts ruled in Kaiser's favor, finding that Pfizer violated the federal Racketeer Influenced and Corrupt Organizations (RICO) Act and was liable for Template:US$ in damages, which was automatically trebled to just under $142.1 million.<ref name=AP2010Jury/><ref name="Berkrot 20100325"/> Aetna, Inc. and a group of employer health plans prevailed in their similar Neurontin-related claims against Pfizer.<ref name=Husgen>Template:Cite news</ref> Pfizer appealed, but the U.S. Court of Appeals for the First Circuit upheld the verdict,<ref name=Husgen/> and in 2013, the US Supreme Court declined to hear the case.<ref>Template:Cite news</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Gabasync

Gabasync, a treatment consisting of a combination of gabapentin and two other medications (flumazenil and hydroxyzine) as well as therapy, is an ineffective treatment promoted for methamphetamine addiction, though it had also been claimed to be effective for dependence on alcohol or cocaine.<ref name = "Pelley_2007" /> It was marketed as PROMETA. While the individual drugs had been approved by the FDA, their off-label use for addiction treatment has not.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Gabasync was marketed by Hythiam, Inc. which is owned by Terren Peizer, a former junk bond salesman who has since been convicted of securities fraud relative to another company.<ref>Dave Michaels (21 June 2024). "Jury Convicts Milken Protégé Terren Peizer of Insider Trading," The Wall Street Journal.</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name = "Pelley_2007">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Hythiam charges up to $15,000 per patient to license its use (of which half goes to the prescribing physician, and half to Hythiam).<ref>Template:Cite journal</ref>

In a November 2005 article entitled "Curb Your Cravings For This Stock", Barrons wrote: "If the venture works out for patients and the investing public, it'll be a rare success for Peizer, who's promoted a series of disappointing small-cap medical or technology stocks ... since his days at Drexel".<ref name="Alpert_2005">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 60 Minutes, NBC News, and The Dallas Morning News criticized Peizer after the company bypassed clinical studies and government approval when bringing to market Prometa; the addiction drug proved to be completely ineffective.<ref name="Huus_2007">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite news</ref><ref name = "Pelley_2007" /><ref name="Dallas">Template:Cite news</ref> CBS News journalist Scott Pelley said to Peizer in 2007: "Depending on who you talk to, you're either a revolutionary or a snake oil salesman."<ref name="Schuster_2007">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Alpert_2005"/> Journalist Adam Feuerstein opined: "most of what Peizer says is dubious-sounding hype".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In November 2011, the results of a double-blind, placebo-controlled study (financed by Hythiam and carried out at UCLA) were published in the peer-reviewed journal Addiction. It concluded that Gabasync is ineffective: "The PROMETA protocol, consisting of flumazenil, gabapentin and hydroxyzine, appears to be no more effective than placebo in reducing methamphetamine use, retaining patients in treatment or reducing methamphetamine craving."<ref>Template:Cite journal</ref>

Usage trends

The period from 2008 to 2018 saw a significant increase in the consumption of gabapentinoids. A study published in Nature Communications in 2023 highlights this trend, demonstrating a notable escalation in sales of gabapentinoids. The study, which analyzed healthcare data across 65 countries/ regions, found that the consumption rate of gabapentinoids had doubled over the decade, driven by their use in a wide range of indications.<ref>Template:Cite journal</ref>

Brand names

Gabapentin was originally marketed under the brand name Neurontin. Since it became generic, it has been marketed worldwide using over 300 different brand names.<ref name="Drugs.com" >{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> An extended-release formulation of gabapentin for once-daily administration was introduced in 2011, for postherpetic neuralgia under the brand name Gralise.<ref name="Drugs.com-History">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In the US, Neurontin is marketed by Viatris after Upjohn was spun off from Pfizer.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Related drugs

Parke-Davis developed a drug called pregabalin, which is related in structure to gabapentin, as a successor to gabapentin.<ref name="Baillie 33–9">Template:Cite journal</ref> Another similar drug atagabalin has been unsuccessfully tried by Pfizer as a treatment for insomnia.<ref name="pmid21681607">Template:Cite journal</ref> A prodrug form (gabapentin enacarbil)<ref name="pmid19787095">Template:Cite journal</ref> was approved by the U.S. Food and Drug Administration (FDA).

Recreational use

Template:Globalize section When taken in excess, gabapentin can induce euphoria, a sense of calm, improved sociability, and reduced alcohol or cocaine cravings.<ref name="pmid22867659">Template:Cite journal</ref><ref>Template:Cite journal</ref><ref name="pmid31291212">Template:Cite journal</ref> Also known on the streets as "Gabbies",<ref>Template:Cite book</ref> gabapentin was reported in 2017 to be increasingly abused and misused for these euphoric effects.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> About 1 percent of the responders to an Internet poll and 22 percent of those attending addiction facilities had a history of abuse of gabapentin.<ref name="pmid26721643" /><ref name="pmid29179227">Template:Cite journal</ref> Gabapentin misuse, toxicity, and use in suicide attempts among adults in the US increased from 2013 to 2017.<ref>Template:Cite journal</ref>

After Kentucky implemented stricter legislation regarding opioid prescriptions in 2012, there was an increase in gabapentin-only and multi-drug use from 2012 to 2015. The majority of these cases were from overdose in suspected suicide attempts. These rates were also accompanied by increases in abuse and recreational use.<ref>Template:Cite journal</ref>

Withdrawal symptoms, often resembling those of benzodiazepine withdrawal, play a role in the physical dependence some users experience.<ref name="Bonnet_2017" /> Its misuse predominantly coincides with the usage of other CNS depressant drugs, namely opioids, benzodiazepines, and alcohol.<ref>Template:Cite journal</ref>

Veterinary use

In cats, gabapentin can be used as an analgesic in multi-modal pain management,<ref name="pmid21831060">Template:Cite journal</ref> anxiety medication to reduce stress during travel or vet visits,<ref name="pmid29099247">Template:Cite journal</ref> and anticonvulsant.<ref name=plumbs>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Veterinarians may prescribe gabapentin as an anticonvulsant and pain reliever in dogs.<ref name="Coile_2022" /><ref name="plumbs" /> It has beneficial effects for treating epilepsy, different kinds of pain (chronic, neuropathic, and post-operative pain), and anxiety, lip-licking behaviour, storm phobia, fear-based aggression.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

It is also used to treat chronic pain-associated nerve inflammation in horses and dogs. Side effects include tiredness and loss of coordination, but these effects generally go away within 24 hours of starting the medication.<ref name="Coile_2022">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="plumbs" />

See also

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