Gabapentin was first approved for use in 1993. It has been available as a generic medication in the United States since 2004. The wholesale price in the developing world as of 2015[update] was about US$10.80 per month; in the United States, it was US$100 to US$200. In 2016, it was the 11th most prescribed medication in the United States, with more than 44 million prescriptions. During the 1990s, Parke-Davis, a subsidiary of Pfizer, began using a number of illegal techniques to encourage physicians in the United States to use gabapentin for unapproved uses. They have paid out millions of dollars to settle lawsuits regarding these activities.
A 2017 Cochrane review found evidence of moderate quality showing a reduction in pain by 50% in about 15% of people with postherpetic neuralgia and diabetic neuropathy. Evidence finds little benefit and significant risk in those with chronic low back pain. It is not known if gabapentin can be used to treat other pain conditions, and no difference among various formulations or doses of gabapentin was found.
A 2009 review found gabapentin may reduce opioid use following surgery, but does not help with post-surgery chronic pain. A 2016 review found it does not help with pain following a knee replacement.
It appears to be as effective as pregabalin for neuropathic pain and costs less. All doses appear to result in similar pain relief.
The American Headache Society (AHS) and American Academy of Neurology (AAN) guidelines classify gabapentin as a drug with "insufficient data to support or refute use for migraine prophylaxis". A 2013 Cochrane review concluded that gabapentin was not useful for the prevention of episodic migraine in adults.
Gabapentin has been used off-label for the treatment of anxiety disorders. However, there is dispute over whether evidence is sufficient to support it being routinely prescribed for this purpose. While pregabalin may have efficacy in the treatment of refractory anxiety in people with chronic pain, it is unclear if gabapentin is equally effective.
Gabapentin may be useful in the treatment of comorbid anxiety in bipolar patients; however, it is not effective as a mood-stabilizing treatment for manic or depressive episodes themselves. Other psychiatric conditions, such as borderline personality disorder, have also been treated off-label with gabapentin. There is insufficient evidence to support its use in obsessive–compulsive disorder and treatment-resistant depression.
Gabapentin may reduce symptoms of alcohol withdrawal (but it does not prevent the associated seizures), alcohol dependence and craving. There is some evidence for its role in the treatment of alcohol use disorder; the 2015 VA/DoD guideline on substance use disorders lists gabapentin as a "weak for" and is recommended as a second-line agent. Use for smoking cessation has had mixed results. There is insufficient evidence for its use in cannabis dependence.
Some have suggested avoiding gabapentin in people with a history of myoclonus or myasthenia gravis, as it may induce or mimic the symptoms of these two conditions.
In 2009 the U.S. Food and Drug Administration (FDA) issued a warning of an increased risk of suicidal thoughts and behaviors in patients taking some anticonvulsant drugs, including gabapentin, modifying the packaging inserts to reflect this. A 2010 meta-analysis supported the increased risk of suicide associated with gabapentin use.
Studies have also shown an almost doubled rate of suicidal ideation in patients with bipolar disorder who are taking gabapentin versus those on lithium.
An increase in formation of adenocarcinomas was observed in rats during preclinical trials; however, the clinical significance of these results remains undetermined. Gabapentin is also known to induce pancreatic acinar cell carcinomas in rats through an unknown mechanism, perhaps by stimulation of DNA synthesis; these tumors did not affect the lifespan of the rats and did not metastasize.
Abuse and addiction
Surveys suggest that approximately 1.1 percent of the general population and 22 percent of those attending addiction facilities have a history of abuse of gabapentin.
While the mechanisms behind its abuse potential are not well understood, gabapentin misuse has been recorded across a range of doses, including those that are considered therapeutic. Abuse often coincides with other substance use disorders, most commonly opioids. Mechanistically, the GABAmimetic properties of gabapentin can induce a euphoria that augments the effects of the opioid being used, as well aiding in the cessation of commonly experienced opioid-withdrawal symptoms, such as anxiety.
Misuse of this drug have been recorded for a number of reasons, including self-medication, self-harm and recreational use. Withdrawal symptoms, often resembling those of benzodiazepine withdrawal, play a role in the physical dependence some user experience.
Tolerance and withdrawal symptoms are a common occurrence in prescribed therapeutic users as well as non-medical recreational users. Withdrawal symptoms typically emerge within 12 hours to 7 days after stopping gabapentin. Some of the most commonly reported withdrawal symptoms include agitation, confusion, disorientation, upset stomach and sweating. In some cases, users experienced delirium and withdrawal seizures, which may only respond to the re-administration of gabapentin.
Through excessive ingestion, accidental or otherwise, persons may experience overdose symptoms including drowsiness, sedation, blurred vision, slurred speech, somnolence, uncontrollable jerking motions, anxiety and possibly death, if a very high amount was taken, particularly if combined with alcohol. For overdose considerations, serum gabapentin concentrations may be measured for confirmation.
The endogenousα-amino acidsL-leucine and L-isoleucine, which closely resemble gabapentin and the other gabapentinoids in chemical structure, are apparent ligands of the α2δ VDCC subunit with similar affinity as the gabapentinoids (e.g., IC50 = 71 nM for L-isoleucine), and are present in human cerebrospinal fluid at micromolar concentrations (e.g., 12.9 μM for L-leucine, 4.8 μM for L-isoleucine). It has been theorized that they may be the endogenous ligands of the subunit and that they may competitively antagonize the effects of gabapentinoids. In accordance, while gabapentinoids like gabapentin and pregabalin have nanomolar affinities for the α2δ subunit, their potencies in vivo are in the low micromolar range, and competition for binding by endogenous L-amino acids has been said to likely be responsible for this discrepancy.
The oralbioavailability 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. Food increases the area-under-curve levels of gabapentin by about 10%. 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 (which slows intestinalperistalsis), the oral bioavailability of a 600 mg dose of gabapentin increased by 50%. The oral bioavailability of gabapentin enacarbil (as gabapentin) is greater than or equal to 68%, across all doses assessed (up to 2,800 mg), with a mean of approximately 75%.
Gabapentin at a low dose of 100 mg has a Tmax (time to peak levels) of approximately 1.7 hours, while the Tmax increases to 3 to 4 hours at higher doses. Food does not significantly affect the Tmax of gabapentin and increases the Cmax of gabapentin by approximately 10%. The Tmax of the instant-release (IR) formulation of gabapentin enacarbil (as active gabapentin) is about 2.1 to 2.6 hours across all doses (350–2,800 mg) with single administration and 1.6 to 1.9 hours across all doses (350–2,100 mg) with repeated administration. Conversely, the Tmax of the extended-release (XR) formulation of gabapentin enacarbil is about 5.1 hours at a single dose of 1,200 mg in a fasted state and 8.4 hours at a single dose of 1,200 mg in a fed state.
Gabapentin is eliminatedrenally in the urine. It has a relatively short elimination half-life, with a reported value of 5.0 to 7.0 hours. Similarly, the terminal half-life of gabapentin enacarbil IR (as active gabapentin) is short at approximately 4.5 to 6.5 hours. The elimination half-life of gabapentin has been found to be extended with increasing doses; in one series of studies, it was 5.4 hours for 200 mg, 6.7 hours for 400 mg, 7.3 hours for 800 mg, 9.3 hours for 1,200 mg, and 8.3 hours for 1,400 mg, all given in single doses. Because of its short elimination half-life, gabapentin must be administered 3 to 4 times per day to maintain therapeutic levels. Conversely, gabapentin enacarbil is taken twice a day and gabapentin XR (brand name Gralise) is taken once a day.
Chemical structures of GABA, gabapentin, and two other gabapentinoids, pregabalin and phenibut.
Gabapentin was developed at Parke-Davis and was first described in 1975. Under the brand name Neurontin, it was first approved in May 1993 for the treatment of epilepsy in the United Kingdom, and was marketed in the United States in 1994. Subsequently, gabapentin was approved in the United States for the treatment of postherpetic neuralgia in May 2002. A generic version of gabapentin first became available in the United States in 2004. An extended-release formulation of gabapentin for once-daily administration, under the brand name Gralise, was approved in the United States for the treatment postherpetic neuralgia in January 2011. Gabapentin enacarbil was introduced in the United States for the treatment of restless legs syndrome in 2011 and was approved for the treatment of postherpetic neuralgia in 2012.
Society and culture
Gabapentin is best known under the brand name Neurontin manufactured by Pfizer subsidiary Parke-Davis. A Pfizer subsidiary named Greenstone markets generic gabapentin.
In December 2004 the FDA granted final approval to a generic equivalent to Neurontin made by the Israeli firm Teva.
Neurontin began as one of Pfizer's best selling drugs; however, Pfizer was criticized and under litigation for its marketing of the drug (see Franklin v. Parke-Davis). Pfizer faced allegations that Parke-Davis marketed the drug for at least a dozen off-label uses that the FDA had not approved. It has been used as a mainstay drug for migraines, even though it was not approved for such use in 2004.
Gabapentin was originally approved by the U.S. Food and Drug Administration (FDA) in December 1993, 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. In 2004, its use for treating postherpetic neuralgia (neuropathic pain following shingles) was approved.
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, the preponderance of evidence suggests that it is not effective. Subsequent to 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.
Reuters reported on 25 March 2010, that "Pfizer Inc violated federal racketeering law by improperly promoting the epilepsy drug Neurontin ... Under federal RICO law the penalty is automatically tripled, so the finding will cost Pfizer $141 million." The case stems from a claim from Kaiser Foundation Health Plan Inc. that "it was misled into believing Neurontin was effective for off-label treatment of migraines, bipolar disorder and other conditions. Pfizer argued that Kaiser physicians still recommend the drug for those uses."
Bloomberg News reported "during the trial, Pfizer argued that Kaiser doctors continued to prescribe the drug even after the health insurer sued Pfizer in 2005. The insurer's website also still lists Neurontin as a drug for neuropathic pain, Pfizer lawyers said in closing argument."
The Wall Street Journal noted that Pfizer spokesman Christopher Loder said, "We are disappointed with the verdict and will pursue post-trial motions and an appeal." He would later add that "the verdict and the judge's rulings are not consistent with the facts and the law."
According to the San Francisco Chronicle, off-label prescriptions accounted for roughly 90 percent of Neurontin sales.
While off-label prescriptions are common for a number of drugs, marketing of off-label uses of a drug is not. 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, and the first off-label promotion case brought successfully under the False Claims Act.
Gabapentin was originally marketed under the brand name Neurontin. Since it became generic, it has been marketed worldwide using over 300 different brand names. An extended-release formulation of gabapentin for once-daily administration was introduced in 2011 for postherpetic neuralgia under the brand name Gralise.
A capsule of gabapentin.
Parke-Davis developed a drug called pregabalin as a successor to gabapentin. Pregabalin was brought to market by Pfizer as Lyrica after the company acquired Warner-Lambert. Pregabalin is related in structure to gabapentin. Another new drug atagabalin has been trialed by Pfizer as a treatment for insomnia.
Also known on the streets as "Gabbies", gabapentin is increasingly being abused and misused for its euphoric effects. Furthermore, its misuse predominantly coincides with the usage of other illicit drugs, namely opioids, benzodiazepines, and alcohol.
After Kentucky's implementation of stricter legislation regarding opioid prescriptions in 2012, there was an increase in gabapentin-only and multi-drug use in 2012–2015. The majority of these cases were from overdose in suspected suicide attempts. These rates were also accompanied by increases in abuse and recreational use.
In cats, gabapentin can be used as an analgesic in multi-modal pain management. It is also used as an anxiety medication to reduce stress in cats for travel or vet visits.
Gabapentin is also used in dogs and other animals, but some formulations (especially liquid forms) meant for human use contain the sweetener xylitol, which is toxic to dogs.
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