Zolpidem was approved for medical use in the United States in 1992.[11][21] It became available as a generic medication in 2007.[22] Zolpidem is a schedule IV controlled substance under the Controlled Substances Act of 1970 (CSA).[7][8] More than ten million prescriptions are filled each year in the United States, making it one of the most commonly used treatments for sleeping problems.[23][24] In 2022, it was the 66th most commonly prescribed medication in the United States, with more than 9million prescriptions.[25][26]
Medical uses
Zolpidem is labeled for short-term (usually about two to six weeks) treatment of insomnia at the lowest possible dose.[11][16] It may be used for both improving sleep onset, sleep onset latency, and staying asleep.[7]
Guidelines from NICE, the European Sleep Research Society, and the American College of Physicians recommend medication for insomnia (including possible zolpidem) only as a second-line treatment after non-pharmacological treatment options have been tried (e.g. cognitive behavioral therapy for insomnia).[17][18][19] This is based in part on a 2012 review which found that zolpidem's effectiveness is nearly as much due to psychological effects as to the medication itself.[27]
Contraindications
Use of zolpidem may impair driving skills with a resultant increased risk of road traffic accidents. This adverse effect is not unique to zolpidem but also occurs with other hypnotic drugs. Caution should be exercised by motor vehicle drivers.[16] The U.S. Food and Drug Administration (FDA) recommends lower doses of zolpidem due to impaired function the day after taking it.[28][29][30][31][32]
Zolpidem should not be prescribed to older people, who are more sensitive to the effects of hypnotics including zolpidem, and are at an increased risk of falls and adverse cognitive effects, such as delirium and neurocognitive disorder.[33][34]
Animal studies have revealed evidence of incomplete ossification and increased intrauterine fetal death at doses greater than seven times the maximum recommended human dose or higher; however, teratogenicity was not observed at any dose level. There are no controlled data on human pregnancy. In one case report, zolpidem was found in cord blood at delivery. Zolpidem is recommended for use during pregnancy only when the benefits outweigh the risks.[35]
Adverse effects
The most common adverse effects of short-term use include headache (reported by 7% of people in clinical trials), drowsiness (2%), dizziness (1%), and diarrhea (1%); the most common side effects of long-term use included
drowsiness (8%),
dizziness (5%),
allergy (4%),
sinusitis (4%),
back pain (3%),
diarrhea (3%),
drugged feeling (3%),
dry mouth (3%),
lethargy (3%),
sore throat (3%),
abdominal pain (2%),
constipation (2%),
heart palpitations (2%),
lightheadedness (2%),
rash (2%),
abnormal dreams (1%),
amnesia (1%),
chest pain (1%),
depression (1%),
flu-like symptoms (1%),
and sleep disorder (1%).[8]
Zolpidem increases the risk of depression, falls and bone fracture, poor driving, suppressed respiration and has been associated with an increased risk of death.[36] Upper and lower respiratory infections are also common (experienced by 1–10% of people).[16]
Residual 'hangover' effects, such as sleepiness and impaired psychomotor and cognitive function, may persist into the day following nighttime administration. Such effects may impair the ability of users to drive safely and increase risks of falls and hip fractures.[20][37] Around 3% of people taking zolpidem are likely to break a bone as a result of a fall due to impaired coordination caused by the drug.[38]
Some users have reported unexplained sleepwalking while using zolpidem, as well as sleep-driving, night eating syndrome while asleep, and performing other daily tasks while sleeping.[20] Research by Australia's National Prescribing Service found these events occur mostly after the first dose taken, or within a few days of starting therapy.[39] In February 2008, the Australian Therapeutic Goods Administration attached a boxed warning concerning this adverse effect.[40]
Rodent studies of the tolerance-inducing properties have shown that zolpidem has less tolerance-producing potential than benzodiazepines, but in primates, the tolerance-producing potential of zolpidem was the same as seen with benzodiazepines.[46]
Zolpidem may be quantitated in blood or plasma to confirm a diagnosis of poisoning in people who are hospitalized, to provide evidence in an impaired driving arrest, or to assist in a medicolegal death investigation. Blood or plasma zolpidem concentrations are usually in a range of 30–300μg/L in persons receiving the drug therapeutically, 100–700μg/L in those arrested for impaired driving, and 1000–7000μg/L in victims of acute overdosage. Analytical techniques, in general, involve gas or liquidchromatography.[47][48][49]
Pharmacology
Mechanism of action
Zolpidem is a ligand of high-affinity positive modulator sites of GABAA receptors, which enhances GABAergic inhibition of neurotransmission in the central nervous system. It selectively binds to α1subunits of this pentamericion channel. Accordingly, it has strong hypnotic properties and weak anxiolytic, myorelaxant, and anticonvulsant properties.[9] Opposed to diazepam, zolpidem is able to bind to binary αβ GABA receptors, where it was shown to bind to the α1–α1 subunit interface.[50] Zolpidem has about 10-fold lower affinity for the α2- and α3- subunits than for α1, and no appreciable affinity for α5 subunit-containing receptors.[51][52] ω1 type GABAA receptors are the α1-containing GABAA receptors and are found primarily in the brain, the ω2 receptors are those that contain the α2-, α3-, α4-, α5-, or α6 subunits, and are found primarily in the spine. Thus, zolpidem favours binding to GABAA receptors located in the brain rather than the spine.[53] Zolpidem has no affinity for γ1 and γ3 subunit-containing receptors and, like the vast majority of benzodiazepine-like drugs, it lacks affinity for receptors containing α4 and α6.[54] Zolpidem modulates the receptor presumably by inducing a receptor conformation that enables an increased binding strength of the orthosteric agonist GABA towards its cognate receptor without affecting desensitization or peak currents.[55]
Microsome studies indicate zolpidem is metabolized by CYP3A4 (61%) CYP2C9 (22%), CYP1A2 (14%), CYP2D6 (<3%), and CYP2C19 (<3%).[15] Less than 1% is excreted in urine unchanged.[9] It is principally metabolized into three metabolites, none of which are believed to be pharmacologically active. The absolute bioavailability of zolpidem is about 70%. The drug reaches peak concentration in about 2 hours and has a half-life in healthy adults of about 2–3 hours.[11][9][12] Zolpidem's half life is decreased in children and increased in the elderly and people with liver issues. While some studies show men metabolize zolpidem faster than women (possibly due to testosterone),[58] others do not.[9] A review found only a 33% lower clearance in women compared to men, suggesting the FDA's dosage reduction of 50% for women may have been too large.[59]
Interactions
People should not consume alcohol while taking zolpidem, and should not be prescribed opioid drugs nor take such illicit drugs recreationally.[60] Use of opioids with zolpidem increases the risk of respiratory depression and death.[16] The U.S. Food and Drug Administration (FDA) is advising that the opioid addiction medications buprenorphine and methadone should not be withheld from patients taking benzodiazepines or other drugs that depress the central nervous system (CNS).[61]
Next day sedation can be worsened if people take zolpidem while they are also taking antipsychotics, other sedatives, anxiolytics, antidepressants, anticonvulsants, and antihistamines. Some people taking antidepressants have had visual hallucinations when they also took zolpidem.[16]
Cytochrome P450 inhibitors, particularly CYP3A4 and CYP1A2 inhibitors such as fluvoxamine, ciprofloxacin, and clarithromycin[62] will increase the effects of a given dose of zolpidem.[16] Cytochrome P450 activators like St. John's Wort may decrease the activity of zolpidem.[16] One study found that caffeine increases the concentration over time curve of zolpidem by about 20% and furthermore found that caffeine cannot adequately compensate for the impaired cognition caused by zolpidem.[63] Other studies show no effect of caffeine on zolpidem metabolism.[9]
Chemistry
Three chemical syntheses of zolpidem are common. 4-Methylacetophenone is used as a common precursor. This is brominated and reacted with 2-amino-5-methylpyridine to give the imidazopyridine. From here the reactions use a variety of reagents to complete the synthesis, either involving thionyl chloride or sodium cyanide. These reagents are challenging to handle and require thorough safety assessments.[64][65][66] Though such safety procedures are common in the industry, they make clandestine manufacture difficult.
Several major side-products of the sodium cyanide reaction have been characterised and include dimers and mannich products.[67]
Alpidem is also an imidazopyridine and is an analogue of zolpidem.[68][69][70] Both agents are GABAA receptor positive allosteric modulators.[68][69][70] However, whereas zolpidem is used as a hypnotic and sedative, alpidem was used as an anxiolytic.[68][69][70]
History
Zolpidem was used in Europe starting in 1988 and was brought to market there by Synthelabo.[71] Synthelabo and Searle collaborated to bring it to market in the US, and it was approved in the United States in 1992 under the brand name "Ambien".[71][21] It became available as a generic medication in 2007.[22]
In 2015, the American Geriatrics Society said that zolpidem, eszopiclone, and zaleplon met the Beers criteria and should be avoided in individuals 65 and over "because of their association with harms balanced with their minimal efficacy in treating insomnia."[33][34] The AGS stated the strength of the recommendation that older adults avoid zolpidem is "strong" and the quality of evidence supporting it is "moderate."[34]
Society and culture
Prescriptions in the US for all sleeping pills (including zolpidem) steadily declined from around 57 million tablets in 2013, to around 47 million in 2017, possibly due to concern about prescribing addictive drugs amid the opioid crisis.[72]
Military use
The United States Air Force uses zolpidem as one of the hypnotics approved as a "no-go pill" (with a six-hour restriction on subsequent flight operation) to help aviators and special duty personnel sleep in support of mission readiness. (The other hypnotics used are temazepam and zaleplon.) "Ground tests" are required before an authorization issued to use the medication in an operational situation.[73]
Recreational use
Zolpidem has potential for medical misuse when the drug is continued long term without or against medical advice, or for recreational use when the drug is taken to achieve a "high".[74][75] The transition from medical use of zolpidem to high-dose addiction or drug dependence can occur with use, but some believe it may be more likely when used without a clinical recommendation to continue using it, when physiological drug tolerance leads to higher doses than the usual 5mg or 10mg, when consumed through insufflation or injection, or when taken for purposes other than as a sleep aid.[74] Recreational use is more prevalent in those having been dependent on other drugs in the past, but tolerance and drug dependence can still sometimes occur in those without a history of drug dependence. Chronic users of high doses are more likely to develop physical dependence on the drug, which may cause severe withdrawal symptoms, including seizures if abrupt withdrawal from zolpidem occurs.[76]
Other drugs, including benzodiazepines and zopiclone, are also found in high numbers of suspected drugged drivers.[20] Many drivers have blood levels far exceeding the therapeutic dose range, suggesting a high degree of excessive-use potential for benzodiazepines, zolpidem, and zopiclone.[47] U.S. Congressman Patrick J. Kennedy says that he was using zolpidem (Ambien) and promethazine (Phenergan) when he was caught driving erratically at 3 a.m.[77] "I simply do not remember getting out of bed, being pulled over by the police, or being cited for three driving infractions," Kennedy said.
As of 2009[update], nonmedical use of zolpidem is common for some adolescents. Some users have reported decreased anxiety, mild euphoria, perceptual changes, visual distortions, and hallucinations.[78][79] Zolpidem was used by Australian Olympic swimmers at the London Olympics in 2012, leading to controversy.[80]
Regulation
For the stated reason of its potential for recreational use and dependence, zolpidem (along with the other benzodiazepine-like Z-drugs) is a schedule IV substance under the Controlled Substances Act in the US. The United States patent for zolpidem was held by the French pharmaceutical corporation Sanofi-Aventis.[81]
Use in crime
The Z-drugs, including zolpidem, have been used as date rape drugs.[20][82] Zolpidem is available legally by prescription, and broadly prescribed unlike other date rape drugs: gamma-hydroxybutyrate (GHB), which is used to treat narcolepsy, or flunitrazepam (Rohypnol), which is only prescribed as a second-line choice for insomnia.[83] Zolpidem can typically be detected in bodily fluids for 36 hours, though it may be possible to detect it by hair testing much later, which is due to the short elimination half-life of 2.5–3 hours.[20] This use of the drug was highlighted during proceedings against Darren Sharper, who was accused of using the tablets he was prescribed to facilitate a series of rapes.[83][84]
Sleepwalking
Zolpidem received widespread media coverage in Australia after the death of a student who fell 20 metres (66 ft) from the Sydney Harbour Bridge while under the influence of zolpidem.[85]
Brand names
As of September 2018, zolpidem is marketed under many brands.[1]
Research
While cases of zolpidem improving aphasia in people with stroke have been described, use for this purpose has unclear benefits.[86] Zolpidem has also been studied in persistent vegetative states with unclear effect.[87] A 2017 systematic review concluded that while there is preliminary evidence of benefit for treating disorders of movement and consciousness other than insomnia (including Parkinson's disease), more research is needed.[88]
Animal studies in FDA files for zolpidem showed a dose dependent increase in some types of tumors, although the studies were too small to reach statistical significance.[89] Some observational epidemiological studies have found a correlation between use of benzodiazepines and certain hypnotics including zolpidem and an increased risk of getting cancer, but others have found no correlation; a 2017 meta-analysis of such studies found a correlation, stating that use of hypnotics was associated with a 29% increased risk of cancer, and that "zolpidem use showed the strongest risk of cancer" with an estimated 34% increased risk, but noted that the results were tentative because some of the studies failed to control for confounders like cigarette smoking and alcohol use, and some of the studies analyzed were case–controls, which are more prone to some forms of bias.[90] Similarly, a meta-analysis of benzodiazepine drugs also shows their use is associated with increased risk of cancer.[91]
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