Zolpidem

Zolpidem (brand names Ambien, Ambien CR, Intermezzo, Stilnox, Stilnoct, Sublinox, Hypnogen, Lunata, Zonadin, Sanval, Zolsana and Zolfresh) is a prescription medication used for the treatment of insomnia and some brain disorders. It is a short-acting nonbenzodiazepine hypnotic of the imidazopyridine class that potentiates GABA, an inhibitory neurotransmitter, by binding to GABA_A receptors at the same location as benzodiazepines. It works quickly, usually within 15 minutes, and has a short half-life of two to three hours.

Zolpidem has not adequately demonstrated effectiveness in maintaining sleep, unless delivered in a controlled-release (CR) form. However, it is effective in initiating sleep. Its hypnotic effects are similar to those of the benzodiazepine class of drugs, but it is molecularly distinct from the classical benzodiazepine molecule and is classified as an imidazopyridine. Flumazenil, a benzodiazepine receptor antagonist, which is used for benzodiazepine overdose, can also reverse zolpidem's sedative/hypnotic and memory-impairing effects.

Zolpidem has slight muscle relaxant and anticonvulsant properties, but has not been approved for use in muscle relaxation or seizure prevention. This is because the dosage of drug needed to cause muscle relaxation is 10 times the sedating dose, and the dosage needed for preventing seizures is 20 times the sedating dose; high dosages are more likely to cause unpleasant side effects such as hallucinations and amnesia. Contrary to early studies, more recent research has indicated that zolpidem is in fact a potent anticonvulsant. The anticonvulsant effects are not realized until the normal dosage range has been surpassed (meaning sedation would still be a major side effect) but the threshold for this effect is now believed to be considerably lower than original estimates.

The United States patent for zolpidem was held by the French pharmaceutical corporation Sanofi-Aventis. On April 23, 2007, the U.S. Food and Drug Administration (FDA) approved 13 generic versions of zolpidem tartrate. Zolpidem is available from several generic manufacturers in the UK, as a generic from Sandoz in South Africa and TEVA in Israel, as well as from other manufacturers such as Ratiopharm and Takeda GmbH (both Germany).

On January 10, 2013, the Food and Drug Administration announced it is requiring the manufacturer of Ambien and Zolpimist to cut the recommended dosage for women in half, after laboratory studies showed that the medicines can leave patients drowsy in the morning and at risk for motor vehicle collisions. The FDA recommended that manufacturers extend the new dosage cuts to men as well, who process the drug at a faster rate; however, the reasons men and women metabolize the drugs at different rates are still unknown. In May 2013, the FDA approved label changes specifying new dosage recommendations for zolpidem products because of concerns regarding next-morning impairment.

Medical uses

Clinicians prescribe zolpidem for short-term (usually about two to six weeks) treatment of insomnia. Zolpidem addresses sleep-initiation problems, but is not effective in maintaining sleep. Also, a 2012 NIH study showed that zolpidem's effectiveness is nearly as much due to psychological effects as to the drug itself, so "increased attention should be directed at psychological intervention of insomnia."

Adverse effects

Side effects may include:

• Night eating syndrome (also commonly known as sleep-eating)
• Headaches (mostly withdrawal symptom)
• Nausea (mostly withdrawal symptom)
• Vomiting (mostly withdrawal symptom)
• Dizziness
• Anterograde amnesia
• Hallucinations, through all physical senses, of varying intensity
• Altered thought patterns
• Ataxia or poor motor coordination, difficulty maintaining balance
• Euphoria or dysphoria
• Impaired judgment and reasoning
• Uninhibited extroversion in social or interpersonal settings
• Increased impulsivity (mostly withdrawal symptom)
• When stopped, rebound insomnia may occur

Some users have reported unexplained sleepwalking while using zolpidem, as well as sleep driving, binge eating while asleep, and performing other daily tasks while sleeping. 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. Rare reports of sexual parasomnia episodes related to zolpidem intake have also been reported. Sleepwalkers can sometimes perform these tasks as normally as they might if they were awake.

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.

The Sydney Morning Herald in Australia in 2007 reported a man who fell 30 meters to his death from a high-rise unit balcony may have been sleepwalking under the influence of Stilnox. The coverage prompted over 40 readers to contact the newspaper with their own accounts of Stilnox-related automatism, and as of March 2007, the drug was under review by the Adverse Drug Reactions Advisory Committee.

In February 2008, the Australian Therapeutic Goods Administration attached a boxed warning to zolpidem, stating that "Zolpidem may be associated with potentially dangerous complex sleep-related behaviors that may include sleep walking, sleep driving, and other bizarre behaviours. Zolpidem is not to be taken with alcoholic beverages. Caution is needed with other CNS-depressant drugs. Limit use to four weeks maximum under close medical supervision." This report received widespread media coverage after the death of Australian student Mairead Costigan, who fell 20 m from the Sydney Harbour Bridge while under the influence of Stilnox.

Tolerance, dependence, and withdrawal

A review medical publication found long-term use of zolpidem is associated with drug tolerance, drug dependence, rebound insomnia, and CNS-related adverse effects. It was recommended that zolpidem be used for short periods of time using the lowest effective dose. Zolpidem 10 mg is effective in treating insomnia when used intermittently no fewer than three and no more than five pills per week for a period of 12 weeks. The 15-mg zolpidem dosage provided no clinical advantage over the 10-mg zolpidem dosage.

Nonpharmacological treatment options (e.g. cognitive behavioral therapy for insomnia), however, were found to have sustained improvements in sleep quality. Animal studies of the tolerance-inducing properties have shown that in rodents, zolpidem has less tolerance-producing potential than benzodiazepines, but in primates the tolerance-producing potential of zolpidem was the same as that of benzodiazepines. Tolerance to the effects of zolpidem can develop in some people in just a few weeks. Abrupt withdrawal may cause delirium, seizures, or other severe effects, especially if used for prolonged periods and at high dosages.

When drug tolerance and physical dependence to zolpidem has developed, treatment usually entails a gradual dose reduction over a period of months to minimise withdrawal symptoms, which can resemble those seen during benzodiazepine withdrawal. Failing that, an alternative method may be necessary for some patients, such as a switch to a benzodiazepine equivalent dose of a longer-acting benzodiazepine drug, such as diazepam or chlordiazepoxide, followed by a gradual reduction in dosage of the long-acting benzodiazepine. Sometimes for difficult-to-treat patients, an inpatient flumazenil rapid detoxification program can be used to detoxify from a zolpidem drug dependence or addiction.

Alcohol has cross tolerance with GABA_A receptor positive modulators such as the benzodiazepines and the nonbenzodiazepine drugs. For this reason, alcoholics or recovering alcoholics may be at increased risk of physical dependency on zolpidem. Also, alcoholics and drug abusers may be at increased risk of abusing and or becoming psychologically dependent on zolpidem. It should be avoided in those with a history of alcoholism, drug misuse, physical dependency, or psychological dependency on sedative-hypnotic drugs. Zolpidem has rarely been associated with drug-seeking behavior, the risk of which is amplified in patients with a history of drug or alcohol abuse.

Overdose

An overdose of zolpidem may cause excessive sedation, pin-point pupils, or depressed respiratory function, which may progress to coma, and possibly death. Combined with alcohol, opiates, or other CNS depressants, it may be even more likely to lead to fatal overdoses. Zolpidem overdosage can be treated with the benzodiazepine receptor antagonist flumazenil, which displaces zolpidem from its binding site on the benzodiazepine receptor to rapidly reverse the effects of the zolpidem.

Detection in body fluids

Zolpidem may be quantitated in blood or plasma to confirm a diagnosis of poisoning in hospitalized patients, 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 30â€"300 μg/l in persons receiving the drug therapeutically, 100â€"700 μg/l in those arrested for impaired driving, and 1000â€"7000 μg/l in victims of acute overdosage. Analytical techniques, in general, involve gas or liquid chromatography.

Special precautions

Driving

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. Studies showed that eight hours after a bedtime dose of 10 mg, 15% of women and 3% of men would have blood levels that produce impaired driving skills; for an extended-release dose of 12.5 mg, the risk increased to 33% and 25%, respectively. As a consequence, the FDA recommended the dose for women be reduced and that prescribers should consider lower doses for men.

Elderly

The elderly are more sensitive to the effects of hypnotics including zolpidem. Zolpidem causes an increased risk of falls and may induce adverse cognitive effects.

An extensive review of the medical literature regarding the management of insomnia and the elderly found that there is considerable evidence of the effectiveness and durability of nondrug treatments for insomnia in adults of all ages, and these interventions are underused. Compared with the benzodiazepines, the nonbenzodiazepine (including zolpidem) sedative-hypnotics appeared to offer few, if any, significant clinical advantages in efficacy or tolerability in elderly persons. Newer agents with novel mechanisms of action and improved safety profiles, such as the melatonin receptor agonists, were found to hold promise for the management of chronic insomnia in elderly people. Long-term use of sedative-hypnotics for insomnia lacks an evidence base and has traditionally been discouraged for reasons that include concerns about such potential adverse drug effects as cognitive impairment (anterograde amnesia), daytime sedation, motor incoordination, and increased risk of motor vehicle accidents and falls. In addition, the effectiveness and safety of long-term use of these agents remain to be determined. More research is needed to evaluate the long-term effects of treatment and the most appropriate management strategy for elderly persons with chronic insomnia.

Gastroesophageal reflux disease

Patients suffering from gastroesophageal reflux disease (GERD) had reflux events measured to be significantly longer when taking zolpidem than on placebo. The same trend was found for reflux events in patients without GERD. This is assumed to be due to suppression of arousal during the reflux event, which would normally result in a swallowing reflex to clear gastric acid from the esophagus. Patients with GERD experience significantly higher esophageal exposure to gastric acid, which increases the likelihood of their developing esophageal cancer.

Pregnancy

Zolpidem has been assigned to pregnancy category C by the FDA. Animal studies have revealed evidence of incomplete ossification and increased postimplantation fetal loss 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 in human pregnancy. In one case report, zolpidem was found in cord blood at delivery. Zolpidem is recommended for use during pregnancy only when benefits outweigh risks.

Mechanism of action

Zaleplon and zolpidem both are agonists at the GABA A α 1 subunit. Due to its selective binding, zolpidem has very weak anxiolytic, myorelaxant, and anticonvulsant properties but very strong hypnotic properties. Zolpidem binds with high affinity and acts as a full agonist at the α₁-containing GABA_A receptors, about 10-fold lower affinity for those containing the α₂- and α₃- GABA_A receptor subunits, and with no appreciable affinity for α₅ subunit-containing receptors. ω₁ type GABA_A receptors are the α₁-containing GABA_A receptors and ω₂ GABA_A receptors are the α₂-, α₃-, α₄-, α₅-, and α₆-containing GABA_A receptors. ω₁ GABA_A receptors are found primarily in the brain, whereas ω₂ receptors are found primarily in the spine. Thus, zolpidem has a preferential binding for the GABA_A-benzodiazepine receptor complex in the brain but a low affinity for the GABA_A-benzodiazepine receptor complex in the spine.

Like the vast majority of benzodiazepine-like molecules, zolpidem has no affinity for α₄ and α₆ subunit-containing receptors. Zolpidem positively modulates GABA_A receptors, it is presumed by increasing the GABA_A receptor complex's apparent affinity for GABA without affecting desensitization or peak current. Like zaleplon (Sonata), zolpidem may increase slow wave sleep but cause no effect on stage 2 sleep.

A meta-analysis of the randomised, controlled, clinical trials that compared benzodiazepines against nonbenzodiazepines such as zolpidem has shown few consistent differences between zolpidem and benzodiazepines in terms of sleep onset latency, total sleep duration, number of awakenings, quality of sleep, adverse events, tolerance, rebound insomnia, and daytime alertness.

Chemistry

Three 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. Though such safety procedures are common in industry, they make clandestine manufacture difficult.

A number of major side-products of the sodium cyanide reaction have been characterised and include dimers and mannich products.

Drug-drug interactions

Notable drug-drug interactions with the pharmacokinetics of zolpidem include chlorpromazine, fluconazole, imipramine, itraconazole, ketoconazole, rifampicin, and ritonavir. Interactions with carbamazepine and phenytoin can be expected based on their metabolic pathways, but have not yet been studied. There does not appear to be any interaction between zolpidem and cimetidine or ranitidine. However, it was noted in the same study that cimetidine did appear to prolong the hypnotic effects of Zolpidem beyond its typical 3 hour duration, which is indicative of some sort of metabolic interaction.

Usage

Zolpidem is one of the most common GABA-potentiating sleeping medications prescribed in the Netherlands, with a total of 582,660 prescriptions dispensed in 2008.

The United States Air Force uses zolpidem as one of the hypnotics approved as a "no-go pill" (with a 6-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 prior to authorization issued to use the medication in an operational situation.

Society and culture

Abuse

Zolpidem has a potential for either medical misuse when the drug is continued long term without or against medical advice or recreational use when the drug is taken to achieve a "high". The transition from medical use of zolpidem to high-dose addiction or drug dependence can occur when used without a doctor's recommendation to continue using it, when physiological drug tolerance leads to higher doses than the usual 5 mg or 10 mg, when consumed through inhalation or injection, or when taken for purposes other than as a sleep aid. Misuse 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.

One case history reported a woman detoxifying from a high dose of zolpidem experiencing a generalized seizure, with clinical withdrawal and dependence effects reported to be similar to the benzodiazepine withdrawal syndrome.

Other drugs, including the benzodiazepines and zopiclone, are also found in high numbers of suspected drugged drivers. Many drivers have blood levels far exceeding the therapeutic dose range suggesting a high degree of excessive-use potential for benzodiazepines, zolpidem and zopiclone. U.S. Congressman Patrick J. Kennedy says that he was using Zolpidem (Ambien) and Phenergan when caught driving erratically at 3AM. "I simply do not remember getting out of bed, being pulled over by the police, or being cited for three driving infractions," Kennedy said.

Nonmedical use of zolpidem is increasingly common in the U.S., Canada, and the UK. Recreational users report that resisting the drug's hypnotic effects can in some cases elicit vivid visuals and a body high. Some users have reported decreased anxiety, mild euphoria, perceptual changes, visual distortions, and hallucinations.

Regulation

Zolpidem, along with the other benzodiazepine-like Z-drugs is a Schedule IV controlled substance in the U.S., according to the Controlled Substances Act, given its potential for abuse and dependence.

Date rape drug

Zolpidem has become a leading date rape drug. Unlike Rohypnol ("roofies"), which was banned in 1996, zolpidem is available legally by prescription, and unlike gamma-hydroxybutyrate, which is used to treat a rare form of narcolepsy, zolpidem was prescribed 43.8 million times in the U.S. in 2012. It dissolves readily in liquids such as wine, and can typically be detected in bodily fluids for only 36 hours, though it may be possible to detect it by hair testing much later; this is due to the short elimination half-life of 2.5â€"3 hours. This application 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.

Research

Zolpidem may provide short-lasting but effective improvement in symptoms of aphasia present in some survivors of stroke. The mechanism for improvement in these cases remains unexplained and is the focus of current research by several groups, to explain how a drug that acts as a hypnotic-sedative in people with normal brain function, can increase speech ability in people recovering from severe brain injury. Use of zolpidem for this application remains experimental at this time, and is not officially approved by any pharmaceutical manufacturers of zolpidem or medical regulatory agencies worldwide.

Zolpidem is being studied to determine whether it causes improved responsiveness or regional cerebral perfusion in patients with persistent vegetative states.

References

Further reading

External links

Media related to Zolpidem at Wikimedia Commons