Lunesta History and Development

From Zopiclone to Eszopiclone: The Chiral Switch

Racemic zopiclone entered clinical use in France in 1986 under the brand name Imovane and quickly spread to more than 80 countries. The United States never approved the racemate. Sepracor Inc., a Marlborough, Massachusetts company focused on chiral chemistry, recognized that zopiclone existed as two mirror-image molecules: the S-enantiomer and the R-enantiomer.

Preclinical binding assays demonstrated that the S-isomer possessed roughly 50-fold greater affinity for the GABA-A benzodiazepine binding site compared to the R-isomer [1]. This pharmacological asymmetry made an enantiomer-based development program commercially and scientifically rational. Sepracor filed its original patent for the isolated S-enantiomer in 1997 and began Phase I trials in 1999.

The strategy was not unique to sleep medicine. "Chiral switches" also produced esomeprazole from omeprazole and escitalopram from citalopram during the same era. What distinguished eszopiclone was that racemic zopiclone had never received U.S. marketing authorization, so the FDA evaluated eszopiclone purely on its own merit rather than as a reformulation of an existing American product.

Mechanism of Action: How Eszopiclone Works

Eszopiclone binds as a positive allosteric modulator at the gamma-aminobutyric acid type A (GABA-A) receptor complex. Its binding site overlaps with, but is not identical to, the classical benzodiazepine binding pocket on the alpha-1 subunit interface [2]. The result is enhanced chloride ion conductance, neuronal hyperpolarization, and reduced cortical arousal.

Selectivity matters here. Benzodiazepines bind nonselectively across alpha-1, alpha-2, alpha-3, and alpha-5 subunit-containing receptors. Eszopiclone shows preferential activity at alpha-2 and alpha-3 subunit-containing GABA-A receptors relative to older benzodiazepines, which may contribute to its lower propensity for next-day motor impairment at therapeutic doses [3]. Alpha-1 activity still mediates sedation, but the proportional reduction in alpha-1 contribution relative to a full benzodiazepine agonist is thought to explain the more favorable cognitive side-effect profile observed in clinical trials.

Peak plasma concentration occurs approximately 1 hour after oral dosing. The elimination half-life is 6 hours in healthy adults, considerably longer than zaleplon (1 hour) and somewhat longer than zolpidem immediate-release (2.5 hours) [4]. This pharmacokinetic profile supports both sleep-onset and sleep-maintenance efficacy, a dual benefit confirmed in polysomnographic studies.

The Registration Program: Key Clinical Trials

Sepracor's Phase III program included both short-term (2-week, 6-week) and long-term (6-month) randomized controlled trials, an unusually strong dataset for the hypnotic class at the time.

The 6-Month Krystal Study

The most influential trial was conducted by Andrew Krystal and colleagues and published in Sleep in 2003 [5]. This was a double-blind, placebo-controlled, parallel-group study enrolling 788 adults with chronic primary insomnia across 50 U.S. sites. Patients received eszopiclone 3 mg or placebo nightly for 6 months.

Results at month 6: eszopiclone reduced subjective sleep-onset latency by a mean of 25.1 minutes versus 13.8 minutes for placebo (P<0.001). Wake time after sleep onset decreased significantly. Patient-reported sleep quality scores improved by 44% over baseline compared to 31% for placebo. The separation from placebo was maintained at every monthly assessment without evidence of tolerance development.

This was the first controlled demonstration that a sedative-hypnotic could maintain efficacy over 6 months without dose escalation, directly contradicting prevailing assumptions about inevitable tolerance to hypnotic agents.

Short-Term Polysomnographic Trials

A separate 44-night PSG study by Zammit et al. (2004) confirmed objective findings: eszopiclone 3 mg reduced latency to persistent sleep by 17.1 minutes versus placebo and increased total sleep time by 36 minutes (P<0.001) [6]. These objective polysomnographic data supported the subjective reports from the larger Krystal trial.

Elderly Population Trials

Because insomnia prevalence increases with age and older adults metabolize drugs more slowly, Sepracor conducted a dedicated trial in patients aged 65 to 86. Scharf et al. (2005) randomized 231 elderly patients to eszopiclone 2 mg or placebo for 2 weeks [7]. Sleep latency decreased and sleep efficiency improved significantly. Based partly on these data, the approved starting dose for elderly patients was set at 1 mg.

FDA Approval and Labeling: December 2004

The FDA approved eszopiclone on December 15, 2004, under NDA 021476 [8]. The approval carried no restriction on treatment duration, making eszopiclone the first U.S. hypnotic whose labeling did not include a "short-term use only" limitation. Earlier hypnotics (zolpidem, zaleplon, triazolam) were labeled for 7 to 10 days of use, largely because supporting data beyond that timeframe did not exist.

The decision rested on the 6-month Krystal dataset combined with an additional 12-month open-label safety extension in which 471 patients maintained response without dose escalation [5]. The advisory committee voted in favor of approval, and the FDA agreed that the chronic-use data warranted broader labeling.

Initial approved doses were 2 mg and 3 mg for adults and 1 mg and 2 mg for elderly patients. In 2014, the FDA added a recommendation to start all patients at 1 mg based on post-marketing next-day impairment reports, similar to the dose reduction it required for zolpidem in 2013 [9].

Post-Marketing Evolution and Safety Updates

2013 to 2014: Dose Reduction Guidance

Following a broader FDA review of all sedative-hypnotic agents and driving impairment data, the agency issued a safety communication in May 2014 recommending that prescribers start eszopiclone at 1 mg in all adults. Blood-level simulations indicated that some patients, particularly women and those with hepatic impairment, carried plasma concentrations above the impairment threshold 8 hours after a 3 mg dose.

2019: Boxed Warning for Complex Sleep Behaviors

In April 2019, the FDA mandated a boxed warning for eszopiclone (along with zolpidem and zaleplon) regarding rare but serious complex sleep behaviors including sleepwalking, sleep-driving, and engaging in activities while not fully awake [10]. The agency identified 66 cases of serious injury or death associated with these behaviors across the entire sedative-hypnotic class over 26 years of post-marketing surveillance. Eszopiclone is now contraindicated in patients with a history of a complex sleep behavior episode on any sedative-hypnotic.

Generic Entry: 2014

Sepracor (renamed Sunovion in 2010 after its acquisition by Dainippon Sumitomo Pharma) lost market exclusivity in 2014. Multiple generic manufacturers entered the market. By 2016, generic eszopiclone accounted for over 90% of U.S. prescriptions for the molecule. Annual prescription volume for eszopiclone peaked at approximately 11 million in 2012 and declined to roughly 4.5 million by 2022 as competing options expanded [11].

Eszopiclone in Context: The Non-Benzodiazepine Generation

Eszopiclone arrived as the third "Z-drug" approved in the United States, following zolpidem (1992) and zaleplon (1999). Each occupies a different pharmacokinetic niche.

Zaleplon's 1-hour half-life restricts its utility to pure sleep-onset insomnia. Zolpidem immediate-release at 2.5 hours works for onset but offers limited maintenance benefit. Zolpidem extended-release (Ambien CR, approved 2005) addressed maintenance but still carried a 2.8-hour half-life for the immediate component. Eszopiclone's 6-hour half-life covers both onset and maintenance without requiring a modified-release formulation.

The American Academy of Sleep Medicine's 2017 clinical practice guideline conditionally recommended eszopiclone for both sleep-onset and sleep-maintenance insomnia, citing moderate-quality evidence for patient-important outcomes [12]. The recommendation placed eszopiclone alongside suvorexant and doxepin as agents with maintenance data, while zolpidem and zaleplon received recommendations only for sleep-onset difficulty.

Corporate History: From Sepracor to Sunovion

Sepracor Inc. was founded in 1984 with a business model centered on chiral purification of existing racemates. Eszopiclone became the company's first major commercial success. Lunesta launch-year sales in 2005 reached $691 million, a figure that exceeded analyst expectations.

In 2009, Dainippon Sumitomo Pharma acquired Sepracor for $2.6 billion. The company was renamed Sunovion Pharmaceuticals in 2010. Sunovion continued to market branded Lunesta until patent expiration and shifted its neuroscience pipeline toward latuda (lurasidone) for bipolar depression and schizophrenia. The eszopiclone franchise generated cumulative U.S. branded sales exceeding $8 billion between 2005 and 2014.

Current Place in Therapy

Current guidelines from the American College of Physicians (2016) recommend cognitive behavioral therapy for insomnia (CBT-I) as first-line treatment, with pharmacotherapy reserved for patients who do not respond adequately [13]. When medication is chosen, eszopiclone remains a standard option, particularly for patients with both sleep-onset and sleep-maintenance complaints who require treatment beyond the short term.

The 2023 European Insomnia Guideline from the European Sleep Research Society similarly positions non-benzodiazepine receptor agonists including eszopiclone (or zopiclone in European markets) as second-line agents after CBT-I, with orexin receptor antagonists (suvorexant, lemborexant) as alternatives [14].

Eszopiclone is prescribed at a starting dose of 1 mg at bedtime, with titration to 2 mg or 3 mg based on response and tolerability, and 2 mg maximum in patients aged 65 and older or those with severe hepatic impairment.