Hypnotic use for insomnia management in chronic obstructive pulmonary disease

1. Introduction 

Chronic Obstructive Pulmonary Disease (COPD) encompasses a range of respiratory diseases including chronic bronchitis, emphysema, and others. The disease is defined as a progressive limitation of functional airflow that is not fully reversible with inhaled bronchodilators [1]. The disease is progressive and chronic, requiring long-term treatment to improve quality of life in affected patients.

Several comorbidities accompany COPD including unexplained weight loss, cardiovascular disease, peripheral muscle weakness, cognitive impairment, depression, anxiety, and sleep disorders [2], [3]. COPD patients are more likely to have difficulty falling and staying asleep and have increased sleepiness during the day. In some cases, they take hypnotics to combat their sleep disturbance. Arousals from sleep are more likely in these patients due to chronic coughing and nocturnal wheezing and also nocturnal oxygen desaturation [4]. In addition, an increased number of COPD patients also have obstructive sleep apnea syndrome (OSAS), a condition that is referred to as overlap syndrome [5]. The coincidence of OSAS has detrimental effects on respiratory physiology and exacerbates hypoxia and hypercapnia in COPD patients during sleep [6]. This is particularly important to recognize because hypoxia correlates strongly with nocturnal mortality [7].

The most common pharmacologic treatment prescribed for insomnia including those comorbid with COPD are the benzodiazepine receptor agonists (BZRAs), a group of drugs that function by binding to the benzodiazepine receptor at the GABAA complex. These receptors are expressed in the plasma membrane of neurons throughout the CNS and PNS [8]. BZRAs include both the traditional benzodiazepines, which bind a broad range of BZ receptors and a newer group of more selective BZRAs called the non-benzodiazepine BZRAs. These drugs are more selective to a BZ receptor subtype that is expressed in the CNS and people have hypothesized that they produce fewer adverse side effects on pulmonary function than do the traditional BZRAs [8]. The selective MT1/MT2 melatonin receptor agonist ramelteon is another option for the treatment of insomnia. Melatonin receptors, expressed in the hypothalamus, regulate neural and endocrine mediated processes that control mammalian circadian rhythms [9]. By engaging signaling pathways downstream of these G-protein coupled receptors, ramelteon is believed to decrease sleep latency and increase sleep efficiency. Finally, the antidepressant trazodone is sometimes used off-label for treatment of insomnia and may be considered for use in COPD patients, although there is a lack of data on its effectiveness and safety in this patient population (NIH consensus statement).

It has become clear that the COPD patient population comorbid for insomnia is underserved by current practices in sedative pharmacotherapy. The current treatment paradigm relies heavily on CNS depressants, namely benzodiazepines, that can lead to hypoxia [4]. While there are no pharmacological treatments specifically indicated for the treatment of sleep disturbances in the COPD population, evidence suggests a reevaluation of the current treatment paradigm for this cohort of patients. As our understanding of sleep mechanisms has increased, so too has our appreciation for the clinical potential associated with newer sleep therapies. This review will discuss the clinical impact of insomnia on the COPD population and will highlight special considerations to be taken for this population and the risks related to current pharmacological treatment options of insomnia in COPD.

2. Effects of sleep on respiratory function in the COPD population 

During sleep, a number of respiratory functions are affected in normal healthy individuals, including alterations in central respiratory control, airway resistance and airway muscle tone. Overall, these effects result in hypoventilation, moderate hypercapnia, and hypoxia [10]. During sleep the response of the respiratory center in the brain to both hypoxia and hypercapnia is attenuated, particularly during phasic REM sleep [11], [12], [13]. The changes in arterial blood gases that occur in normal subjects during sleep are exacerbated in patients with COPD. Moreover, sleep related breathing disorders occur with relatively high frequency in this population, further worsening sleep-related hypoxia and hypercapnia, particularly during REM sleep [14]. These alterations in COPD patients may contribute to an increased frequency of nocturnal awakenings. In addition, these effects of sleep on blood gas levels should be taken into consideration when choosing hypnotic treatment for insomnia, as those that promote further alterations may be particularly dangerous in this patient population.

Patients with COPD have varied levels of alterations in arterial blood gas values during wakefulness. Those that exhibit even mildly hypoxic diurnal arterial oxygen tension (PaO2) levels tend to develop substantial nocturnal oxygen desaturation, especially during REM sleep [14]. Studies have recognized that the hypoventilation that occurs during sleep is the major cause of nocturnal oxygen desaturation among COPD patients [4], [15], [16]. Furthermore, the changes in respiratory muscle function that occur during sleep, worsen functional residual capacity and contribute to lower ventilation/perfusion matching, exacerbating desaturation [17], [18]. Nocturnal PaO2 tends to be lower in COPD patients relative to normal subjects since the PaO2 drops observed normally during sleep cause a larger drop in saturation when the patient is already hypoxemic, following the steepness of the oxyhemoglobin dissociation curve [3], [19].

Obstructive Sleep Apnea Syndrome (OSAS), relatively common in individuals over the age of 45, occurs in about 10–15% of patients with COPD, a condition referred to as “Overlap Syndrome” [20]. Individuals with both conditions tend to develop dangerously low levels of PaO2 which is believed to occur because COPD patients are already hypoxemic at the beginning of each apneic event [20], [21], [22]. Alterations in arterial blood gas values in individuals with Overlap Syndrome lead to pulmonary hypertension which is associated with increased risk of cardiac arrhythmias and cor-pulmonale. These patients have a decreased survival rate over 5 years relative to patients that have OSAS alone [23].

3. Insomnia in the COPD population 

Nocturnal hypoxia and hypercapnia cause increased arousals and sleep disruption in COPD patients to improve respiration. This leads to sleep disruption and, in vulnerable individuals, chronic insomnia [3]. Over 50% of COPD patients report a long sleep latency, frequent arousals during the night and/or general insomnia [8]. Insomnia tends to be more prevalent and severe with advanced disease, roughly correlating with the extent of underlying lung disease [24]. Analysis of a large COPD database revealed that 21.4% of the listed COPD patients were diagnosed with and were treated for insomnia as compared to only 7.2% of non-COPD patients [25].

4. The effects of COPD treatment on the development of insomnia 

Although few studies have been done to determine the role that drugs used to treat COPD have on sleep, it is clear that insomnia can be a side effect of some of these medications. For example, bronchodilators used to treat some COPD patients have been noted to cause insomnia in a small population of treated patients [26], [27], [28]. In addition, other medications commonly prescribed to COPD patients including corticosteroids and β-adrenoreceptor agonists contribute to insomnia [29]. In contrast, nocturnal oxygen therapy has been shown to improve sleeplessness in COPD patients, perhaps by preventing awakenings due to oxygen desaturation during the night [30]. There is a lack of studies done to determine whether or not expectorants have any impact on the quality of sleep in COPD patients.

5. Pharmacologic treatment of insomnia 

There are currently a limited number of classes of medication that are used to treat insomnia (Table 1). Benzodiazepine receptor agonists (BZRAs) are the most commonly prescribed sleep agents used in the management of insomnia in the COPD population [8], [31], [32]. This class of drugs includes both the traditional benzodiazepines that share the formal benzodiazepine chemical structure and have affinities for multiple subtypes of BZ receptors as well as the newer non-benzodiazepines (zolpidem, eszopiclone, and zaleplon), that have a higher selectivity for a narrower range of BZ receptor subtypes [33]. Another treatment option for insomnia in COPD patients is ramelteon, a MT1/MT2 melatonin receptor agonist [9]. In clinical trails, ramelteon has been shown to be safe in patients with mild-to-moderate COPD and in mild-to-moderate OSAS patients [34], [35]. Finally, low dose sedating antidepressants such as trazodone have been used as an off-label treatment of insomnia. However, it is not clearly understood at what doses these drugs promote sleep and the safety of these doses. Clinical studies have found this agent to be safe in not exacerbating respiratory function in COPD patients, but there is no data on dose related safety and efficacy in subjects not suffering from depression [31], [32], [36].

Table 1. Pharmacologic options for treatment of insomnia

	Drug classification	Drug subclass	Drug(s) (half-life)	Receptor	Mechanism of sedation
	BZRAa	Benzodiazepines	Lorazepam (10–12h)	BZ1, BZ2, BZ3, BZ5	Neuron desensitization, CNS depression, smooth muscle relaxation, anxiolytic effects
			Temazepam (8–20h)
			Triazolam (2h)
			Flurazepam (>40h)
			Estazolam (10–24h)
			Quazepam (25–100h)
	BZRAa	Non-benzodiazepines	Zopliclone (5–6h)	BZ1,3	Neuron desensitization, CNS depression
			Eszopliclone (5–6h)
			Zolpidem (2h)
			Zaleplon (2h)
	Antidepressants	Serotonin reuptake receptor antagonist	Trazodone (3–6h)	5HT2A serotonin receptors	Unknown, may indirectly ↑ GABA levels
	Melatonin receptor agonists	Selective MT1/MT2 receptor agonist	Ramelteon (1–2h)	MT1/MT2	Blocks circadian alerting signals in the hypothalamus

a Benzodiazepine receptor agonist.

6. Complications associated with the use of standard insomnia treatment 

6.2. Non-benzodiazepine BZRAs 

A newer generation of BZ receptor agonists, also known as non-benzodiazepines, has a higher selectivity for BZ receptor subtypes expressed predominantly in neurons of the CNS (Table 1). These drugs have little to no affinity for the other GABAA receptor subtypes, and have fewer adverse effects on respiratory function than do the traditional benzodiazepines. Furthermore, these drugs specifically target the receptor believed to mediate the sedation effects of the BZRAs [45]. Drugs in this subclass include zolpidem, zolpdem CR, zopiclone and its active racemate eszopiclone, and zaleplon (Table 1). While zolpidem and zaleplon show selectivity for the BZ alpha 1 subunit, zopiclone and eszopiclone are selective for the alpha 3 subunit.

The non-benzodiazepine BZRAs have similar effects on sleep latency and efficiency as traditional benzodiazepines (Table 2) [33]. Several clinical studies have been conducted to test the effects of these drugs on pulmonary function. Unlike benzodiazepines, zopiclone (7.5–10mg) and zolpidem (10mg) have been found to have no significant effect on ventilatory drive and central control of breathing in normal subjects or in patients with mild to moderate COPD [39], [46], [47], [48]. One small study has noted a non-significant trend towards an increased number and duration of apneic spells in patients taking 5–10mg zopiclone [49].

Table 2. Known adverse effects of current pharmaceuticals on respiratory function in COPD patients

	Drug subclass	Effects on sleep	Adverse pulmonary effects in COPD patients	References
	Benzodiazepines	↓ sleep latency, ↑ sleep efficiency, ↓ arousals	↓ tidal volume, ↓ arousal response to hypercapnia, ↑ hypoxia, ↑ hypercapnia	[37], [38], [39]
	Non-benzodiazepines	↓ sleep latency, ↑ sleep efficiency, ↓ arousals	↑ apneasa	[49]
	Melatonin receptor agonists (ramelteon)	↓ sleep latency, ↑ sleep efficiency	No effect on apnea or PaO2a	[56]
	Trazodone	↑ sleep efficiency (only in patients with depression)	Unknowna	[58]

a Further research is needed.

Furthermore, non-benzodiazepine BZRAs have amnestic and cognitive effects similar to benzodiazepines. A recent review reported sixteen studies that included 1541 participants that evaluated the differences between benzodiazepines and non-benzodiazepines in terms of cognitive and psychomotor adverse events in elderly patients over the age of 60 years, finding no significant differences between treatments [50]. Thus, although non-benzodiazepines have fewer apparent adverse effects on pulmonary function, the potential for adverse effects on cognitive function may complicate treatment of insomnia in COPD patients, many of whom suffer from cognitive impairment or are elderly patients at risk for fall-related fractures [51].

7. Conclusion 

COPD is a leading cause of worldwide mortality. Managing quality of life in COPD patients is critical as they are likely to live with the disease as it progresses over significant periods of time. Among other comorbidities, insomnia is prevalent in the COPD population and affected individuals seek treatment to improve their quality of sleep. Additionally, a significant percentage of COPD patients also have OSAS, which further complicates treatment of sleep disorders in the COPD population [4], [20], [22]. The natural drops in minute ventilation, tidal volume and functional residual capacity, coupled with the increased airway resistance and respiratory muscle atonia that occur normally during sleep, exacerbate the hypoxia and hypercapnia seen in COPD, producing nocturnal oxygen desaturation in this population [17], [60]. These changes in arterial blood gases and reduced pulmonary muscle strength and endurance increase the risk of nocturnal mortality [14], [61].

Safe pharmacological treatment of insomnia must include consideration for whether the hypnotic could potentially exacerbate the already impaired gas exchange and atonia problems that present during sleep in COPD patients. Benzodiazepines are prescribed despite adverse pulmonary effects that could potentially lead to poor outcomes in the COPD population [8], [62]. Furthermore, the side effects of cognitive impairment and anterograde amnesia make benzodiazepines a poor choice for the elderly COPD population. These complications highlight the need to reevaluate the current insomnia treatment paradigm in the COPD population.

The non-benzodiazepine BZRAs may offer some benefit in comparison to traditional benzodiazepines with respect to respiratory depression complications. However, there is some data to suggest that these drugs may promote apnea, which is known to significantly exacerbate hypoxia in COPD patients. Both types of BZRAs have amnestic effects which may pose problems if prescribed in the elderly COPD population already predisposed to cognitive impairment [32], [63]. Ramelteon shows promise in the COPD patient suffering from insomnia. It has been determined to be safe and efficacious in mild to moderate COPD and OSAS patients, with no adverse effects on nocturnal arterial blood gases [34], [35], however more clinical research needs to be done with ramelteon in this population. Trazodone has been shown to be effective only in patients with depression and comorbid insomnia. In addition, there is little to no data on the effects of trazodone on pulmonary function or in patients with COPD and OSAS [36], [58], [59]. While evidence and opinion point to a reevaluation of traditional BZRA therapies in favor of newer agents for COPD comorbid with insomnia, more research is needed to determine the safest and most effective treatment strategies.