How an Understanding of the Function of the Locus Coeruleus Led to Use of Dexmedetomidine to Treat Agitation in Bipolar Disorder: Example of Rational Development of Psychiatric Medications

Improving the pharmacotherapeutic treatment of agitation associated with bipolar disorder

INTRODUCTION

Agitation is commonly encountered in people with bipolar disorder, particularly when experiencing a manic episode. The number of approved pharmacological agents to manage acute episodes of agitation in this population is limited.

AREAS COVERED

A search was conducted using the US National Library of Medicine PubMed.gov resource for English-language papers of clinical trials and reviews/meta-analyses, using the text words 'bipolar disorder' AND 'agitation,' as well as any papers with both two text words in the title, without any date restrictions.

EXPERT OPINION

Existing pharmacologic options approved by regulatory authorities for the treatment of acute episodes of agitation associated with bipolar disorder have similar degrees of efficacy but differ in their tolerability profiles and ease of use, giving clinicians an opportunity to individualize treatment. The goal is to treat mild-moderate agitation before it evolves into severe agitation, encouraging noninvasive pharmacologic treatment options. Inhaled loxapine and sublingual dexmedetomidine are newer options with rapid onset of action and may be preferable for patients willing to cooperate with treatment.

Seven Mechanistically Different Classes of Medications Can Be Used to Treat Insomnia and Related Sleep Disorders

This column reviews the neurobiology of the sleep-wake cycle as it is currently known, the 7 classes of currently available sleep-enhancing medications, and how their mechanisms of action relate to the neurobiology of sleep. Clinicians can use this information to select medications for their patients, which is particularly important because some patients respond to some of these medications but not others, or tolerate some but not others. This knowledge can also help the clinician switch among classes when a medication that was initially efficacious begins to fail a patient. It can also prevent the clinician from cycling through all of the members of a single medication class. Such a strategy is unlikely to be helpful for a patient except in the situation in which pharmacokinetic differences among members of the medication class result in some agents in that class being helpful for a patient who has either a delayed onset of action or undesirable carry-over effects with other agents in that class. An understanding of the classes of sleep-enhancing medications highlights the importance of knowing the neurobiology that underlies a psychiatric illness. The activity of a number of neurobiological circuits, such as the one reviewed in this column, has now been well established, while work to understand others is still at a much earlier stage. Psychiatrists who gain an understanding of such circuits will be better able to provide effective care for their patients.

Sublingual dexmedetomidine: repurposing an anesthetic as an anti-agitation agent

INTRODUCTION

Especially when acutely ill, individuals with schizophrenia and bipolar disorder can present with agitated behavior. The initial approach to agitation management are non-pharmacologic strategies such as verbal de-escalation techniques; however, pharmacologic interventions may be needed. Dexmedetomidine is a selective alpha-2 adrenergic receptor agonist, and a sublingual formulation has been approved in the US for the treatment of agitation associated with schizophrenia and bipolar disorder in adults.

AREAS COVERED

The authors review the published literature on sublingual dexmedetomidine using the US National Library of Medicine's PubMed.gov resource. Pharmacodynamics, pharmacokinetics, and efficacy and tolerability findings are summarized. The authors also provide a discussion to its potential place in the treatment armamentarium.

EXPERT OPINION

Sublingual dexmedetomidine is an effective and well-tolerated pharmacologic option for the treatment of agitation associated with schizophrenia and bipolar disorder. The sublingual method of administration allows for a rapid onset of action with treatment effects beginning as early as 20 minutes after administration. Adverse effects include somnolence, hypotension, oral paresthesia, hypoesthesia, and dry mouth. Further study will be needed to evaluate sublingual dexmedetomidine in real-world patients receiving concomitant psychotropic medications.

Treatment of Agitation in Individuals With Bipolar Disorder or Schizophrenia: Lessons Learned for Clinical Psychiatry and Psychiatric Drug Development

Six lessons can be learned from the pivotal registration trials for sublingual dexmedetomidine (SLD) for the treatment of agitation in individuals with bipolar disorder or schizophrenia: (1) Knowing the function of a well-defined circuit in the brain, such as the locus coeruleus (LC), facilitates the development of central nervous system drugs. (2) Agitation can be conceptualized both clinically and physiologically. From both perspectives, agitation can present and escalate along a spectrum from mild, characterized as mainly hyperaroused (possibly only a subjective experience with no observable manifestations in its mildest form), to moderate to severe. In the severe state, the patient poses a potential danger to self and others. The level of agitation a patient is experiencing can determine the most appropriate treatment. Behavioral techniques may be sufficient for the mild state. As agitation progresses beyond mild severity, medication intervention becomes needed. SLD can be effective when agitation is moderate or even more severe. At this stage, patients can recognize and be distressed by their symptoms and participate in treatment. When agitation has escalated to such a severe state that patients can no longer participate in treatment, then intramuscular or intravenous medication may be needed. In quite severe cases, physical restraint as well as medication may be required. The Positive and Negative Syndrome Scale-Excited Component (PANSS-EC or PEC), a subscale of the PANSS, is a helpful instrument to assess where an individual is along the agitation spectrum. The PEC has been used in studies of pharmacological treatments for agitation, and it is accepted by the US Food and Drug Administration as the primary rating instrument in pivotal efficacy studies of treatments for agitation. (3) Where the patient is on the agitation spectrum is a function of the activity of the LC, which can be one factor in determining the SLD dose that will optimize the patient's clinical outcome. Clinical outcome is optimized when complete resolution of agitation is rapidly achieved, and adverse effects either do not occur or are not clinically meaningful. The adverse effects of greatest interest with SLD are decreases in resting systolic and diastolic blood pressures, reductions in these blood pressures under orthostatic stress, and lower resting heart rate. (4) To ensure safety, the subjects in 2 healthy volunteer studies were not administered doses equivalent to those used to treat agitated patients. The highest dose which a healthy volunteer tolerated in those studies was 40 µg. Agitated patients were treated with 120 and 180 µg doses. Thus the difference in doses was 3- to 4.5-fold. Agitated patients could also receive 2 additional half doses with an interval of 2 hours between the first and second administrations. For context, there are other examples of situations in which the dose of a drug that is well tolerated by healthy volunteers is lower than the dose that is well tolerated by patients. For example, it has long been accepted that patients with an acute relapse of schizophrenia can tolerate and need higher doses of D2 antagonists for efficacy than healthy volunteers can tolerate who will generally experience substantial sedation if given what is a clinically effective dose in such patients. (5) Agitation is a state phenomenon that may not recur when it is effectively treated, so that the treatment effect can persist for 24 hours despite the plasma half-life of the drug being 2 to 3 hours. (6) Given the established function of the LC, the fact that the dose response and the time curve of the effect are virtually identical in agitated individuals with bipolar disorder or schizophrenia supports the conclusion that the drug is not treating the syndromic diagnoses of bipolar disorder and schizophrenia but rather the state of being agitated because of overactivity of the LC. These 6 lessons are consistent with the discussions in numerous earlier columns in this series and are critical for both the practice of clinical psychopharmacology and psychiatric drug development.