Chapter 15: Drug Therapy of Depression and Anxiety Disorders

INTRODUCTION

Depression and anxiety disorders are the most common mental illnesses, each affecting in excess of 10-15% of the population at some time in their lives. With the advent of more selective and safer drugs, the use of antidepressants and anxiolytics has moved from the domain of psychiatry to other medical specialties, including primary care. The relative safety of the majority of commonly used antidepressants and anxiolytics notwithstanding, their optimal use requires a clear understanding of their mechanisms of action, pharmacokinetics, potential drug interactions, and the differential diagnosis of psychiatric illnesses.

A confluence of symptoms of depression and anxiety may affect an individual patient; some of the drugs discussed here are effective in treating both disorders, suggesting common underlying mechanisms of pathophysiology and response to pharmacotherapy. In large measure, our current understanding of pathophysiological mechanisms underlying depression and anxiety has been inferred from the mechanisms of action of psychopharmacological compounds (see Chapter 14). While depression and anxiety disorders comprise a wide range of symptoms, including changes in mood, behavior, somatic function, and cognition, some progress has been made in developing animal models that respond with some sensitivity and selectivity to antidepressant or anxiolytic drugs. The last half century has seen notable advances in the discovery and development of drugs for treating depression and anxiety.

CHARACTERIZATION OF DEPRESSIVE AND ANXIETY DISORDER

SYMPTOMS OF DEPRESSION

Depression is classified as major depression (i.e., unipolar depression) or bipolar depression (i.e., manic depressive illness); bipolar depression and its treatment are discussed in Chapter 16. Lifetime risk of unipolar depression is ~15%. Females are affected twice as frequently as males. Depressive episodes are characterized by sad mood, pessimistic worry, diminished interest in normal activities, mental slowing and poor concentration, insomnia or increased sleep, significant weight loss or gain due to altered eating and activity patterns, psychomotor agitation or retardation, feelings of guilt and worthlessness, decreased energy and libido, and suicidal ideation, occurring most days for a period of at least 2 weeks. In some cases, the primary complaint of patients involves somatic pain or other physical symptoms and can present a diagnostic challenge for primary care physicians. Depressive symptoms also can occur secondary to other illnesses such as hypothyroidism, Parkinson disease, and inflammatory conditions. Further, depression often complicates the management of other medical conditions (e.g., severe trauma, cancer, diabetes, and cardiovascular disease, especially myocardial infarction).

Depression is underdiagnosed and undertreated. Approximately 10-15% of those with severe depression attempt suicide at some time. Thus, it is important that symptoms of depression be recognized and treated in a timely manner. Furthermore, the response to treatment must be assessed and decisions made regarding continued treatment with the initial drug, dose adjustment, adjunctive therapy, or alternative medication.