Chapter 26

Prescription antidepressants and anxiolytic drugs routinely rank among the most commonly prescribed agents in the United States. Additionally, they are commonly used in veterinary medicine for a variety of behavioral disorders including separation anxiety, storm phobias, inappropriate urine marking, stereotypic behaviors, and psychogenic alopecia (see Chapter 117). Although mild adverse effects may be noted at therapeutic doses, severe toxicosis and death may result following overdose, especially if these drugs are ingested with other drugs with serotonergic properties (such as monoamine oxidase inhibitors or 5-hydroxytryptophan). Because of their frequent use, the palatability of some flavored veterinary formulations, and the potential for severe intoxication, unintentional overdoses of antidepressants rank among the most commonly reported cases to Pet Poison Helpline.

Antidepressants and anxiolytics encompass several drug classes, the most common of which include selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), benzodiazepines (BZDs), and nonbenzodiazepine (non-BZD) hypnotic agents. The pharmacologic and pharmacokinetic properties of these different classes vary greatly and account for a wide range of toxicities and mechanisms of action. Although some drugs, such as many SSRIs or TCAs, may cause severe intoxication in smaller dosages, others, such as BZDs, have a wider margin of safety and are less likely to result in severe toxicosis or death. Thus obtaining the exact name of the medication ingested by the pet is crucial to determine a proper course of treatment and guide prognosis. Due to the wide variability in clinical signs and treatments available for these drugs, along with the potential for severe intoxication, consultation with an animal poison control center is recommended (see Chapters 20 and Web Chapter 9).