Mirtazapine toxicity in cats: retrospective study of 84 cases (2006–2011)

Abstract

Objectives Mirtazapine is commonly used in veterinary medicine at doses of 1.88 or 3.75 mg as an appetite stimulant. The objectives of this study were to determine the most common adverse effects reported and the dose associated with these signs. Methods Records of cats with mirtazapine exposure (2006-2011) were obtained from the American Society for the Prevention of Cruelty to Animals' Animal Poison Control Center. The following parameters were recorded: signalment, weight, outcome, agent ingested, amount ingested, route of exposure, clinical signs observed, intended of use, onset time of signs and duration of signs. Results The 10 most commonly observed adverse effects reported in 84 cats exposed to mirtazapine included vocalization (56.0% of cats; mean dose 2.56 mg/kg), agitation (31.0%; 2.57 mg/kg), vomiting (26.2%; 2.92 mg/kg), abnormal gait/ataxia (16.7%; 2.87 mg/kg), restlessness (14.3%; 3.55 mg/kg), tremors/trembling (14.3%; 2.43 mg/kg), hypersalivation (13.0%; 2.89 mg/kg), tachypnea (11.9%; 3.28 mg/kg), tachycardia (10.7%; 3.04 mg/kg) and lethargy (10.7%; 2.69 mg/kg). Fifty-nine (70.2%) cases were considered accidental ingestions and 25 (29.8%) cases were given mirtazapine as prescribed. The doses associated with signs of toxicity were 15.00 mg (40 cats), 3.75 mg (25 cats), 7.50 mg (four cats), 30.00 mg (one cat), 18.75 mg (one cat), 11.25 mg (one cat), 5.80 mg (one cat) and 1.88 mg (one cat). For cats with available information, the onset of clinical signs ranged from 15 mins to 3 h, and time to resolution of clinical signs ranged from 12-48 h. Conclusions and relevance The greater number of adverse effects at 3.75 mg rather than 1.88 mg suggests that the latter may be a more appropriate starting dose for stimulating appetite while limiting toxicity. The benefit of dispensing exact doses of mirtazapine is implied given the likelihood of accidental administration of a full tablet (15 mg) and the resulting toxicity.

A double‐blind, placebo‐controlled, randomized study to evaluate the weight gain drug, mirtazapine transdermal ointment, in cats with unintended weight loss

“…In a previous study, treatment with high‐dose (3.75 mg) oral mirtazapine in healthy young cats was associated with an increase in behavior such as vocalization (Quimby, Gustafson, Samber, & Lunn, ). Additionally, a previous retrospective study of orally administered mirtazapine demonstrated significant behavioral adverse effects with accidental administration of an entire 15 mg tablet (Ferguson et al., ). Conversely, the same mirtazapine transdermal ointment as studied here reported no significant change in animal behavior when applied topically to the inner pinna at approximately 5–10X the recommended dose (range 15.8–22.0 mg) to healthy cats for 28 days, (Avenatti, Buhles, Quimby, Labelle, & Poole, ).…”

“…Mirtazapine is classified as a weight gain drug and has been used in cats as an appetite stimulant (Agnew & Korman, ; Ferguson, McLean, Bates, & Quimby, ; Quimby & Lunn, ; Quimby, Summers, Benson, Herndon, & Gustafson, ). In cats with chronic kidney disease, mirtazapine has been shown to promote weight gain and increase food intake in addition to reducing nausea and vomiting (Quimby & Lunn, ).…”

Assessment of compounded transdermal mirtazapine as an appetite stimulant in cats with chronic kidney disease

“…The decision to perform a clinical trial at 3.75 mg was based on preliminary data collected in a previous study in young, normal cats. 11 However, after the conclusion of the current 3.75 mg study, it was noted that some individual cats displayed excessive vocalization, and as these types of behavioral side effects have been demonstrated to be dose related, 7,13 a follow-up study at the 1.88 mg dose was initiated. Data indicate that CTM is effective at the lower 1.88 mg dose, similar to a previous study in oral mirtazapine.…”

ACVIM consensus statement on pancreatitis in cats

“…lethargy) with more adverse effects noted at higher dosages. 151 An additional benefit of mirtazapine may be its antiemetic activity. 152 Mirtazapine transdermal ointment can be used in cats and generally is well-tolerated and efficacious.…”