Methylphenidate hydrochloride, a CNS stimulant and piperidine derivative similar in structure and mode of action to amphetamines, is thought to act primarily by blocking presynaptic dopamine transporters.1–7 It is primarily used to treat ADHD in children and human adults2,8 and is the medication most commonly prescribed for that purpose.2,4–6 The prevalence of ADHD has been estimated to range from 3% to 8% in children and as high as 4% to 5% in adults.2,5,8 Misuse and diversion of MPH is well documented and is of particular concern in regard to teenage and college student populations.5,6 The drug is uncommonly used to treat narcolepsy and hyperactivity in dogs.9 Methylphenidate has a wide margin of safety (ie, range between the minimal therapeutic dose and minimal toxic dose) in humans, and most signs of toxicosis result from sympathomimetic stimulation, primarily involving CNS and cardiovascular abnormalities.5,6
The widespread use of MPH among humans puts companion animals at risk of accidental ingestion. Results of a literature search revealed no studies that described the effects of accidental MPH poisoning in multiple dogs. To our knowledge, studies1,10 of the effects of MPH in dogs have been conducted under experimental laboratory conditions and the effects of ER formulations of the drug have not been reported for this species. When the drug was administered experimentally, healthy Beagles survived MPH dosage regimens of > 20 mg/kg/d (> 9.1 mg/lb/d) for 90 days10 and 15 mg/kg/d (6.8 mg/lb/d) for 91 days.1 Death was reported following a dose of 3.1 mg/kg (1.41 mg/lb) in 1 dog, but details of that exposure were not reported.9 Methyphenidate toxicosis was also reported11 following inadvertent administration in a cat. The LD50 for MPH in dogs has not been established.
The purpose of the study reported here was to characterize clinical signs and outcomes of toxicosis associated with ingestion of MPH pills (ie, tablets and capsules) in dogs and to determine effects of the amount (ie, dose) and formulation (IR vs ER) of MPH ingested on the onset, duration, and severity of clinical signs. We sought to determine the minimum dose of MPH that resulted in clinical signs in the dogs of this study and to describe different approaches to management of MPH intoxication in dogs.
Attention-deficit hyperactivity disorder
Animal Poison Control Center
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