Metaldehyde Toxicosis in Dogs and Cats: Diagnosis and Treatment

Bottom line

Metaldehyde toxicosis is an acute, potentially fatal CNS toxidrome requiring immediate control of tremors, seizures, hyperthermia, acid-base derangement, and perfusion while decontamination is pursued when safe. There is no specific antidote.[1] Intravenous lipid emulsion is not established standard therapy; severe refractory canine cases may warrant early consultation with an extracorporeal service, but the clinical dialysis evidence remains limited.

Exposure and pathophysiology

Metaldehyde is the active ingredient in many slug and snail baits. Dogs and cats are the companion species most often affected, and products may be granules, pellets, liquid, powder, meal, gel, or paste.[1] Obtain the package, formulation, active-ingredient concentration, estimated amount missing, time of access, and any vomitus or bait sample without delaying stabilization.

The CNS is the primary target. Merck Veterinary Manual identifies ataxia, seizures, hyperthermia, hypersalivation, and tremors as the predominant clinical signs; vomiting and diarrhea can accompany the neurologic syndrome.[1] Persistent motor activity can drive hyperthermia, rhabdomyolysis, metabolic acidosis, hypoventilation under heavy sedation, and secondary organ injury. Cats can also show dyspnea, muscle spasms, mydriasis, opisthotonos, pronounced nystagmus, and stimulus-evoked seizures.[1]

Recognition and diagnosis

Treat a compatible acute-onset tremor or seizure syndrome with known or plausible molluscicide access as presumptive metaldehyde toxicosis while excluding other immediately actionable causes. Differentials include other tremorgenic or convulsant toxicants, hypoglycemia, hypocalcemia, primary epilepsy, inflammatory brain disease, and head trauma. Blue or green gastric material can support exposure but is neither required nor specific.

Toxicological confirmation can be performed on gastric contents, urine, or serum.[1] Baseline evaluation should prioritize temperature, glucose, venous or arterial blood gas, electrolytes, renal and hepatic values, CK, urinalysis, perfusion, oxygenation, and coagulation testing as dictated by severity. Serial testing is more useful than a single normal panel when tremors, prolonged hyperthermia, or shock have occurred.

The best prospective canine dataset enrolled 26 dogs. Ataxia occurred in 18, convulsions in 17, hypersalivation in 15, and tremors in 15; 21 of 26 survived, an overall survival rate of 81%.[2] These counts describe that cohort rather than diagnostic sensitivities. An earlier retrospective series of 18 dogs found seizures, hyperthermia, tachycardia, and tremors most commonly; metabolic acidosis was common, and survival was 83% (15/18).[3]

Decontamination and initial stabilization

Secure the airway when mentation, seizure activity, or treatment compromises ventilation. Establish IV access, control active motor activity, support perfusion, and measure temperature before attempting GI decontamination. Emesis is inappropriate once neurologic signs, impaired airway protection, or aspiration risk are present.

For a recent ingestion before severe signs, Merck recommends activated charcoal 1–3 g/kg PO once, in combination with a cathartic, ideally within 60 minutes.[1] Multiple activated-charcoal doses are not recommended because evidence for enterohepatic recirculation is lacking.[1] Balance any possible adsorption benefit against aspiration risk; intubation does not make gastric delivery risk-free in a hemodynamically unstable or severely hyperthermic patient.

There is no evidence-based role for home decontamination. Owners en route should be told not to induce vomiting or administer food, oil, milk, charcoal, or salt unless specifically directed by a veterinarian or animal poison-control service.

Tremor, seizure, and temperature control

Rapid suppression of sustained muscle activity is central to treatment. Merck identifies methocarbamol as the drug of choice for tremors at 55–220 mg/kg slow IV to effect, repeated as needed, without exceeding 330 mg/kg in 24 hours.[1] Titrate to motor control while monitoring mentation, airway protection, ventilation, blood pressure, and temperature.

Use anticonvulsants for seizure activity and escalate to general anesthesia with airway control and ventilation when seizures remain refractory. In the 2007 series, general inhalant anesthesia was required in 9 of 18 dogs whose seizures did not respond to anticonvulsants.[3] This is a marker of the intensity sometimes required, not evidence that inhalant anesthesia is superior to another anesthetic strategy.

Apply active cooling while severe hyperthermia persists, alongside control of the muscle activity producing heat. Merck advises stopping cooling once temperature reaches 39.7°C (103.5°F) and monitoring temperature every 1–2 hours thereafter to avoid overshoot hypothermia.[1] Correct metabolic acidosis and electrolyte abnormalities based on measured deficits rather than empiric bicarbonate alone.

Monitoring and delayed injury

Continue cardiorespiratory, neurologic, renal, temperature, acid-base, and urine-output monitoring until motor activity is controlled without escalating medication and the patient maintains ventilation and perfusion. CK elevation, pigmenturia, rising creatinine, hypoglycemia, coagulopathy, or persistent acidosis should change the monitoring and fluid plan.

Delayed hepatic injury is uncommon but documented. Merck recommends evaluating hepatic parameters for 2–3 days after clinical resolution.[1] This is especially relevant after severe hyperthermia, prolonged seizures, hypotension, or an initially abnormal hepatic panel.

Prognosis is generally favorable with rapid, aggressive supportive care. Merck states that patients surviving the first 24 hours have a good prognosis.[1] That statement should not shorten observation in a patient still requiring anticonvulsants, anesthesia, cooling, ventilatory support, or correction of organ dysfunction.

Intravenous lipid emulsion

ILE should not be presented as a specific antidote or routine first-line therapy. Merck notes that metaldehyde is not highly lipophilic and considers ILE unlikely to help.[1] Published successes are case-level evidence confounded by concurrent decontamination, anticonvulsants, fluids, anesthesia, and time.

The 2026 dialysis series is also informative about this limitation: all three dogs had received medical therapy that included gastric decontamination and ILE without improvement in their severe neurologic condition before extracorporeal treatment.[5] This does not establish that ILE worsened outcome; it shows only that it did not produce the needed clinical response in those three cases. If ILE is considered in a refractory patient, document its adjunctive, evidence-limited status and monitor for complications and interference with laboratory or extracorporeal procedures.

Extracorporeal removal

Metaldehyde can be removed from plasma extracorporeally, but the evidence layers must remain separate. A 2016 experiment used metaldehyde-fortified canine plasma and no live animals. Hemodialysis, charcoal hemoperfusion, and combined hemodialysis/hemoperfusion each reduced concentration by more than 95% after the plasma volume was processed 4 times, 8 times, and 2 times, respectively.[4] These are ex vivo circuit results, not clinical survival or dosing data.

Clinical evidence has expanded but is still small. A 2026 case series included three dogs with seizures and uncontrollable tremors after metaldehyde ingestion. Neurologic signs resolved in all three during a single 4-hour session using a medium cut-off hemodialyser, without reported adverse effects. In one dog (Patient 2), calculated dialytic clearance was 12.5 times the measured intrinsic clearance; the authors cautioned that intrinsic clearance may have been underestimated.[5] The uncontrolled design, concurrent care, and tiny sample prevent a universal treatment threshold.

Consider early extracorporeal consultation for severe signs that remain refractory despite appropriate tremor, seizure, temperature, airway, and perfusion management, particularly when prolonged anesthesia or organ injury appears likely. Transfer feasibility, vascular access, hemodynamic stability, toxin timing, local expertise, and the risks of delaying care all matter.

Neurologic outcome

Reactive seizures during the acute toxidrome do not automatically justify indefinite antiseizure medication. In the 2023 prospective study, 9 surviving dogs with convulsions were followed for at least 3 years, and none developed another seizure episode or neurologic sequelae.[2] Apply that result to dogs that recover from an acute toxic event; it does not exclude another epilepsy diagnosis when seizures recur after recovery or when the exposure history is uncertain.

Cat-specific outcome evidence is much thinner. Merck reports that recovery in cats takes approximately 2 weeks without sequelae and notes that secondary liver disease or blindness has not been reported in cats.[1] Avoid importing canine survival percentages, dialysis response, or long-term seizure conclusions into feline prognostication.

Frequently Asked Questions

Is there an antidote for metaldehyde toxicosis? No. Merck Veterinary Manual states that no specific treatment exists; management centers on safe decontamination, stabilization, control of tremors and seizures, correction of hyperthermia and metabolic acidosis, and organ monitoring.[1]

What is the activated-charcoal regimen? For recent ingestion before severe signs, Merck Veterinary Manual recommends activated charcoal 1–3 g/kg PO once, with a cathartic, ideally within 60 minutes.[1] Multiple doses are not recommended because evidence for enterohepatic recirculation is lacking.

What is the methocarbamol dose for metaldehyde tremors? Merck Veterinary Manual recommends 55–220 mg/kg slow IV to effect, repeated as needed, with a maximum of 330 mg/kg in 24 hours.[1] Titrate alongside airway, ventilation, blood-pressure, temperature, and neurologic monitoring.

Is intravenous lipid emulsion standard therapy? No. Merck Veterinary Manual considers metaldehyde insufficiently lipophilic for ILE to be likely helpful.[1] Case reports and small series cannot separate ILE from concurrent supportive care, so it remains an evidence-limited adjunct rather than a specific antidote.

Does laboratory dialysis evidence prove clinical benefit? No. Mauser et al. tested metaldehyde-fortified canine plasma with no live animals; all three extracorporeal methods removed metaldehyde, but those results demonstrate circuit clearance rather than patient benefit.[4]

What does the 2026 hemodialysis series show? Rodary et al. reported three dogs with severe neurologic signs whose signs resolved during a single 4-hour medium cut-off hemodialysis session. In one dog (Patient 2), calculated dialytic clearance was 12.5 times the measured intrinsic clearance; the authors cautioned that intrinsic clearance may have been underestimated.[5] This is promising clinical evidence, but it is an uncontrolled three-case series.

Do recovered dogs need long-term antiseizure medication? Not solely because they had reactive seizures during confirmed acute metaldehyde toxicosis. Dutil and Berny followed 9 surviving dogs with convulsions for at least 3 years, and none had another seizure or neurologic sequela.[2] Recurrent seizures after recovery require a fresh diagnostic assessment.

How long should hepatic parameters be monitored? Merck Veterinary Manual recommends evaluating hepatic parameters for 2–3 days after clinical resolution because delayed liver damage can occur, although it is rare.[1] Extend or intensify monitoring when clinical severity or serial laboratory results warrant it.