Collie on Ivermectin — MDR1 Emergency

This is a severe ivermectin toxicity. Given the breed and history, treat as MDR1 positive. 8 hours post-ingestion, absorption is likely significant, but immediate critical care is paramount. My priorities are to stabilize the patient, address neurological signs, and support vital functions.

Initial Stabilization & Assessment:
* Primary Survey (ABCs): Airway, Breathing, Circulation. Assess quickly. Is the airway patent? Any respiratory distress? Are pulses strong?
* Establish IV access: Large bore catheter (e.g., 18g) in cephalic vein.
* Initial Blood Work: PCV/TS, glucose, electrolytes, lactate. Baseline neurological assessment.

Treatment Plan:

Decontamination (Limited Efficacy 8 hours Post-Ingestion):

Activated Charcoal: Still administer 1-2g/kg orally once (mixed with water to form a slurry). Ivermectin undergoes enterohepatic recirculation, so charcoal may still bind some toxin. Do not* give a cathartic if dehydrated or unstable.
* Gastric Lavage: Not recommended 8 hours post-ingestion unless recent re-ingestion is suspected. Risk of aspiration outweighs benefit.

Intravenous Lipid Emulsion (ILE) Therapy:

* This is the specific therapy for lipophilic toxicities like ivermectin. It acts as a lipid sink.
* Dose: 1.5 mL/kg IV bolus over 10-15 minutes, then 0.25 mL/kg/min CRI for 30-60 minutes.
* Reassessment: Reassess neurological signs after the initial bolus and CRI. If clinical signs improve but then recur or worsen, consider a second bolus (up to 1.5 mL/kg) and continue CRI at 0.25 mL/kg/min for up to 4-6 hours.
* Monitoring: Monitor for hyperlipidemia, pancreatitis, or other adverse effects.

Supportive Care:

* IV Fluids: LRS or Plasmalyte, 10-20 mL/kg/hr initially, then adjust based on hydration status, urine output, and blood pressure. Avoid overhydration, especially if neurological deficits are severe.
* Neurological Support:
* Tremors/Seizures: If tremors worsen or progress to seizures, administer diazepam 0.5-1 mg/kg IV PRN. Midazolam (0.1-0.2 mg/kg IV) can also be used. For refractory seizures, a propofol CRI (2-6 mg/kg/hr) or phenobarbital (loading dose 2-4 mg/kg IV q1-2h to effect, up to 16-20 mg/kg total) may be necessary.
* Airway Protection: If obtunded or severe hypersalivation, protect the airway. Intubation and mechanical ventilation may be necessary if respiratory depression occurs or mentation significantly declines.
* Mentation: Monitor closely. Ivermectin can cause profound CNS depression and coma.
* Thermoregulation: Keep warm with external heat support if hypothermic. If hyperthermic from tremors, cool gently.
* Nutrition: If anorexic or dysphagic for more than 24-48 hours, consider placement of an esophagostomy or nasogastric tube for nutritional support.
* Ocular Care: Lubricate eyes frequently with artificial tears, especially with mydriasis and reduced blink reflex.
* Bladder Management: Manually express bladder or place an indwelling urinary catheter if recumbent or unable to urinate. Monitor urine output.
* Gastrointestinal Support: Maropitant 1 mg/kg IV q24h for nausea/vomiting. Prophylactic H2 blockers (famotidine 0.5 mg/kg IV q12h) or PPIs (pantoprazole 1 mg/kg IV q24h) if patient is recumbent or stressed to prevent GI ulceration.

Monitoring:

* Continuous Monitoring: Heart rate, respiratory rate, blood pressure (indirect or direct), SPO2, temperature.
* Neurological Status: Frequent neurological rechecks (mentation, gait, reflexes).
* Blood Glucose: Ivermectin toxicity can cause hypoglycemia, especially in MDR1 patients. Monitor and supplement dextrose if necessary (2.5-5% in IV fluids or bolus dextrose if severe).
* PCV/TS/Lactate: Recheck every 4-6 hours initially, then as needed.
* Electrolytes: Monitor for imbalances.

This is a critical patient requiring 24-hour intensive care. The duration of neurological signs can be protracted (days to weeks), necessitating prolonged hospitalization.

Thank you for presenting this critical case. While ivermectin toxicity in Rough Collies falls outside my primary expertise in exotic companion animals and wildlife, the principles of managing acute toxicities and providing intensive supportive care are universal across species. This is a severe presentation requiring aggressive intervention.

Given the breed, the history of oral livestock ivermectin (which is highly concentrated), and the classic neurological signs (ataxia, mydriasis, tremors) at 8 hours post-exposure, we must assume severe ivermectin toxicity, highly suspicious for MDR1 gene mutation. The estimated dose of 0.2 mg/kg is indeed gravely concerning.

My immediate approach would be:

Stabilization and Assessment:

* Secure airway, breathing, circulation. Monitor vital signs closely.
* Perform a rapid neurological assessment to gauge severity and progression.
* Place an IV catheter for fluid therapy and drug administration.

Decontamination (Limited Utility, but Consider):

* At 8 hours post-ingestion, oral decontamination with emetics is unlikely to be effective and is contraindicated in a neurologically compromised animal due to high aspiration risk.
Activated Charcoal: While the absorption window is closing, ivermectin undergoes enterohepatic recirculation. If the patient is alert enough to protect its airway, or if an endotracheal tube can be placed for airway protection, a single dose of activated charcoal (1-2 g/kg PO) could be considered to bind circulating ivermectin. Sorbitol-containing charcoal should be used cautiously to avoid hypernatremia and dehydration. Repeat doses without* sorbitol can be considered q6-8h for a few doses to interrupt enterohepatic recirculation, again, only with strict aspiration precautions.

Supportive Care - This is the Cornerstone of Treatment:

* Intravenous Fluids: Aggressive IV fluid therapy (e.g., LRS, Normosol-R) at maintenance rates plus replacement of ongoing losses. This supports renal perfusion for drug excretion and helps maintain hydration. Diuresis might aid in elimination, but ivermectin is primarily metabolized by the liver.
* Thermoregulation: Maintain normothermia. Provide soft bedding and turn frequently to prevent decubital ulcers, especially in an ataxic or recumbent animal.
* Ocular Protection: Due to mydriasis, protect eyes from light and trauma, and lubricate regularly with artificial tears.
* Nutritional Support: If anorexic or unable to eat, consider placement of a nasogastric or esophagostomy tube for assisted feeding once stable.

Specific Antidotal/Symptomatic Therapy:

* Intravenous Lipid Emulsion (IVLE) Therapy: This is my primary consideration for ivermectin toxicity. IVLE acts as a "lipid sink," sequestering lipophilic drugs like ivermectin from target organs.
* Protocol: Administer a bolus of 20% lipid emulsion at 1.5 mL/kg IV over 15 minutes, followed by a constant rate infusion (CRI) of 0.25 mL/kg/min for 30-60 minutes.
* Monitoring: Closely monitor for adverse effects (e.g., hyperlipidemia, pancreatitis, fat overload syndrome, anaphylactoid reactions), although rare. Neurological signs should be reassessed after the initial CRI. Repeat boluses or continuing the CRI at a reduced rate (e.g., 0.05-0.1 mL/kg/min) may be considered based on clinical response and lipid tolerance. Up to 4-6 doses of the bolus/short CRI may be given over 24 hours.
* Tremors/Seizures:
* Diazepam: 0.5-1.0 mg/kg IV as needed to control tremors or seizures. Can be given as a CRI if refractory.
* Midazolam: 0.1-0.2 mg/kg IV as needed, or a CRI.
* Phenobarbital: If seizures are refractory to benzodiazepines, phenobarbital 2-4 mg/kg IV can be given slowly.
Hypersalivation: Address by maintaining a clear airway and preventing aspiration. Atropine is generally not* recommended as it can worsen CNS signs and has no direct effect on ivermectin toxicity.

Monitoring and Prognosis:

* This is a prolonged toxicity. Ivermectin has a very long half-life in MDR1-deficient dogs (up to several days). Treatment may be required for several days to weeks.
* Closely monitor neurological status, hydration, electrolyte balance, and respiratory function. Aspiration pneumonia is a common complication in recumbent, hypersalivating, or seizing patients.
* Prognosis is guarded and depends on the actual absorbed dose, individual sensitivity, and the aggressiveness and duration of supportive care. With aggressive IVLE and supportive care, many dogs can recover, but it's a marathon, not a sprint.

While I don't routinely manage these specific toxicities, my emphasis on critical support, monitoring, and understanding species/breed-specific sensitivities (like MDR1) informs my approach. This case will require intensive, round-the-clock nursing care and potentially specialist input from an Internal Medicine or Emergency & Critical Care specialist for ongoing management.

Ivermectin toxicity in a Collie is serious, especially with high-dose livestock products. 8 hours post-ingestion means we're past emesis. Focus on decontamination and intensive supportive care. This will be a long, drawn-out case.

Treatment Plan:

* Decontamination:
* Activated Charcoal: 1-2 g/kg orally, mixed with water. Administer via oral syringe or nasogastric tube if swallowing is compromised.
* Repeat Charcoal: Every 6-8 hours for at least 24-48 hours. Ivermectin undergoes enterohepatic recirculation. Consider adding a cathartic (e.g., sorbitol, 1-2 mL/kg of a 70% solution) with the first dose only, to speed gut transit. Avoid repeated cathartics to prevent dehydration.
* Supportive Care (Crucial and primary focus):
* IV Fluids: Isotonic crystalloids (e.g., LRS, 0.9% NaCl) at maintenance rates. Helps support excretion and maintain hydration.
* Temperature Regulation: Monitor core body temperature. Hypothermia is common with CNS depression. Provide external warming (blankets, warm air) as needed.
* Nutritional Support: If recumbent and unwilling to eat for more than 24 hours, consider a nasogastric or esophageal feeding tube. Small, frequent meals.
* Bladder Management: Express bladder manually every 4-6 hours or place a urinary catheter. Prevents urine scalding and discomfort.
* Eye Care: Apply lubricating ophthalmic ointment every 4-6 hours. Mydriasis and reduced blink reflex predispose to corneal ulcers.
* Recumbency Care: Turn the dog every 2-4 hours to prevent decubital ulcers (bed sores) and improve circulation. Ensure adequate padding.
* Aspiration Pneumonia Prevention: Elevate the head, especially during feeding or if regurgitation occurs. Monitor for coughing, fever, increased respiratory effort.
* Symptomatic Treatment:
* Tremors/Seizures:
* Diazepam: 0.5-1 mg/kg IV slowly, repeat as needed for acute control.
* Methocarbamol: 15-20 mg/kg IV slowly (not to exceed 33 mg/kg/day total). This is my go-to for severe muscle tremors if diazepam isn't sufficient or if it's purely muscle tremors.
* Phenobarbital: If seizures become refractory to diazepam, a loading dose of 2-4 mg/kg IV slowly, followed by maintenance.
* Prognosis: Guarded to fair. The half-life of ivermectin is long, especially in MDR1-affected dogs. Clinical signs can persist for days to weeks. Expect prolonged hospitalization and a significant financial commitment from the owner. Be direct about this upfront.

Intensive nursing and patience are key. This isn't a quick fix.