Emergency Protocol: What To Do If Your MDR1 Dog Was Given a Dangerous Drug

I wrote this protocol after consulting on a case where the emergency veterinarian had never treated MDR1 toxicity. That dog, a 3-year-old Sheltie named Biscuit who had been given loperamide by her well-meaning owner, survived because the owner had this information ready and could guide the ER team through the initial stabilization. Biscuit spent four days in the ICU and recovered fully. Not all dogs are that lucky.

Immediate Actions (First 30 Minutes)

Step 1: Assess Your Dog

Look for these signs of P-gp substrate toxicity:

• Mild (within 1-4 hours of exposure): Hypersalivation, dilated pupils, mild disorientation
• Moderate: Ataxia (stumbling, uncoordinated movement), tremors, vomiting, apparent blindness
• Severe: Unable to stand, severe tremors or seizures, unresponsive, slow breathing, coma

Step 2: Do NOT Induce Vomiting

If your dog is showing neurological signs, DO NOT induce vomiting. Neurologically impaired dogs can aspirate vomit into their lungs, causing potentially fatal aspiration pneumonia. Let the veterinarian decide on decontamination strategy.

Exception: If your dog received the drug within the last 15-20 minutes AND shows no neurological signs, call your veterinarian or ASPCA Poison Control (888-426-4435) immediately to discuss whether inducing vomiting is appropriate. They may recommend it before signs develop.

Step 3: Call Ahead to the Emergency Clinic

Call the emergency veterinary clinic while you are on your way. Tell them:

1. "My dog has the MDR1 mutation and was given [DRUG NAME]."
2. "The dose was approximately [DOSE] given [TIME] ago."
3. "Current symptoms are [DESCRIBE WHAT YOU SEE]."
4. "I have MDR1 toxicity treatment information I can share with your team."

Information for the Emergency Veterinarian

Print or screenshot this section. Give it to the ER team immediately upon arrival. Not all veterinarians have extensive experience with MDR1 toxicity, and this information can guide their treatment.

Treatment Protocol for Veterinarians

Decontamination (if appropriate):

• Consider activated charcoal (1-2 g/kg PO) if ingestion within 2 hours and patient is neurologically intact
• Gastric lavage may be considered in severe cases with recent ingestion
• Do NOT induce vomiting if neurological signs present

Supportive Care:

• IV fluid support (crystalloids at maintenance to 1.5x maintenance)
• Temperature regulation (hypothermia is common; warm fluids, blankets)
• Seizure control: Diazepam 0.5-1 mg/kg IV PRN; consider levetiracetam for ongoing seizure management
• Respiratory support: Monitor SpO2; supplement oxygen; prepare for intubation if respiratory depression occurs
• Nutritional support via NG tube if prolonged coma expected

For Loperamide Toxicity Specifically:

• Naloxone may provide partial reversal (0.04 mg/kg IV, repeat as needed)
• Monitor for re-sedation as naloxone duration is shorter than loperamide
• Consider naloxone CRI if repeated doses required

Monitoring Parameters:

• Neurological status every 2-4 hours
• Respiratory rate and effort
• Heart rate and rhythm (bradycardia common with opioid toxicity)
• Temperature (hypothermia indicates worsening CNS depression)
• Blood pressure if equipment available

Drug-Specific Timelines

Ivermectin Toxicity

Peak effects typically occur 12-24 hours after ingestion. Dogs may appear normal for several hours before signs develop. Once signs appear, expect 48-72 hours to peak severity, then gradual improvement over 7-14 days. Some dogs have residual neurological effects for weeks.

Fatal ivermectin toxicity typically involves respiratory depression progressing to respiratory arrest. Dogs that survive the first 72 hours with adequate respiratory support usually recover.

Loperamide Toxicity

Onset is faster than ivermectin, typically 1-4 hours. Peak effects at 4-8 hours. Duration varies with dose but typically 24-48 hours in M/M dogs. Respiratory depression is the primary life-threatening concern.

Naloxone can be dramatically effective for loperamide toxicity but must be re-dosed because its duration of action (30-90 minutes) is shorter than loperamide's effects in MDR1 dogs.

Acepromazine Overdose/Sensitivity

Acepromazine at normal doses in M/M dogs causes prolonged (8-24 hour) sedation rather than acute toxicity. Hypotension is the primary concern. Treat with IV fluids and repositioning. Most dogs recover without specific intervention but require monitoring.

Prognosis

Prognosis depends on the drug, dose, and how quickly treatment begins:

• Loperamide, single dose, treatment within 2 hours: Generally good with supportive care
• Loperamide, repeated doses: Guarded to poor
• Ivermectin, moderate dose (200-400 mcg/kg): Fair with aggressive supportive care
• Ivermectin, high dose (>600 mcg/kg): Guarded; survival depends on ICU capability
• Acepromazine overdose: Generally good; most dogs recover with monitoring

The most important prognostic factor is early recognition and treatment. Dogs that receive prompt supportive care have significantly better outcomes than those where treatment is delayed.

Recovery and Aftercare

Dogs recovering from MDR1 drug toxicity may have:

• Residual ataxia for days to weeks
• Apparent visual deficits (usually temporary)
• Appetite changes
• Behavioral changes (anxiety, disorientation)

Most dogs make full recoveries, but some have lasting neurological effects, particularly if hypoxia occurred during the acute phase. Follow up with your regular veterinarian 2 weeks after discharge, and sooner if you notice any concerning signs.

Prevention Is Everything

This emergency should never happen. If you are reading this because your dog was just poisoned, I am sorry, and I hope the information helps. But for everyone else: TEST YOUR DOG.

After any emergency, return to our Drug Avoidance List and review it with every family member and caregiver who might give your dog medication. Post it on your refrigerator. Add it to your dog's file at every veterinary clinic you might use.

Make sure your dog's MDR1 status is permanently documented in veterinary records. Consider a medical alert collar tag. These simple steps prevent emergencies from happening in the first place.

For owners who have not yet tested their herding breed dogs, our Testing Options guide explains the simple, affordable process. For breeders working to reduce MDR1 incidence in their lines, our Breeding Decisions guide offers evidence-based strategies.

For comprehensive background on the molecular genetics of MDR1 and why P-glycoprotein deficiency creates these dangerous drug sensitivities, start with our foundational guide.