Rat Bait Toxicosis in a Dog

Sara, a 4-year-old spayed pit bull mix, presented to the emergency clinic after ingesting an unknown type of rodenticide. 

Clinical PresentationDuring a visit with another family, Sara accidentally ingested what her owner believed to be approximately one-half cup of green-colored mouse and rat poison. The owner stopped at home before bringing Sara to the clinic, resulting in a 30-minute delay.

HistoryThree months before presentation, Sara underwent a physical examination and received scheduled vaccinations. At the time, she was in excellent health and weighed 55 lb.

TreatmentBecause ingestion was recent, emesis was induced with 20 mL of hydrogen peroxide to allow appropriate decontamination. Five minutes later, Sara vomited 1 cup of green pellets. Delayed decontamination (hours out) may be ineffective if toxin has moved out of the stomach.

Related Article: Ingestion of an Unknown Rodenticide in a Dog

What is your next step?A.    Send the patient home, as there are no further concerns after she vomited the bait.B.    Send the patient home with 7 days of vitamin K1.   C.    Monitor renal panels daily for 2 to 4 days, check electrolytes and baseline prothrombin time (PT) in case of previous unknown exposure, then start vitamin K1 for 30 days.D.    Monitor renal panels (as in answer C) but check the PT at 48 and 72 hours’ post-exposure without vitamin K1.

Correct Answers:C. Monitor renal panels daily for 2 to 4 days, check electrolytes and baseline prothrombin time (PT) in case of previous unknown exposure, then start vitamin K1 for 30 days.orD. Monitor renal panels (as in answer C) but check the PT at 48 and 72 hours’ postexposure without vitamin K1.

Related Article: Evaluating the Bleeding Patient: Point-of-Care Tests

Even though anticoagulants are the most common rodenticides (see Rodenticides), it is not possible to differentiate the 4 to 5 different active ingredients based on color alone (eg, green vs blue). Follow-up blood work is required to ensure that other active ingredients were not ingested.

Rodenticides

• Anticoagulants—Most common type of rodenticide; includes warfarin, bromadiolone, chlorophacinone, difethialone, and brodifacoum

• Neurotoxins—Bromethalin; causes cerebral edema and seizures

• Cholecalciferol—Causes hypercalcemia and soft tissue calcification, including heart, intestines, and (most notably) kidneys

• Zinc phosphide—Releases phosphine gas and may cause damage to tissues with high oxygen demand; signs can include anorexia, vomiting (often with blood), rapid and deep respirations, ataxia, weakness, and seizures; odor of spoiled fish or garlic is suggestive of phosphide rodenticide, and caution must be taken to prevent secondary exposure to pet owners and veterinary professionals (public health risks)

• Aldicarb—Highly toxic carbamate that causes acute onset of drooling, tremors, urination, defecation, and vomiting and can result in death

• Strychnine—Still available and typically causes vomiting, drooling, tremors, disorientation, ataxia, weakness, rigidity, tachypnea or dyspnea, and violent and tetanic seizures

Baseline blood work is imperative (Table 1). Monitoring renal function q24–48h after ingestion can help determine whether cholecalciferol rodenticide is involved. Any evidence of elevated calcium, phosphorus, or renal values warrants immediate, aggressive IV fluid therapy and treatment.

Table 1. Baseline Blood Work

BUN = blood urea nitrogen

If a long-acting anticoagulant is ingested, therapy should include either monitoring the PT for 48 hours after decontamination with no vitamin K1 therapy until the PT results are obtained or prophylactic vitamin K1 therapy at 3 to 5 mg/kg PO q12h for 30 days, followed by checking PT for 48 and 72 hours after the last dose of vitamin K1.

Of note, the risk for rodenticide toxicity can be reduced with decontamination via emesis and activated charcoal if appropriate (eg, toxic dose ingested within the time frame for appropriate emesis induction, asymptomatic patient).

In addition, knowing the color and shape of the bait does not help identify the specific rodenticide involved. When the type of rodenticide is unknown, treatment needs to be aimed at the 4 main types—anticoagulants, neurotoxins, cholecalciferol, and zinc phosphide—because signs of toxicity may not be seen for 1 to 3 days.

Aldicarb, strychnine, and zinc phosphide act quickly, so exposed animals will be symptomatic within minutes to a few hours; however, these rodenticides are rarer.

Related Article: Rodenticide Toxicity

Follow-UpIn this case, the rodenticide was confirmed as bromethalin, and Sara was observed overnight (ie, for 12 hours) to ensure that no neurologic signs developed. In addition, she received a second dose of activated charcoal at 2 g/kg PO 6 hours after presentation and was treated with SC fluids and an antiemetic. Of note, Sara’s baseline PT, electrolytes, and renal panel were normal on day 1 of exposure. Because a long-acting anticoagulant was not involved, vitamin K1 therapy and additional blood work were unnecessary. The patient was released, as decontamination had been successful.

The ASPCA Animal Poison Control Center recommendations for treating bromethalin ingestion are provided in Table 2.

* As recommended by the ASPCA Animal Poison Control Center† 1 oz of 0.01% bromethalin bait contains 2.84 mg of bromethalin

Take Home Messages:

• Not all rodenticides are anticoagulants.

• Until the active ingredient can be appropriately identified, practitioners need to consider all types of rodenticides. Do not assume it is a long-acting anticoagulant.

• Sources of information on bait type:

• EPA registration number

• Pest control official (often will answer message left after business hours)

• Receipt from pest control

HELEN MYERS, DVM, is a consulting veterinarian in clinical toxicology at the ASPCA Animal Poison Control Center in Urbana, Illinois. Before her affiliation with the ASPCA, she worked in private practice and emergency clinics. Dr. Myers earned her DVM from Colorado State University.

JUST ANOTHER RAT BAIT? • Helen MyersReference

1. Bromethalin: The other rodenticide. Dunayer E.Vet Med 98:732-736, 2003.

Suggested Reading

Anticoagulant rodenticides: Deadly for pests, dangerous for pets. Merola V. Vet Med 97:716-722, 2002.Bromethalin. Adams C, Hovda LR. In Osweiler GD, Hovda LR, Brutlag AG, Lee JA (eds): Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Small Animal Toxicology—Ames, IA: Wiley-Blackwell, 2011, pp 769-774.Cholecalciferol poisoning. Morrow C. Vet Med 96:905- 911, 2001.Cholecalciferols. Adams C. In Osweiler GD, Hovda LR,Brutlag AG, Lee JA (eds): Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Small Animal Toxicology— Ames, IA: Wiley-Blackwell, 2011, pp 775-780.Phosphides. Gray S. In Osweiler GD, Hovda LR, Brutlag AG, Lee JA (eds): Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Small Animal Toxicology— Ames, IA: Wiley-Blackwell, 2011, pp 781-790.Rodenticides. Dunayer E. In Poppenga RH, Gwaltney-Brant SM (eds): Small Animal Toxicology Essentials— Ames, IA: John Wiley & Sons, 2011, pp 117-125.