Veterinary Internal Medicine Nursing

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45 | Help, my patient has eaten rat poison! The vet nurse's guide to anticoagulant rodenticide toxicity

Laura Jones

Anticoagulant rodenticide toxicity is one of the most common toxicities reported in dogs and can cause severe haemorrhage if not identified and managed quickly.

These patients often present as emergencies and can require intensive treatment and nursing care - and how to deliver that care is exactly what we’ll be diving into in this episode.

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So, what is anticoagulant rodenticide toxicity?

Anticoagulant rodenticides come in various formulations, each with different active ingredients. We can divide these into first-generation anticoagulant rodenticides, which tend to be warfarin-based, and second-generation rodenticides, which tend to be coumarin-based.

In general, first-generation rodenticides are less potent, with rodents needing to consume them multiple times to cause death. Second-generation agents, however, are more powerful, requiring a lower dosage to cause toxicity.

How do anticoagulant rodenticides work?

Anticoagulant rodenticides interfere with the activity of vitamin K. They do this by inhibiting an enzyme which is needed to recycle and produce vitamin K1.

Vitamin K1 is necessary to create our vitamin-K-dependent clotting factors, including factors II, VII, IX and X. Factor II - prothrombin - is converted into thrombin, which is converted to fibrin. As fibrin gives our clots strength, stability and durability, bleeding results if this process is inhibited.

So once our patients ingest anticoagulant rodenticide, they lose the ability to create new clotting factors as they lack the vitamin K needed to do so. They have an initial ‘supply’ of clotting factors, lasting between 24-64 hours; after this time, clotting times will increase, and signs of bleeding will be noted.

What signs do we see in these patients?

The clinical signs depend on whether the client has witnessed the patient ingest rodenticide and how recently it was consumed.

In some cases, patients may be entirely clinically normal if they have eaten the toxin recently and still have sufficient clotting factors to prevent bleeding. However, in most cases, patients present with evidence of bleeding.

Signs seen include:

  • Inappetence

  • Lethargy

  • Weakness

  • Epistaxis

  • Haemothorax

  • Pulmonary haemorrhage

  • Respiratory distress

  • Haemoptysis

  • Petechiation

  • Pale MMs

  • Haemoabdomen

  • Haematemesis

  • Melena

  • Haematochezia

  • Haematuria

  • Tachycardia and signs of transfusion-dependence

Bleeding is primarily associated with body cavities, such as the chest, abdomen, and mediastinum, though bleeding into the joints and central nervous system has also been reported.

How do we diagnose these patients?

Diagnosis begins by collecting a thorough clinical history - something we are ideally placed to do as nurses and technicians. 

In many cases, rodenticide ingestion will be witnessed or highly suspected based on whether anticoagulant rodenticides have been used in the home or garden. 

If possible, we need to ascertain which specific rodenticide has been used since many active agents exist, each with particular considerations.

Then, it’s time to think about tests.

The tests performed depend on whether our patient is clinically affected, ie, whether they’re showing signs of bleeding.

In non-clinically affected patients, tests to perform include either a PCV and total solids measurement or a complete haematology alongside clotting times (APTT and PT).

Of our two clotting times, PT will increase first - because the clotting factors affected by anticoagulant rodenticide are on the extrinsic and common coagulation pathways. If the patient’s PT is elevated, even if they are not showing clinical signs, they need to be treated with vitamin K, and PT levels are remeasured 48 hours after finishing treatment.

No treatment is required if the PT is normal and the patient is asymptomatic.

In a clinically affected patient, tests to perform include coagulation times, PCV and total solids at admission, and blood typing +/- cross-matching as needed if a transfusion is required. PCV, total solids and coagulation times are repeated regularly throughout hospitalisation and treatment until they normalise.

Clinically affected patients present with evidence of bleeding - usually into body cavities. Diagnostic imaging, such as abdominal ultrasound, thoracic point-of-care ultrasound or thoracic X-rays are also often required. These may show evidence of pleural, pulmonary, or abdominal haemorrhage.

So that’s diagnosis, but how do we treat these patients?

Let’s start by looking at decontamination.

Patients who ingest anticoagulant rodenticide will require decontamination, even if they’re not symptomatic. If ingestion has occurred within 4 hours of presentation, vomiting should be induced.

Activated charcoal can also be administered. However, this is unlikely to be effective unless administered within 4-8 hours of ingestion.

And then there’s treatment…

Clinically affected patients require rapid treatment and often intensive monitoring and care.

Treatment includes administering vitamin K1 for at least 21 days. Oral administration (with a meal, since vitamin K is a fat-soluble vitamin) is preferred to prevent haematomas from forming at injection sites.

As the effects of vitamin K1 are not immediate, a blood transfusion will be needed in an emergency. Frozen plasma, fresh frozen plasma, and cryo-supernatant all contain our vitamin K-dependent clotting factors, so they can all be used to manage anticoagulant rodenticide toxicity.

In addition, if the patient is markedly anaemic from their bleeding (which, thankfully, is uncommon), they will need either packed red blood cells alongside their plasma or they can be given whole blood. If you don’t have whole blood or packed cells available, an autotransfusion can be performed if the patient is bleeding into their thoracic or abdominal cavity - just remember, though, that this blood does not contain clotting factors, so plasma still needs to be administered alongside this.

Alongside blood products, our patients need supportive treatment, such as gastroprotectants (especially in the event of melena), antiemetics, and oxygen therapy, depending on the location of their bleeding.

And what about nursing care?

Nursing care of the anticoagulant rodenticide toxicity patient is vast and includes careful monitoring of cardiovascular status and monitoring for evidence of further bleeding alongside general nursing care.

Patients with pulmonary or pleural haemorrhage require respiratory support, including oxygen therapy, a hands-off approach and minimal and gentle handling to avoid worsening respiratory distress.

Where our patients have an increased risk of bleeding, we must keep them calm and rested and handle them carefully to prevent further bleeding. This means avoiding jugular venepuncture, only using small peripheral vessels for repeat sampling, and avoiding IM +/- SC injections where possible.

Patients receiving transfusions require careful monitoring to identify transfusion reactions and react quickly if one is noted. We’ll be chatting about transfusions in our next episode, so make sure you listen to that one next!

We tend to keep our clinically-affected patients hospitalised for inpatient treatment until PT is normal. They can then be discharged on ongoing oral vitamin K1 treatment and treated as an asymptomatic patient. 

The patient’s clotting times are rechecked 2-3 days after their last dose of vitamin K1, and treatment is stopped when levels remain normal.

At home, clients should monitor the patient carefully for bleeding and keep them calm and rested until they have completely recovered and their PT is normal.

So that’s an overview of anticoagulant rodenticide toxicity! The treatment and care requirements for these patients can be vast and vary depending on how quickly after ingestion we see the patient and how clinically affected they are. This starts with understanding how anticoagulant rodenticides work and their impact on our patients - exactly what we’ve covered today!

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Thanks for learning with me this week, and I’ll see you next time!

References and Further Reading