Introduction

Toxicosis refers to a disease or pathology caused by a poison or toxin. Toxicosis in veterinary emergency practice is a relatively common occurrence. Toxins can be found in and around the house, and common poisonings in small animal medicine include chocolate, grapes, raisins, house plants and human medications. Poisonous substances may also be found out of the house, in the garden or whilst out on a walk. Common toxins include inappropriate foodstuffs (mycotoxins), slug pellets (metaldehyde) and rat bate/poison (anticoagulants).

These are, of course, only a few of the toxicities seen in practice. The list is extensive and varied; this lecture will review only a few of the common toxins and the disease processes that ensue. Routes of administration are discussed, along with the current treatment recommendations for toxicosis.

Triage and History—The Initial Contact

The telephone is often the first point of contact, and the veterinary nurse taking the call should be well trained and aware of which specific questions to ask.

Example questions include (but are not limited to):

• What has the animal ingested/been exposed to?
• What is the active ingredient on the packet?
• How much? (roughly)
• How long ago?
• Is the animal showing any clinical signs?

The owner may be stressed and unable to answer definitively, asking questions that are succinct, but with compassion may help guide the owner in releasing important information. The owner will often not know exactly how much has been eaten or even what has been consumed if their dog was exercising off-lead, an informed guess may still be useful in these situations if the owner can bring some of the ingested item or the packaging into the practice, that may be helpful. It may be possible to begin some therapy at home already; for example, ocular flushing, although this will depend on patient compliance.

Routes of Administration

There are three main routes of administration of toxins: ocular, dermal and gastrointestinal. Dermal toxicities may make their way onto the patient by solutions falling on the animal at home or application from ill-informed owners; for example, an incorrect dose of a spot on flea treatment or by close contact with an owner who is using medicated lotions or ointments. Gastrointestinal toxicities are relatively common in veterinary practice and occur when the patient ingests the poison per os.

Dosages

When a medication or food item becomes a poison usually depends on the amount consumed, although this is not always the case. For example, grapes and raisins have an idiosyncratic effect on dogs, and the toxic dose has wide variability.¹ Nevertheless, it is important to find out, if possible, how much the patient has ingested; depending on this, the patient may be able to stay at home under close supervision if deemed safe by the veterinary clinician, or need to attend the practice for decontamination and monitoring.

Decontamination

Decontamination depends on the route of the toxin.

For ocular routes, it is recommended to flush the affected eye for a minimum of 15 minutes. The eye should be flushed with 0.9% saline, but tap water is also suitable and can be used if the owner was to attempt this at home—the owner should be advised to flush the eye at home before travelling to the veterinary hospital, if possible.¹ Depending on how cooperative the animal is, a small sedation may be necessary to keep the patient calm and allow for thorough eye irrigation. Where possible, the nose should be kept in a downwards position to prevent contamination of the non-affected eye, commercial contact lens solutions should be avoided.²

Dermal decontamination involves bathing the patient in mild soapy water to remove the toxin as soon as possible; clipping of hair may be indicated in longhaired dogs and cats. Gloves should be worn to protect the caregiver, and care should be taken with small dogs and cats to avoid hypothermia.

Through the gastrointestinal route, decontamination may be more invasive. The decontamination method depends on the amount of time passed between the toxin's ingestion and the patient's demeanour on presentation. If a short amount of time has passed between ingestion and presentation and the patient is not showing neurological signs, vomiting can be induced either with apomorphine for dogs and xylazine or dexmedetomidine for cats.³ Typically, if more than 4 hours have passed between ingestion and presentation, inducing emesis is of little value.¹ Nowadays, it is often advised to visit the hospital to induce vomiting rather than attempting this at home due to potential risks associated with using inappropriate solutions to induce vomiting. All of the medications mentioned above to induce vomiting can cause drowsiness; for this reason, a trained staff member must stay with the patient after administration, which may help limit the risk of aspiration pneumonia. After the stomach contents are expelled, the patient should receive an antiemetic, and cats should also receive a dose of yohimbine or atipamezole as a reversal agent.

If the patient arrives needing decontamination but is already showing neurological signs such as lethargy, obtundation, tremors or seizures, gastric lavage may be the safest course of action. The patient will need to be anaesthetised and intubated for this procedure, and the risks involve aspiration pneumonia along with the risks of undergoing general anaesthesia.

The induction of emesis is contraindicated when the ingestion of corrosive substances or sharp objects is confirmed or suspected.

Specific Treatments for Toxicosis

Antidotes are limited in the poisoned veterinary patient, and due to cost, unknown toxin or unavailability of the antidote, may not be an option. Thankfully, patients often respond well to symptomatic treatment. That being said, a few specific therapies are available.

Activated Charcoal (AC)

Activated charcoal comes in a powder form or ready formulated liquid solution and is given per os. It is often well tolerated when mixed with food. AC is widely prescribed in acutely poisoned patients and is administered to reduce the adsorption of several toxins. AC should be administered as quickly as possible to be of maximum use, ideally within 5 minutes of ingestion of the poison.² However, the reality of veterinary medicine makes this near impossible, with travel time, triage and examination typically taking over an hour.

Multiple doses are recommended to treat toxins that undergo enterohepatic circulation and should be repeated every 4–8 hours for 24 hours (without a cathartic).² However, more recent studies have questioned whether a single dose acts as efficiently as multi-doses.⁴

Intralipid Emulsions (ILE)

ILE is a liquid solution that is administered intravenously (IV). The exact mechanism of action (MOA) of ILE is unknown, but there are several existing theories of how ILE acts. The most supported theories are that it improves cardiac performance and provides a 'lipid sink', in effect sequestering the toxin particles and compartmentalising the drug in the lipid phase resulting in a lower level of the toxin to reach its site of action.

As there are limited studies on the use of ILE in the veterinary field, it should be used with caution and considered for use in patients with local anaesthesia toxicity or toxicity caused by lipophilic drugs, after the patient exhibits significant clinical signs.⁵

Common Toxins

Chocolate

Chocolate is a common household item that can makes its way into our canine patients. The active ingredients in chocolate that causes concern is theobromine, which is a methylxanthine alkaloid, which increases depending on the percentage of cocoa. Methylxanthines inhibit a particular enzyme which has further knock-on effects causing interference with signalling pathways whilst also inhibiting the receptor-mediated actions of adenosine, resulting in stimulation of the cerebral cortex, increased myocardial contraction and an increase in diuresis.¹

Several 'chocolate calculators' are available online to help the veterinary nurse advise the client over the phone. Calculating the amount ingested of cocoa may make a difference in whether the patient can be monitored at home or if they need to be seen and receive treatment.

Treatment for theobromine toxicity may include induction of emesis, administration of multiple doses of AC (due to the enterohepatic recirculation of methylxanthines⁶), fluid therapy and ECG monitoring, along with further symptomatic treatment. Due to the reabsorption of methylxanthines through the bladder epithelium, the patient may be put on a higher fluid rate to increase diuresis, frequent 'bathroom' trips will allow for patients to eliminate urine regularly. The vet may choose to monitor the patient with continuous an ECG in cases where tachycardia and arrhythmias are present. The patient may arrive with restlessness, vomiting, diarrhoea, tachycardia and neurological signs such as tremors or seizure activity.

Rodenticide Poison

Anticoagulant rodenticides (ACR) are again a poison more commonly ingested by dogs than cats, toxicosis following ingesting poisoned mice is possible but thankfully, relatively uncommon.¹ ACRs act by blocking vitamin K from converting to its active form. Vitamin K is essential for the activation of factor II, VII, IX and X, the vitamin-K-dependent factors. When these factors fail to activate, coagulopathies can result, potentially causing intracavity bleeding. The patients' existing vitamin K stores are usually only depleted only after 36–48 hours, meaning that signs of coagulopathy can occur after this time; patients typically present 3–5 days post-ingestion.

Treatment depends on clinical signs. If the owner has witnessed ingestion, induction of emesis is warranted potentially followed by a prescription of vitamin K per os. Further blood tests involving coagulation profiles may be necessary before terminating treatment. If the patient arrives with clinical signs of active bleeding, therapy may involve administering blood products such as fresh frozen plasma (to deliver coagulation proteins) and fresh whole blood or packed red blood cells. Supportive therapy may include thoracentesis and oxygen therapy. Coagulation profiles and haematology blood samples will help guide the treatment plans. Simultaneous treatment with vitamin K can be administered subcutaneously or per os if the patient is well enough to take medication by mouth; per os is the preferred route, as it is absorbed quickly in the GI tract.

Slug Pellets (Metaldehyde)

Slug pellets to deter slugs from crops may also be quite palatable to our four-legged friends and so, unfortunately, find their way into our patients. Metaldehyde is the active ingredient in most slug pellets; metaldehyde itself affects the level of several neurotransmitters, which can lead to neurological symptoms.¹ The onset of action can occur after 30 minutes;¹ meaning, patients may arrive already symptomatic with agitation, ataxia, tremors and twitches or status epilepticus. There is no antidote for these patients, and therapy is supportive.

Treatment includes swift gastric emptying via emesis if the patient is not yet showing neurological signs and via gastric lavage, if neurological symptoms are already present. A single dose of AC may be advantageous but, due to lack of evidence of enterohepatic recycling of metaldehyde, further doses are not currently recommended.¹

Patients may need continued treatment consisting of antiepileptic drugs, muscle relaxants and potentially sedatives or total intravenous anaesthesia (TIVA), along with high-intensity nursing with close vital parameter monitoring and active cooling, if hyperthermia is present.

Hemodialysis may also be indicated in patients with metaldehyde poisoning, where this is available.⁷

Raisins/Grapes

Raisins, grapes, sultanas and currents are all potentially toxic to dogs (currently only anecdotal data regarding poisoning in cats). The mechanism of action is currently unknown, but it is thought that a nephrotoxic agent is involved or an idiosyncratic reaction occurs, leading to hypovolemic shock and renal ischemia.¹ Patients may arrive clinical with diarrhoea, anorexia and lethargy, and symptoms may worsen into acute kidney injury. There is no specific toxic dose as this appears to be variable from case to case, with dried fruit appearing to be more likely to cause adverse reactions.

Treatment consists of decontamination and aggressive fluid therapy, whilst closely monitoring urine output and renal values. Hemodialysis may be necessary for acutely sick anuric patients.

Paracetamol

Paracetamol, also known as acetaminophen, is a common over-the-counter household drug. Veterinary patients may be administered this from misinformed owners or through accidental ingestion, especially liquid formulations with added sweeteners. Paracetamol is far more toxic to cats than dogs; the toxic dose for cats is only 10 mg/kg, whereas for dogs the toxic dose is 100–150 mg/kg.³ Paracetamol toxicity includes signs of methemoglobinemia and hepatic failure/dysfunction. These can lead to a varied presentation of acute and non-acute clinical signs, including tachypnoea, dyspnoea, brown/murky mucus membranes and fatigue, icterus, vomiting and hepatic encephalopathy, with increased liver values on blood work.

Treatment commonly includes decontamination, followed by symptomatic therapy including intravenous (IV) fluids, oxygen, antiemetics, AC and the use of N-acetylcysteine (NAC) as a hepatoprotectant. NAC acts by reducing the production of a toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI) which accumulates during paracetamol toxicity.¹ It is the accumulation of NAPQI that causes oxidative injury, methemoglobinemia and liver injury. Blood transfusions may be necessary for the methemoglobinemia patient to increase oxygen-carrying capacity.

The Role of the Veterinary Nurse

The role of the vet nurse (VN) is integral for the poisoned patient. The VN can be and should be involved with the case throughout their journey from the initial telephone triage to intensive care nursing. Vet nurse responsibilities have a wide range, including triaging, IV catheter placement, administration of drugs and fluid therapy, care and support for the vomiting patient, and patient poisoning for the prevention of aspiration pneumonia. The VN may prepare and monitor general anaesthesia for gastric lavage or may perform the lavage with the veterinary surgeon's supervision. Recovery of patients with a high risk of aspiration pneumonia is highly demanding, and a well-trained VN is a considerable benefit.

The veterinary nurse can help assist the vet in prompt treatment and monitoring of the neurological patient, whilst simultaneously taking the initiative to actively cool and calm the patient with eye and ear coverings, giving the animal a much needed quiet space—even in a busy ER or ICU. The VN may then continue to monitor the intensively ill patient under anaesthesia or sedation, attending to needs such as; turning, eye care, mouth hygiene, urinary care (including urinary catheter placement when necessary) and keeping the veterinary surgeon informed on the latest parameters and if any changes have recently occurred.

Toxicosis patients vary from the puppy who has ingested a small amount of chocolate and may only need home monitoring to the acute kidney injury patient needing hemodialysis. The severely intoxicated patient may require intensive nursing care and can be incredibly rewarding cases for the veterinary nurse.

References

1.  Peterson ME, Talcott PA. Small Animal Toxicology - E-Book. Elsevier Health Sciences; 2013.

2.  Silverstein D, Hopper K. Small Animal Critical Care Medicine - E-Book. Elsevier Health Sciences; 2014.

3.  King LG, Boag A. BSAVA manual of canine and feline emergency and critical care. BSAVA; 2018.

4.  Koenigshof AM, Beal MW, Poppenga RH, Jutkowitz LA. Effect of sorbitol, single, and multidose activated charcoal administration on carprofen absorption following experimental overdose in dogs. J Vet Emerg Crit Care. 2015;25:606–610.

5.  Fernandez AL, Lee JA, Rahilly L, Hovda L, Brutlag AG, Engebretsen K. The use of intravenous lipid emulsion as an antidote in veterinary toxicology. J Vet Emerg Crit Care. 2011;21:309–320.

6.  Kovalkovičová N, Sutiaková I, Pistl J, Sutiak V. Some food toxic for pets. Interdiscip Toxicol. 2009;2:169–176.

7.  Teichmann-Knorrn S, Doerfelt S, Doerfelt R. Retrospective evaluation of the use of hemodialysis in dogs with suspected metaldehyde poisoning (2012–2017): 11 cases. J Vet Emerg Crit Care. 2020;30:194–201.