Many poisons do not have a specific antidote, or a specific treatment, but close observation and careful supportive care can make all the difference.
If the toxin has been absorbed through the skin, then clipping off the hair in that area and washing the skin with mild soap or detergent will decrease absorption.
If the toxin has been ingested, then vomiting can be induced (see Figure 13.2). Emesis should only be induced after considering a number of factors. Emesis is usually only effective if the substance has been consumed within the past 90 minutes (although for some slowly digested toxins, emesis may still be effective after 2–3 hours). Emesis is contraindicated if the substance is caustic or if aspiration of vomit is likely – such as in an animal with reduced levels of consciousness, an animal that is seizuring or is dyspnoeic.
Apomorphine is commonly used as an emetic in the dog; it is reliable and effective (see Figure 13.3). Vomiting is usually seen within 5–10 minutes following subcutaneous injection. Apomorphine is contraindicated in cats, so xylazine injection is often used. Both apomorphine and xylazine will have some sedative effects. Household agents can be given orally in an emergency (salt, washing soda and washing up liquid) but will not be as effective as recognised injectable emetics, and they should be used with caution in case they themselves cause toxic issues (e.g. salt).
If emesis is ineffective or contraindicated (where the animal is at risk of aspirating vomit due to reduced mentation), then gastric lavage can be used as a means of gastric evacuation. Gastric lavage must be performed under general anaesthesia, with a cuffed endotracheal tube in place. A stomach tube is pre-measured and marked, and then inserted into the stomach. Warm water, at a dose of 10 ml/kg body weight, is then introduced into the stomach, and siphoned out again (see Figure 13.4). The process is repeated until the water runs clear and no more stomach contents are removed (see Practical techniques at the end of the chapter).
Adsorbants such as activated charcoal are useful to reduce further absorption from the gut. They bind the toxin in the gut so it cannot be absorbed, and so passes through the body. Activated charcoal made from vegetable matter is considered the most effective, and is available as powder, tablets, granules or ready mixed as a suspension. Adsorbants are administered orally after emesis (see Figure 13.5), or via a stomach tube after gastric lavage. Administering activated charcoal with dog food does have some reduction in its ability to adsorb toxins, but the reduction in efficacy is unlikely to be clinically significant.
Some commonly encountered toxins have specific antidotes (see Table 13.1). These can be used as soon as they are available. It may not be practical to stock all antidotes, but it is sensible to know which antidotes exist.
|Calcitonin||Vitamin D or calciferol|
4-Methylpyrazole (dogs only)
|Vitamin K1||Anticoagulant rodenticides|
|Methylene blue||Paracetamol, nitrates and chlorates|
Recently, attention has been directed to the use of intravenous lipid emulsions (IVLE) as a tool in managing intoxications with lipophilic drugs, known as ‘lipid rescue’. IVLE is usually used as a source of calories when administering parenteral nutrition. Patients affected by toxins such as local anaesthetics (lidocaine, bupivicaine), permethrin and avermectin parasiticides (e.g. ivermectin, moxidectin) are potentially suitable for therapy with IVLE. The mode of action is uncertain at present, one possibility is that the lipid acts as a ‘sink’ for the lipophilic drugs, so keeping them away from their target receptors and preventing their effects. In cardiotoxic drugs the lipid may provide an energy source to the myocardium to increase performance. An initial bolus is given intravenously, followed by an infusion over 1–2 hours (see Figure 13.6). Potential complications include the return of toxic signs as the lipid is metabolised and the toxin ‘freed’ again. See website documents: Intravenous Lipid Emulsion Monitoring sheet.
By encouraging the body to eliminate a toxin more quickly, we can reduce the risk of continued absorption. Laxatives can be given in addition to adsorbants. This speeds up gut transit times. Magnesium sulphate and sodium citrate are examples.
If the toxin or its metabolites are mainly excreted via the kidneys, then intravenous fluids and diuresis will increase elimination. Creating more alkaline urine with sodium bicarbonate, can help with the excretion of weak acids such as ethylene glycol, via ion trapping.
Peritoneal dialysis is indicated in some cases to aid elimination while also helping to manage consequences of toxicity such as acute renal failure (see Chapter 12).
Treat Known Likely Effects of the Toxin
In cases where the toxin is known, treatment can also be targeted to try to prevent the likely effects. For example, if the toxin is likely to cause gastric ulceration, administer drugs to reduce stomach acid production, and medication to speed the healing of any ulcers that may have already formed.
Metaldehyde is the active ingredient found in slug pellets. Dogs are commonly affected by metaldehyde poisoning, either from eating the pellets from the ground where they have been scattered, or by gaining access to a garden shed and chewing the container. Cases tend to be seen most often in spring or summer when slug pellets are more likely to be used in the garden.
Metaldehyde causes a reduction in inhibition of the central nervous system – because of this effect early clinical signs are restlessness, twitching, tremors and salivation. These clinical signs may be seen as early as 30 minutes after ingesting slug pellets. Later, clinical signs progress to seizures, tachycardia and hyperthermia. If there is no known access to metaldehyde, these symptoms may be confused with other causes of seizures. Sometimes the animal will pass bright green faeces due to the dye in the pellets (see Figure 13.7).