Agent	Dose	Comments
Soda crystals (washing soda)	1 crystal	Place on tongue at back of mouth Emesis usually within 10 minutes Can be repeated NB. Not caustic soda (sodium hydroxide)
Syrup of ipecacuanha (7%)	D: 1–2 ml/kg p.o. C: 3.3 ml/kg p.o.	Emesis usually within 30 minutes Can be repeated once Bitter taste therefore poor compliance
Hydrogen peroxide (3%)	D, C: 1–3 ml/kg	Emesis usually within 10 minutes Can be repeated once Care to avoid aspiration
Table salt (sodium chloride)	Not recommended	Unreliable May induce or exacerbate hypernatraemia with potentially severe consequences Ad lib access to water imperative if used

C, cats; D, dogs.

Clinical Tip

• It is very important to make sure that soda crystals (washing soda) are used for emesis, as owners have inadvertently administered caustic soda (sodium hydroxide) instead. This is very harmful following ingestion, causing severe injury to the oropharyngeal and oesophageal mucosa with potentially fatal consequences (Figure 30.1).

Figure 30.1 Severe oral cavity injury in a dog inadvertently given caustic soda by her owners for emesis. Severe mucosal injury extended all the way down the oesophagus.

(Photograph courtesy of Tammy Ford)

General Clinical Approach

See Box 30.5.

History

Clinical Tip

• In a patient presents with severe clinical signs (e.g. seizures, severe muscle tremors) history-taking should not be prioritized over initial stabilization, especially as specific antidotes are not available for the majority of poisons to which dogs and cats are exposed. Ultimately treatment is directed at the patient and not the poison.

All the information in Boxes 30.1 and 30.2 should be obtained at the appropriate time. In some emergency patients, clinical signs and progression are compatible with possible intoxication without an immediately suggestive history. In such cases, the owner must be carefully and thoroughly questioned to establish whether a potential source of poison exists that the owner has not considered.

Initial management of ingested poisons

As for all emergency patients, a major body system (cardiovascular, respiratory, neurological) examination (see Ch. 1), including measurement of rectal temperature, should be performed and immediate measures taken to correct potentially life-threatening problems. Intravenous fluid therapy (see Ch. 4) may be required to correct hypovolaemia and/or dehydration. Fluid therapy is also indicated in the management of poisons that are nephrotoxic (e.g. nonsteroidal antiinflammatory agents) and those that are largely dependent on renal excretion. Oxygen supplementation is indicated in patients with respiratory compromise, for example from aspiration following vomiting, and in the context of certain poisons such as carbon monoxide.

Emergency database

An emergency database (see Ch. 3) for the intoxicated patient should consist of the following if possible:

• Manual packed cell volume (PCV) and serum total solids (TS)

• Blood glucose, electrolyte, urea and creatinine concentrations

• Peripheral blood smear examination

• Electrocardiogram (ECG)

• Noninvasive blood pressure (NIBP).

Additional tests that may be indicated at the appropriate time in certain cases include acid–base analysis, urinalysis (e.g. oxalate crystals in ethylene glycol poisoning) and calcium measurement (e.g. hypocalcaemia may occur in ethylene glycol poisoning). Abdominal radiographs taken at the appropriate time may reveal ingestion of items containing heavy metals or certain enteric-coated or sustained-release drug formulations. Routine haematology and biochemistry profiles may become indicated as case management progresses and may also identify pre-existing conditions that may have implications with respect to management of individual patients.

Treatment of seizures and muscle tremors

A variety of poisons include neurotoxicity amongst their mechanisms of action – examples include metaldehyde, pyrethroids, strychnine, caffeine, theobromine, organophosphates and tremorogenic mycotoxins. Seizures and/or muscle tremors are common signs of poisoning requiring symptomatic treatment (see Ch. 24).

In patients intoxicated with tremorogenic poisons (e.g. metaldehyde, permethrin), it can be difficult to differentiate severe muscle tremors from seizure activity. However, if the poison in question is known to be one associated with severe tremors or sufficient clinical suspicion exists, the use of methocarbamol may be indicated and may avoid the need for anaesthesia. This is a centrally acting muscle relaxant related to guaiphenesin whose precise mechanism of action remains unclear. The manufacturer’s recommended dose in dogs and cats is 44–220 mg/kg i.v. with a typical upper limit of 330 mg/kg in a 24 hour period. However, to the author’s knowledge, an injectable preparation of this agent is not currently available in the United Kingdom. In the absence of methocarbamol, the management of patients with tremors is the same as for those with seizures.

Clinical Tip

• The aim of treatment is to achieve adequate control of tremors; complete abolition of tremors is neither likely nor necessary and may require excessive drug administration.

Hyperthermia is a potentially serious development in patients suffering from seizures or muscle tremors. Hypothermia may also occur following bathing or sedation. Close monitoring of rectal temperature for either development and appropriate intervention (see Chs 16 and 17) is therefore required.

Gastrointestinal decontamination (GID)

Toxin exposure is usually via ingestion and gastrointestinal decontamination (GID) is frequently indicated. This consists of emptying of the stomach followed by administration of an adsorbent to minimize absorption of any poison remaining in the gastrointestinal tract.

Gastric emptying

In the absence of contraindications (see Box 30.4), induction of emesis is the most expeditious means to empty the stomach; feeding a small meal first may increase the effectiveness of this approach. The author has performed gastric emptying up to 4–6 hours following ingestion with some good results. Drugs used to induce emesis are summarized in Table 30.2.

Table 30.2 Drugs used to induce emesis

Drug	Dose	Comments
Apomorphine	D: 0.04–0.1 mg/kg s.c., i.m., ocular	Drug of choice, emesis usually in 5–15 min Centrally acting Sedation, respiratory depression, ataxia, protracted vomiting possible (rare) Naloxone reverses sedative but not emetic effects Ocular route: apply to conjunctival sac; lavage thoroughly following emesis to minimize drug absorption; highly dependent on compliance
Apomorphine	C: 0.01–0.02 mg/kg s.c., i.m.	Use lowest possible dose Not recommended by some due to possible significant sedation Naloxone reverses sedative but not emetic effects
Medetomidine	C: 20 µg/kg i.m., i.v.	Alpha₂-adrenergic agonist Use atipamezole (50 µg/kg i.m.) to reverse effects once emesis has occurred Use very cautiously due to potential cardiorespiratory depression
Xylazine	C: 0.4–0.5 mg/kg i.m., s.c.	Alpha₂-adrenergic agonist Atipamezole may reverse effects Use very cautiously due to potential cardiorespiratory depression

C, cats; CNS, central nervous system; D, dogs; i.m., intramuscular; i.v., intravenous; s.c., subcutaneous.

Activated charcoal

Activated charcoal acts as an adsorbent binding to toxins and allowing their passage through the gastrointestinal tract while preventing or minimizing further systemic absorption. It is typically administered once gastric emptying has been performed and should be given as soon as possible. If an emetic has been employed for gastric emptying, enough time must be allowed for the emetic effects to subside before activated charcoal is administered. In some cases activated charcoal is administered initially via stomach tube at the end of gastric lavage. The recommended dose in dogs and cats is 1–5 g/kg to be repeated as necessary (typically every 4–6 hours) until black faeces are detected. Doses up to 8 g/kg have been used. Activated charcoal is often successfully administered in food to dogs. However, compliance is likely to be much poorer in cats. Various proprietary preparations are available with accompanying dosing guidelines, including powdered formulations (e.g. BCK Granules^®, Fort Dodge) that can be added to food or made into a slurry and administered by mouth, and suspensions (e.g. Charcodote^®, Pliva Pharma Ltd).

Different substances are bound to different degrees by activated charcoal. However, unless contraindicated, the use of activated charcoal in almost all cases of oral poisoning is probably reasonable and may also help following topical poisoning (see below). Activated charcoal should not be used following ingestion of caustic or corrosive substances, in patients that are vomiting or seizuring, or where there is any possibility of gastrointestinal perforation. Vomiting and constipation following administration of multiple doses are the main complications reported.

Gastric and colorectal lavage

In patients in which induction of emesis is contraindicated or unsuccessful, gastric lavage may be appropriate for gastric emptying (see p. 296). However, it is contraindicated following ingestion of caustic or corrosive substances and where the risks of general anaesthesia are considered unacceptable.

In some cases (e.g. metaldehyde poisoning), following gastric lavage, the author will perform additional lavage via a stomach tube inserted as proximally as possible per rectum. Colorectal lavage is continued until clear fluid is returned and activated charcoal suspension is then instilled. The anus may be plugged with a swab for example for a short period of time to minimize leakage of the activated charcoal.

Specific Poisons

Pyrethrins and pyrethroids

Theory refresher

Pyrethrins are naturally occurring insecticidal esters of chrysanthemic acid and pyrethric acid extracted from the Chrysanthemum cinerariaefolium plant; pyrethroids (e.g. permethrin) are synthetic pyrethrins. Many topical and household insecticidal preparations containing these compounds are marketed for the control of flea and lice infestations amongst others in dogs and cats. These preparations are widely available from a variety of outlets.

Clinical Tip

• Synthetic pyrethroid insecticides are now most commonly used in small animal patients as topical spot-on formulations and the accidental or misguided inappropriate use of canine products on cats is the most commonly encountered cause of poisoning. In addition, cats may directly contact or lick the product once applied to a dog in the same household.

Toxic dose

The toxic dose for permethrin in cats is unknown. Dermal application of 100 mg/kg permethrin may prove life-threatening if untreated.

Mechanism of toxicity

Pyrethrins and pyrethroids alter the kinetics of neuronal sodium channels causing repeated nerve firing. In addition, some of these compounds may also inhibit gamma aminobutyric acid (GABA) receptors, resulting in hyperexcitability of nervous tissue. Glucuronidation is one pathway involved in the metabolism of some of these compounds and glucuronyl transferase deficiency may be part of the explanation for the apparent sensitivity of cats to pyrethroids.

Oral exposure

Oral exposure should be treated by gastrointestinal decontamination if appropriate, including activated charcoal if patient compliance allows. Pyrethrins and pyrethroids are highly fat soluble and low fat foods should therefore be fed in the short term to reduce further absorption.

Case example 1

Presenting Signs and Case History

A 1-year-old female neutered domestic short hair cat (2.5 kg) presented 3 hours after topical application of a spot-on preparation containing 744 mg permethrin per millilitre. The preparation used was registered for use in dogs only but the owner had thought it would be safe to administer half of the pipette to the cat. The cat had developed clinical signs within 1 hour of administration and at the time of presentation was showing severe muscle tremors.

Clinical Tip

• Clinical signs usually develop within a few hours of exposure. Minor and usually self-limiting signs include hyperaesthesia, hypersalivation, ataxia, mydriasis, paw flicking and ear twitching. These signs may be accompanied by other nonspecific signs such as lethargy or transient vomiting and diarrhoea.

• Severe neurotoxicity resulting from excessive exposure may result in marked depression, ataxia, potentially violent muscle tremors, seizures and death. Protracted gastrointestinal signs may also occur.

Case management

Diazepam (5 mg) was administered per rectum to facilitate intravenous catheter placement and blood was obtained via the catheter for an emergency database to be performed; this was found to be unremarkable. Major body system examination was unremarkable except for the muscle tremors that were less severe but still marked.

Intravenous fluid therapy was commenced and anaesthesia was induced using propofol and maintained using isoflurane. The cat was washed thoroughly in a mild detergent and dried before being recovered with an Elizabethan collar in place. Muscle tremors were apparent in recovery but of lesser severity and a single intravenous bolus of midazolam (0.2 mg/kg) was administered.

Tremors resolved fully over the next 24 hours, during which time vital parameters, in particular temperature, were monitored closely and appropriate supportive and nursing measures instituted.

Permethrin dosage in this case was approximately 150 mg/kg.

Clinical Tip

• The prognosis for full recovery is reasonable despite severe poisoning in animals receiving early and appropriately aggressive intervention; neurotoxicity is fully reversible. In severe cases clinical signs may take 72 hours or more to resolve.

Metaldehyde

Theory refresher

Metaldehyde is a cyclic tetramer of acetaldehyde that is commonly used as a pesticide against slugs and snails (molluscicide). Commercial pellet preparations usually contain 1.5–8% metaldehyde w/w (see Box 30.3) in a cereal base. The pellets are often blue or green in colour and the cereals and other additives make slug/snail baits palatable to dogs. Cats as usual are more discerning and metaldehyde poisoning has only been reported in a few cases. Liquid preparations containing higher concentrations of metaldehyde are also available, as are granular and powdered preparations. Metaldehyde baits sometimes contain additional herbicides and pesticides, most commonly carbamate insecticides.