Plants Toxic to Pets
Susan E. Yohn, DVM, MS, DABVP-Canine/Feline, DACVIM
Dogs and cats are natural diggers and chewers and may ingest leaves, bulbs or flowers from common garden plants. Fortunately, while there are many species of garden plants, only a small percentage are truly poisonous to pets. While the majority of plant toxins result in gastrointestinal signs, a few plant toxins can be life threatening. It is important for the veterinary team to be aware of the most common garden plants that can be toxic to pets, the toxin involved, clinical signs and therapy if ingestion is suspected.
Tulips and Hyacinths
These flowering bulbs contain allergenic lactones called tuliposide A and B. Tuliposides are in all parts of the plants but most concentrated in the bulbs, which also contain calcium oxalate crystals. The greatest danger is to dogs that tend to dig up and chew the bulbs. Clinical signs include hypersalivation, vomiting, diarrhea and depression. With large amounts of bulb material ingested, tachycardia and dyspnea can be seen. There is no antidote, and therapy is supportive including rinsing out the mouth, fluid therapy, antiemetics and GI protectants. Blood pressure and ECG monitoring, anticonvulsants or antiarrythmics may be necessary in severe cases.
These flowers contain lycorine, an alkaloid with emetic properties. Ingestion of the bulb, plant or flower can cause clinical signs including vomiting, diarrhea, abdominal pain, cardiac arrhythmias, hypotension, respiratory depression and possibly CNS signs (tremors, seizures). Severity of the clinical signs are related to the amount of plant material ingested. As with tulips and hyacinths, there is no antidote, and supportive care is similar to that for tulip or hyacinth ingestion based on the clinical signs of the pet at presentation.
Foxglove and Lily of the Valley
These are two of several garden plants that contain cardiotoxic cardenolides or bufaliendolides. These are naturally occurring cardiac glycosides related to digoxin. All parts of the plants are toxic; even water from a vase that holds flowers from these plants can be toxic. The toxins block the function of the cellular ATP Na-K pump which causes increased intracellular sodium and decreased intracellular potassium. Cardiovascular signs (brady or tachyarrhythmias, AV block, asystole), hyperkalemia, gastrointestinal signs (hypersalivation, vomiting), or central nervous system signs (mydriasis, tremors, seizures) may be seen. Diagnostics for a pet suspected of ingesting these plants should include renal and electrolyte status, ECG and blood pressure. Therapy includes fluids and colloid support for blood pressure, antiemetics, antiarrythmics and anticonvulsants. The antidote, digoxin-specific Fab fragments, is available on the human market but is cost prohibitive.
Azaleas and Rhododendrons
These common shrubs contain grayanotoxins that bind to sodium ion channels in cell membranes of cardiac and skeletal muscle cells. Sodium transport is blocked and the cell remains depolarized. All parts of the plant are considered poisonous. Although fatal toxicosis is rare in humans, ingestion of only small amounts of leaves in dogs or cats can cause severe symptoms including coma or possible death. Symptoms occur after a latent period of minutes to three hours and include hypersalivation, vomiting, weakness and paresthesia in the extremities. With large amounts of plant ingestion, symptoms can include loss of coordination, progressive muscular weakness, bundle branch block and/or ST-segment elevations, hypotension and profound bradycardia. Fluid and colloid support, antiemetics, atropine therapy, vasopressors and other agents are used to manage clinical symptoms.
Lilies (Lilium) and Daylilies (Hemerocallis)
There are toxic and benign lilies found in the garden or in floral arrangements in the home. Calla and Peace lilies contain insoluble oxalate crystals that can cause minor signs of tissue irritation to the mouth, tongue, pharynx and esophagus. Drooling is usually the presenting clinical sign, and no extensive medical management is necessary.
The “true” toxic lilies include Tiger, Asiatic, Easter, Japanese Show, and Day lilies. The toxin in lilies has not been identified, but all parts of the plant including the pollen and water in a vase that has held the flowers or foliage are toxic to cats. Dogs and humans are not susceptible to this toxin, but even small ingestion of leaves or petals can result in severe kidney failure in cats. Clinical signs are seen within hours of ingestion and include vomiting, depression and anorexia. Acute renal failure can progress to anuric renal failure in 1 to 3 days. Lab profiling shows severe azotemia, with epithelial casts on urinalysis, proteinuria and glucosuria. Treatment includes decontamination (induce vomiting, activated charcoal), antiemetics, gastroprotectants and IV fluid diuresis. Peritoneal or hemodialysis is appropriate for cats with anuric renal failure. Early and aggressive decontamination and fluid therapy is important in successful management. Subcutaneous fluids are not adequate for therapy in lily toxicosis. If supportive care is initiated after 18 hours of ingestion or if anuria develops, prognosis is poor.
There are some common houseplants that need to be considered toxic. The Shamrock plant, sold around St. Patrick’s Day, contains soluble calcium oxalates which can cause gastrointestinal signs. The oxalates can be absorbed and bind to systemic calcium resulting in hypocalcemia and deposition of calcium oxalate crystals in the kidneys. The likelihood of this toxicity is low, but dehydrated pets or those with renal insufficiency may be more at risk. Therapy is rehydration and diuresis. Easter lilies, which have already been discussed, are commonly brought into the home during the Easter holiday season and should be avoided in homes with cats. Kalanchoe plants, sold as flowering houseplants, contain cardiac glycosides like their cousin, foxglove. All of the plant is considered toxic with clinical signs and treatment the same as discussed for foxglove. This is another house plant that should be avoided in homes with dogs and cats.
This is not an exhaustive list of toxic plants. When possible toxic plant ingestion is suspected, supportive care should be considered while information is obtained to verify the exact plant species consumed. Local horticulturists or florists may serve as good resources to verify plant identification. While the majority of plant toxins result in gastrointestinal signs, a few plants toxins can be life threatening. Whenever toxic plant ingestion is suspected, Animal Poison Control (ASPCA) should be consulted (888.426.4435) to more specifically direct medical management to ensure a good outcome for the pet.