Over their evolution, plants have developed numerous toxic agents to protect themselves from being eaten; many of these substances are extremely poisonous. Even plants that are considered nontoxic-that is, ingestion should not cause serious systemic signs-may result in vomiting and other gastrointestinal disorders. Plants help cozy up a living space, but pet owners should be extra careful when choosing greenery. The plants discussed in this article are considered to be among the most toxic for dogs and cats; serious illness and death can result from consumption of relatively small amounts. These plants are commonly found in the home or yard.

Lilies

Toxicosis occurs only in cats.

Principal Toxin – unknown

All parts of the plant are toxic (even the pollen).

Causes acute renal failure secondary to acute tubular necrosis.

Clinical Signs: initially, vomiting, anorexia, and lethargy starting within hours of ingestion; vomiting may subside by 12 hours.

Renal values (blood urea nitrogen, creatinine, and phosphorus) and potassium levels begin to increase by 24 to 72 hours.

Renal epithelial tubular casts and glucosuria can be seen within 18 hours.

Prognosis: guarded with delayed onset of treatment (24 hours or greater) and in presence of oliguria/anuria.

Renal function can return but may take weeks; chronic renal failure may be sequela.

Azalea

Toxin blocks the sodium channel in cells; principally affects muscle and nerve cells.

Whole plant is toxic.

Clinical Signs: predominately vomiting, starting within a few hours of ingestion; diarrhea is rare.

Aspiration pneumonia is a possible sequela.

Cardiac arrhythmias are possible.

Neurologic signs may include depression, ataxia, weakness, and seizures.

Prognosis: good if seizures or aspiration has not occurred.

Yews

Often used as hedges; can grow up to 75 feet high depending on species, but often are trimmed.

Principal Toxin: various taxane derivatives or taxines, which are negative inotropes and chronotropes

All parts of the plant are toxic; deaths following chewing on branches have been reported in dogs.

Clinical Signs: death may be so rapid that there are no signs.

Vomiting and neurologic signs are most common in dogs, although bradycardia can also be seen.

Prognosis: guarded if signs appear

Autumn Crocuses

Colchicum autumnale (autumn crocus, meadow saffron); Colchicum speciosum(showy autumn crocus)

Occur throughout the United States; leaves, which grow from the base, can reach about a foot long; flowers appear after the leaves have died in the autumn.

Principal Toxin: colchicine and similar alkaloids which prevent cell division

All parts of the plant are toxic but highest concentration of the toxin is found in the flower, the corm, and the seeds.

Clinical Signs: signs may take 12 to 24 hours to develop and initially occur as hypersalivation, depression, vomiting, milky or bloody diarrhea, and abdominal pain.

Progress to weakness, paresis, and collapse.

Multiple organ failure can occur.

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Prognosis: guarded

Foxglove

Stems can range from 1 to 6 feet tall with 1- to 2-inch conical flowers.

Principal Toxin: Cardenolides, principally digitalis, a cardiac glycoside

All parts of the plant are toxic, but highest concentrations are found in the flowers, fruit, and immature leaves.

Dried plant matter retains toxicity.

Clinical Signs: initially, gastrointestinal signs are present.

Cardiac arrhythmias of any type can occur.

Prognosis: good, unless intractable arrhythmias or hyperkalemia develops.

 

Lily of the Valley

Plant has broad, erect leaves (4 to 8 inches) with small, bell-shaped flowers.

Principal Toxin: Cardenolides, potent cardiotoxins

Toxin is concentrated in the roots, but all parts of the plant are toxic.

Clinical Signs: initial signs are gastrointestinal with vomiting and hypersalivation; diarrhea is less common.

Cardiac signs include bradycardia and other arrhythmias.

Seizures may also occur.

Death may be sudden without any prior signs.

Prognosis: good, unless intractable arrhythmias or hyperkalemia develops.

Oleander

Nerium oleander, also known as laurel rosa, laurel blanco, laurel colorado, rosa laurel

Not native to North America; found in the South and California.

Frequently planted as roadside hedge or backyard ornamental; can grow from 7 to 20 feet tall.

Principal Toxin: Cardiac glycosides

Toxicity often due to ingestion of dead/dry leaves; green leaves are bitter and less likely to be eaten; when the leaf dies, the sugar moiety is released from the cardiac glycoside, which improves palatability.

Clinical Signs: initially vomiting and diarrhea (the latter may contain blood)

Signs may progress to cardiac arrhythmias of any type (similar to digitalis toxicity).

Prognosis: good with aggressive therapy.

Yesterday, Today, and Tomorrow

Brunfelsia australis. Photograph shows B. grandiflora; flowers are identical to those of B. australis but appear in clusters whereas in B. australis they are spread out over plant.

Ornamental found mainly in the South; grows as a shrub or small tree.

Principal Toxin: Brunfelsamidine, a neurotoxin that causes seizures

All parts of the plant are toxic.

Clinical Signs: coughing, gagging, and nystagmus can be seen within minutes to hours; tremors and seizures, usually characterized by extensor rigidity (may resemble those of strychnine toxicity)

Prognosis: guarded; signs can last for days and complete recovery may take weeks.

Castor Bean

Ricinus communis (castor bean plant); also known as castor oil plant, mole bean, wonder tree

Occurs in the South, Southwest, and California; may be wild or cultivated for castor oil; plants can stand 3 to 14 feet tall and have large leaves (12 inches or greater).

The beans are used as decorative beads.

Principal Toxin: Ricin, a glycoprotein

Blocks protein synthesis, leading to cellular death.

Is present in all parts of the plant but most concentrated in the beans.

Highly toxic; a single bean can kill a dog.

The outer coating of the bean must be ruptured (chewed) to release the ricin.

Clinical Signs: may take up to 24 hours to appear; initial signs include vomiting and often bloody diarrhea, abdominal pain, weakness, and ataxia.

Hemoconcentration, leukocytosis, and elevated liver enzymes can be seen on clinical laboratory testing.

Cycad Palms

Many species, but principally sago palm (Cycas revoluta) and fern palm/false sago palm (C. circinalis); size varies with species and can range from 6 to 30 feet tall with long leaves (up to 9 feet).

Used as ornamental plants in Florida and occasionally in California; can be houseplants in northern climates.

Sago palms are available as bonsai trees.

Principal Toxin: Cycasin, a glycoside, yields methylazoxymethanol after bacteria metabolism

Cycasin is present in the whole plant, but concentration is highest in the seeds; ingestion of as few as 1 to 2 seeds can cause severe clinical signs and death.

Clinical Signs: initially, vomiting, possibly beginning within a few minutes of ingestion of the seeds; vomiting may last for hours.

Hypersalivation and polydipsia can be seen.

Over the next few days, anorexia, diarrhea or constipation, hepatomegaly, and icterus are seen.

Neurotoxic effects can be seen but these may be secondary to hepatic failure.

Clinical pathology includes thrombocytopenia, bilirubinemia, elevated hepatic enzymes, and azotemia.

Prognosis: poor once hepatic necrosis has occurred.