Milkweed Poisoning in Dogs

Plants in the Asclepias genus, more commonly known as milkweed plants, are herbaceous perennials with complex flowers. Plants in the Asclepias genus contain several toxins throughout the plant, including galitoxin and cardiac glycosides. These compounds can make the consumption of milkweed plants toxic in moderate to large amounts.Certain insects have developed to dine on the milkweed plant, most notably the caterpillar of the monarch butterfly. The constant ingestion of milkweed sap during the caterpillar stage can also make both the caterpillar and subsequent butterfly noxious as well.

Milkweed plants contain both galitoxin and cardiac glycosides in all parts of the plant, although they concentrate in the sap. Ingestion of milkweed should be treated as an urgent matter.

The symptoms of milkweed poisoning are caused by a combination of galitoxin and cardiac glycosides. If you suspect that your pet has eaten milkweed, contact your veterinarian as soon as possible for a definitive diagnosis and treatment plan. 

• Cardiac arrhythmias
• Collapse
• Decreased heart rate
• Depression
• Diarrhea
• Drooling
• Hyperkalemia (high levels of potassium in blood)
• Increased heart rate
• Loss of appetite
• Lethargy
• Nausea
• Nervousness
• Seizures
• Sudden death
• Tremors
• Unsteady gait
• Vomiting
• Weakness

Types

There are many species of milkweed, known by names as diverse as butterfly weed, blood flower, and pleurisy root. Although all plants in the Asclepias genus are toxic, the levels of toxic compounds in each plant can be quite different from one species to another. The species that display narrow leaves are much more likely to cause neurotoxic symptoms to develop, whereas the broader leaved varieties tend to induce the cardiac related signs and symptoms. Some examples of species with narrow leaves would include the Asclepias verticillata, or whorled milkweed and the Asclepias linaria, or pine needle milkweed. Asclepias erosa, also known as desert milkweed, and Asclepias cordifolia, known as heart-leaf milkweed, would be considered broad-leaved species.

The primary toxin in milkweed is galitoxin, which is responsible for most of the tremors, nervousness, and seizures.The milkweed plant also has high concentrations of cardiac glycosides in its sap. These organic compounds are known to alter the rhythm of the heart by acting on the force of the cardiac muscle itself. Cardiac glycosides have been for centuries both as a treatment method for those with certain cardiac disorders and as a potent poison.

In addition, the caterpillar of the monarch butterfly dines exclusively on the sap of the milkweed plant, rendering both the caterpillar and butterfly mildly toxic as well.

If you catch your pet consuming milkweed plant, signs of intoxication combined with the identification of the plant should be enough to make a preliminary diagnosis. Your veterinarian will ask for more information about how much the patient ingested and how long ago the ingestion occurred. If consumption of the item was not witnessed, symptoms would be likely to prompt questions regarding any opportunistic eating that was witnessed or suspected in addition to any prescribed prescriptions or dietary supplements that have been administered to your dog. Other medications are particularly important when dealing with milkweed toxicity as drugs such as beta-blockers, steroids, and some chemotherapy agents may have negative interactions with cardiac glycosides. A biochemistry profile is likely at this time, as well as a complete blood count and urinalysis. The levels of magnesium and potassium that are present in the blood will be expressly noted. There are blood tests available to detect the presence and amount of the cardiac glycosides in the circulatory system. The cost of these methods, unfortunately, limits their accessibility for veterinary diagnosis.

If it has been just a short time since ingestion, your veterinarian may instruct you on the proper method to induce vomiting in your dog. If your pet is still conscious when you reach your veterinarian's office, and not actively vomiting, activated charcoal is likely to be administered in an attempt to soak up as many of the toxins as possible before they disperse into the bloodstream. Some cases of poisoning with cardiac glycosides will require that your pet undergoes a gastric lavage. Supportive measures for poisonings will usually include IV fluids for dehydration and combinations of sugars and electrolytes to adjust for any imbalances. Calcium is known to enhance the effects of cardiac glycoside so should be avoided as an additive to the IV fluids. Supplemental potassium can also be risky as it has been known to induce hyperkalemia. Antiarrhythmic drugs such as atropine sulfate, lidocaine, or procainamide may be utilized to regulate the heart. Although digoxin-specific antibodies have had some success in treating toxicity in humans, it has not proven as effective in other animals such as canines and is rarely recommended. Experimental treatments using injections of fructose have also been completed to reduce serum potassium levels and heart irregularities.

The patient usually succumbs or begins the recovery process within 24 hours from the emergence of the first symptoms, and supportive measures are a key factor in mortality. Ensuring that a quiet and calm setting for the recuperating patient to return home to will help speed recovery. This is of particular importance when cardiac glycoside poisoning is involved to avoid further stress on the heart. Ample quantities of fresh water should be made available to avoid dehydration Canines recovering from anesthesia such as given for a gastric irrigation may have coordination difficulties at first, and are often initially confused and disoriented. Isolation from children and other pets may be advised until the medication has fully cleared your companion’s system.