- Kalmia is a large shrub or small tree with smooth, elliptical, alternate or whorled leaves. Showy white or pink flowers with fused petals arise in the leaf axils of the upper stems. The plant has green leaves all year in moderate climates and is primarily a threat to browsing animals like sheep, goats and, less commonly, cattle and horses.
- Geographic range
- Kalmia grows wild in the woods and mountain foothills of the southeastern, Appalachian and mid-Atlantic coastal states. Some species are found in the Pacific coastal states and in temperate areas along the Pacific Coast north to Alaska.
- Toxic principle
- Andromedotoxins (grayanotoxins) are water-soluble diterpenoid compounds. Leaves and flower nectar (including honey made from plant nectar) are sources of the toxin.
- As little as 3 ml nectar/kg body weight or 0.2% of the body weight as leaves may be toxic or lethal.
- Mechanism of toxicologic damage
- Andromedotoxins bind to and modify the sodium channels of cell membranes, leading to prolonged depolarization and excitation. Modification of the sodium channels favors calcium movement into cells and results in a positive inotropic effect similar to that of digitalis.
- Clinical signs
- Salivation and a burning sensation in the mouth are followed by emesis, diarrhea, muscular weakness and impaired vision. Bradycardia, hypotension (caused by vasodilation) and atrioventricular block are serious cardiovascular effects that may be lethal. Dyspnea, depression, and prostration develop, and death may occur within 1-2 days. Ruminants often bloat. Aspiration pneumonia can develop secondary to emesis.
- Laboratory diagnosis
- Generally non-specific findings.
- Lesions are non-specific
- Detection of leaves in GI tract may assist in diagnosis.
- Detoxification. Emesis is used where appropriate. Activated charcoal should be administered repeatedly the first day.
- Supportive therapy. Fluid replacement therapy and respiratory support may be necessary. Atropine is recommended for severe bradycardia. Isoproterenol or sodium channel blockers (e.g., quinidine) may be used to treat heart block.
Honey made from the plants has been reported to cause cardiac arrhythmias, emesis, mild paralysis and convulsions in humans and is known as “mad honey”.
Read more in the Poisonous Plants of Pennsylvania Publication