Nerium species: Oleander

Family

Apocynaceae

Common Names

Oleander, rose laurel, laurel Colorado.

Plant Description

Consisting of a single species with multiple cultivars, Nerium oleander is a native of the Mediterranean area and tropical Asia, and is widely cultivated in the warmer regions of the world. It is a popular landscaping plant because it tolerates relatively dry conditions. Oleander is commonly used in hedges and in highway landscaping.

A perennial evergreen branching shrub that can attain heights of 15 - 20 ft (6 metres), with simple, dark green, glossy, leathery, lanceolate, whorled leaves, with a prominent mid-rib. The fragrant showy flowers are produced terminally on branches, and are funnel shaped with 5 petals, in colors of white, red, or pink (Fig. 285 and Fig. 286). Some cultivars have double petals. Fruits are bean-like seed pods with numerous plumed seeds.

Figure 285. Nerium oleander (flowers and pod).

Figure 286. Nerium oleander.

Toxic Principle and Mechanism of Action

Nerium oleander contains numerous cardenolides and their genins that are concentrated in the leaves, flowers, and seeds [1,2]. Also present in the plant are terpenoids that possibily account for the gastrointestinal irritation seen with oleander poisoning.

The cardiotoxic effect of the oleander cardenolides is similar to that caused by digitoxin and digoxin found in the Digitalis species. The primary action of the cardenolides is on the cell membrane, where interference with normal transport of sodium and potassium ions across the cell membrane occurs allowing an influx of calcium [3]. At low doses, myocardial function may improve, but at high doses cardiac conduction is impaired with resulting arrhythmias, heart block, and death.

A wide variety of animals including humans, dogs, cats, horses, cattle, sheep, goats, llamas, and birds have been poisoned by oleander [4-10].

Risk Assessment

Oleander is a common plant in many gardens and is frequently used in landscaping in tropical and subtropical areas. In temperate climates it is often sold as a potted plant for indoor use. Considering that oleander is one of the most cardiotoxic plants known, and is poisonous to most animals including humans, it should not be planted where it could be a risk to children or household pets. It should not be planted in or around animal enclosures, and the leaves and branches pruned from oleander shrubs should never be fed to animals [11]. Oleander is highly poisonous to birds and therefore should not be included in aviaries [8,11]. Compost made from oleander leaves can result in detectable but low levels of the glycoside oleandrin in plants mulched with the oleander compost [12].

Clinical Signs

Excessive salivation, vomiting, and diarrhea are commonly seen initially in dogs, cats and most other species poisoned by oleander. The diarrhea may contain blood. Within a few hours of ingesting the plant, cardiac signs develop including weakness, depression, irregular pulse, bradycardia, and increased respiratory rate. Electrocardiographically, S-T depression, bradycardia, extrasystoles, and various dysrhythmias will be apparent. Hyperkalemia may or may not be present. Depending on the quantity of the cardenolides ingested, animals may exhibit signs of depression and heart irregularity for many hours before recovering or they may die suddenly due to cardiac arrest.

At postmortem examination, there are generally no specific lesions present. Animals that survived for several days often have necrosis of the myocardium. A diagnosis of oleander poisoning can be made by finding the distinctive leaf parts in the animal’s stomach contents, and by detection of the cardenolides in the stomach contents using high pressure liquid chromatography (HPLC) methods [13]. Successful treatment of oleander poisoning depends on early recognition of the toxicity.

Induction of vomiting, gastric lavage, and/or the oral administration of activated charcoal is appropriate for removing the plant and preventing further absorption of the toxins. Cathartics may also be used to help eliminate the plant rapidly from the digestive system. Serum potassium levels should be closely monitored and appropriate intravenous fluid therapy initiated as necessary. Phenytoin, as an anti-arrhythmic drug effective against supraventricular and ventricular arrhythmias, can be used as necessary. Similarly, atropine and propanalol have been used. The use of commercially available digitalis-specific antibody (Digibind - Burroughs Wellcome) may be a beneficial in counteracting the effects of the cardenolides [14-16].