Antiarin
Antiarin is a highly toxic cardiac glycoside found in the sap of the Antiaris toxicaria tree (Upas tree) native to Southeast Asia. Historically, and still occasionally in some regions, the sap is used as an arrow poison.
Properties and Mechanism of Action:
Antiarin functions as a potent inhibitor of the sodium-potassium ATPase pump, an enzyme crucial for maintaining the electrochemical gradients across cell membranes, particularly in heart muscle. By inhibiting this pump, antiarin disrupts the normal flow of sodium and potassium ions, leading to an increase in intracellular sodium and calcium. The elevated intracellular calcium levels enhance myocardial contractility, but at toxic doses, this leads to arrhythmias, fibrillation, and ultimately cardiac arrest.
Toxicity:
Antiarin is extremely poisonous. Even small amounts can be lethal. Symptoms of antiarin poisoning include:
- Muscle weakness
- Nausea and vomiting
- Dizziness
- Cardiac arrhythmias
- Seizures
- Respiratory failure
- Death
The rapid onset and severity of symptoms make antiarin poisoning a serious medical emergency.
Historical Use:
The Antiaris toxicaria tree, from which antiarin is derived, has a long history of use as a source of arrow poison. Indigenous peoples in Southeast Asia would apply the sap to their arrows and darts to hunt animals or for warfare. The effectiveness of the poison meant that even a small wound could be fatal.
Treatment:
Treatment for antiarin poisoning is primarily supportive and aims to stabilize the patient's cardiovascular system. Management may include:
- Gastric lavage (if ingested recently)
- Activated charcoal (to absorb remaining toxin)
- Administration of antiarrhythmic drugs to control heart rhythm abnormalities
- Use of digoxin-specific antibody fragments (Fab fragments) to bind and neutralize the antiarin. However, access to and availability of Fab fragments can be limited.
- Supportive care such as mechanical ventilation if respiratory failure occurs.
Related Compounds:
Antiarin belongs to a class of compounds known as cardiac glycosides. Other well-known cardiac glycosides include digoxin and digitoxin, which are derived from the foxglove plant (Digitalis purpurea) and are used clinically to treat heart conditions such as heart failure and atrial fibrillation, albeit at carefully controlled dosages. While these compounds share a similar mechanism of action with antiarin, they are generally less toxic and have a wider therapeutic window when used appropriately in medical settings.