ABSTRACT
Toxic Principle and Mechanism of Action Yews contain a variety of toxins including cyanogenic glycosides, taxane derivitives, ephedrine, irritant oil, and molting hormone.1,2 Only the nitrogenous taxane alkaloids known as taxines are associated with the cardiotoxic effects of the Taxus species. Taxine B is more toxic than taxine A, and the proportions of the taxines varies depending upon the species of Taxus.3,4 Taxine B causes decreased cardiac contractility and marked slowing of atrial and ventricular rates. This effect is mediated through taxine B’s inhibition of sodium, potassium, and calcium channels in cardiac muscle.5 All parts of the plant are toxic except for the ripe redorange aril. The seed itself is toxic. The plant also appears to be more toxic in winter.6 Taxus canadensis has the lowest concentrations of taxines and probably has little potential for toxicity. All domestic animals including birds are
detoxify taxines.12
