Toxic effects of the vitamin K family are manifested mainly as hematological and circulatory derangements. In dogs, Heinz body hemolytic anemia (denatured globin chains within red blood cells) was reported at dosages of 26 mg menadione per kg (11.8 mg per lb) (Fernandez et al., 1984). Not only is species variation encountered, but profound differences are observed in the ability of the various vitamin K compounds to evoke a toxic response (Barash, 1978). The naturally occurring forms of vitamin K, phylloquinone and menaquinone, are nontoxic at very high dosage levels. The synthetic menadione compounds, however, have shown toxic effects when fed to humans, rabbits, dogs and mice in excessive amounts. The toxic dietary level of menadione is at least 1,000 times the dietary requirement (NRC, 1987). Menadione compounds can safely be used at low levels to prevent the development of a deficiency but should not be used to treat a hemorrhagic condition.
The LD50 for a single parenteral dose of menadione or its water-soluble derivative is in the range of 75 to 200 mg per kg (34 to 91 mg per lb) of body weight for chicks, mice, rats, rabbits and dogs, and the LD50 for a single oral dose is 600 to 800 mg per kg (273 to 364 mg per lb) of body weight, at least for chicks and mice. Specifically for dogs, the LD50 was 100 to 150 mg per kg (45.5 to 68.2 mg per lb) body weight (Richards and Shapiro, 1945). Vitamin K toxicity data for cats are not available (NRC, 1987).
