Harmful effects of nicotinic acid occur at levels far in excess of requirements (NRC, 1987). Nicotinic acid and niacinamide tolerance in cats has not been determined.
Chen et al. (1938) reported the toxicity of nicotinic acid for dogs. They found that repeated oral administration of 2 g per day of nicotinic acid (133 to 145 mg per kg or 60.5 to 65.9 mg per lb of body weight) produced bloody feces in a few dogs. Convulsions and death followed. Doses of nicotinic acid as great as 0.5 g per day, which is about 36 mg per kg (16.4 mg per lb) body weight, produced slight proteinuria after eight weeks. Nicotinamide is two to three times more toxic than the free acid (Waterman, 1978).
