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PHARMACOLOGICAL ACTIVITIES - TOXICOLOGY - DRUG INTERACTIONS

Niacinamide [Vitamin B ] (C H N O)
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Dogs and cats derive most of their energy from oxidation-reduction (redox) reactions, which
are processes involving the transfer of electrons. As many as 200 enzymes require the niacin
coenzymes, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide
phosphate (NADP), mainly to accept or donate electrons for redox reactions. NAD functions
most often in energy producing reactions involving the catabolism of carbohydrates, fats,
proteins, and alcohol. NADP functions more often in anabolic reactions, such as in the synthesis
of all macromolecules, including fatty acids and cholesterol (Brody, 1999).

A vitamin B deficiency is characterized by loss of appetite, fatigue, apathy and mouth ulcers,
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diarrhoea, emaciation and pruritic dermatitis of the hind legs and ventral abdomen. Cats
need more niacin than dogs. Dogs are able to synthesize nicotinamide endogenously from
tryptophan; cats do not produce any measurable quantities. Cats possess all the enzymes of the
pathway of niacin synthesis, but the activity of picolinic carboxylase is extremely high, precluding
any measurable synthesis of nicotinic acid (NRC, 2006; Ettinger & Feldman, 2000a).

TOXICOLOGY Toxicity for vitamin B has not been documented in dogs and cats when administered orally in therapeutic doses.
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However, it has been reported that repeated oral administration of 2 g/day of nicotinic acid produced bloody
feces, convulsions and death in a few dogs (Chen et al., 1938). Oral LD of niacinamide is 4.5-7 g/kg of body
50
weight in rats (NRC, 1987).

DRUG Validated interactions studies do not exist for niacinamide preparations. However,
INTERACTIONS niacinamide inhibits metabolism of primidone in mice and metabolism of primidone and
carbamazepine in humans. This probably occurs by inhibition of cytochrome P-450 by
nicinamide (Bourgeois et al., 1982).

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