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PHARMACOLOGICAL ACTIVITIES - TOXICOLOGY - DRUG INTERACTIONS

Pyridoxine Hydrochloride [Vitamin B ] (C H NO ·HCl)
6 8 11 3

The liver is the primary organ for metabolism of vitamin B , and it releases the active form
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pyridoxal-5-phosphate (PLP) into the circulation to supply other tissues. Low riboflavin status
leads to a reduction in circulating PLP (NRC, 2006). PLP plays a vital role in the function of
approximately 100 enzymes that catalyze essential chemical reactions in the body. PLP
functions as a coenzyme for glycogen phosphorylase, an enzyme that catalyzes the release of
glucose from stored glycogen. Much of the PLP in the body is found in muscle bound to glycogen
phosphorylase. PLP is also a coenzyme for reactions used to generate glucose from amino
acids, a process known as gluconeogenesis (Shils et al., 2006).

Vitamin B deficiency can result in growth depression, a mild microcytic hypochromic anemia
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with elevated serum iron; convulsive seizures, and irreversible kidney lesions consisting
of tubular atrophy and dilation, fibrosis, and intratubular deposits of birefringent crystals
(NRC, 1986). It may also cause a dull, waxy, unkempt coat with fine scales and patchy alopecia
(Watson, 1998).

Toxicity for vitamin B has not been documented in dogs and cats when administered orally in therapeutic doses.
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However, studies have suggested that probably 1,000 times the nutritional requirements would have to be
TOXICOLOGY According to another report, dogs can tolerate up to 1 g of pyridoxine/kg of body weight for a short duration of
included in diets in order to produce signs of toxicity. The LD for vitamin B in dogs is 1 g/kg of body weight.
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time, but over longer periods can cause ataxia, muscle weakness and neurological damage (Friedrich, 1988). In
another study dogs administered 50 mg of pyridoxine hydrochloride/kg of body weight reported no signs of toxicity
(Phillips et al., 1978). Levels of pyridoxine of 1,000 mg/kg of diet for less than 60 days, or less than 500 mg/kg
of diet for more than 60 days, appear to be safe for dogs (NRC, 1987).

DRUG Pyridoxine deficiency can occur with medications such as isoniazid, cycloserine, and
INTERACTIONS penicillamine. High doses of pyridoxine may decrease the efficacy of phenobarbital and
phenytoin (Shils et al., 2006; Bender, 1999). Pyridoxine 10-25 mg may be enough to inhibit
levodopa (Leon et al., 1971).

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