Background And Relevant Pharmacokinetics

Vitamin B3 (niacin) is a water-soluble vitamin of the B complex family. Both nicotinic acid and nicotinamide are absorbed in the stomach and small intestine by passive diffusion at high doses, or sodium-dependent facilitated diffusion at low doses, and excreted in the urine. Recent studies suggest that regulation of niacin uptake may be regulated by an acidic pH-dependent carrier-mediated system and PTK-mediated pathway (Nabokina et al 2005). The immediate-release form of nicotinic acid reaches peak concentration at 45 minutes and the extended release form in 4-5 hours. While nicotinamide can be directly converted to nicotinic acid, nicotinic acid must undergo a number of metabolic steps to produce NAD(+) before being converted to nicotinamide (Hendler & Rorvik 2001, Wilson et al 1991). The body's niacin requirement is also met by the biosynthesis of niacin from tryptophan, an amino acid It has been estimated that each 60 mg excess of tryptophan (after protein synthesis) is converted to approximately 1 mg of niacin. In the absence of sufficient levels of B3 the body will preferentially convert tryptophan to B3. Niacin is widely distributed throughout the body and concentrates in the liver, spleen and adipose tissue. It is finally excreted by the kidneys. COMMON FORMS AVAILABLE

The term niacin is used to refer to both nicotinic acid (niacin) and nicotinamide (niacinamide). Niacin is also referred to as vitamin B3.

The immediate-release form, which requires more regular dosing, is associated with significant vasodilation ('flushing'), whereas the sustained-release form is associated with an increased risk of adverse events. Extended-release forms of niacin Vitamin B3 — Niacin 1222

allow once-daily dosing and avoid much of the flushing and hepatotoxicity of the immediate- and sustained-release preparations (Sadovsky 2002).

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