Effect of the Rate of Niacin Administration on the Plasma and Urine Pharmacokinetics of Niacin and Its Metabolites

The pharmacokinetics, efficacy, and safety of niacin and its various formulations are discussed. Niacin has been used for decades for the treatment of dyslipidemia because of its favorable effects on all lipoprotein parameters. Niacin significantly increases high-density lipoprotein cholesterol (HDL-C) more than any other available agent and reduces total cholesterol, low-density lipoprotein cholesterol (LDL-C), lipoprotein (a), and triglycerides. Niacin is currently available in immediate-release (IR), sustained-release (SR), and extended-release (ER) formulations that differ in their dissolution, pharmacokinetic, efficacy, and safety profiles. Important drawbacks to niacin therapy such as cutaneous flushing, associated with IR niacin, and hepatotoxicity, associated with SR niacin, have historically limited its use. The adverse effect profiles of the different niacin formulations can be explained by differences in their dissolution and absorption rates and metabolic disposition, which result in production of metabolites associated with the respective adverse effects. The ER niacin formulation, with an intermediate dissolution rate between the dissolution rates of IR and SR niacin, demonstrates reduced rates of cutaneous flushing compared with IR niacin and hepatotoxic effects compared with SR niacin. Pharmacists need to be familiar with the pharmacokinetics, efficacy, and safety of available niacin formulations so that they can optimally educate both patients and health care providers on the differences among niacin formulations, counsel on the proper selection of a niacin product, and provide strategies for improving tolerance and adherence to therapy.

Immediate-release niacin manifests beneficial effects in cardiovascular disease with respect to dyslipidemic states. It lowers low-density lipoprotein (LDL) cholesterol, triglycerides, lipoprotein(a), and apoprotein B; at the same time, it increases high-density lipoprotein (HDL) cholesterol, HDL2, and apoprotein A-I. However, use of crystalline niacin has drawbacks: therapy requires multidose regimens, and side effects include flushing and pruritus. Slowing absorption with sustained-release formulations succeeds in decreasing flushing and increasing tolerance, but increases in hepatic enzyme levels have raised safety concerns. A new extended-release, once-daily formulation of niacin (Niaspan) shows promise in minimizing flushing while avoiding hepatotoxicity. A multicenter, randomized, double-blind clinical trial of Niaspan enrolled 122 patients with confirmed diagnosis of primary dyslipidemia (LDL cholesterol >4.14 mmol/L [160 mg/dL] and triglycerides <9 mmol/L [800 mg/dL]) into 3 treatment groups: (1) Niaspan 1,000 mg/day; (2) Niaspan 2,000 mg/day; and (3) placebo. The primary treatment endpoint was LDL-cholesterol level. This endpoint was not significantly affected by placebo (0.2% increase), but Niaspan decreased LDL cholesterol by 5.8% (1,000 mg/day) and 14.6% (2,000 mg/day) (p <0.001). Likewise, with placebo there were significant changes in total cholesterol, triglycerides, lipoprotein(a), and apoprotein B, whereas both Niaspan 1,000 and 2,000 mg/day significantly (p <0.001) decreased these parameters. In addition, both Niaspan groups showed significant (p <0.001) increases in HDL cholesterol (17% and 23%, respectively), including HDL subfractions. With respect to flushing, 20% of the placebo group reported at least 1 episode, whereas 88% and 83% of the Niaspon 1,000- and 2,000-mg/day groups, respectively, reported episodes. There was no hepatotoxicity as liver enzyme levels remained within clinically accepted limits in all treatment groups. However, Niaspan 2,000 mg/day showed a significant increase in aspartate aminotransferase compared with baseline and placebo. This trial demonstrated a cholesterol-modifying effect of Niaspan consistent with those reported for niacin, but demonstrated a better tolerance for flushing. Moreover, in contrast to sustained-release formulations, Niaspan showed relatively mild hepatic effects.

Niacin (nicotinic acid) is the broad-spectrum lipid drug, which lowers the concentration of all atherogenic plasma lipids/lipoproteins and at the same time raises the levels of the protective HDL (high-density lipoprotein). Niaspan is a prolonged release (PR) formulation of niacin, which has considerable advantages over both immediate release (IR) and slow release (SR) formulations of this drug. The major early side effect of IR niacin, the flush, is reduced with Niaspan. The hepatotoxic effects with SR niacin are not present with Niaspan. It is suitable for once daily prescription at bedtime. Niaspan is effective as monotherapy and in combination with other lipid-lowering drugs such as statins and fibrates. It is particularly useful for treatment of the dyslipidaemia of type 2 diabetes, where IR but not PR niacin may deteriorate the diabetic condition. Overall, niacin, now available as the well-tolerable drug formulation Niaspan, is the unique broad-spectrum lipid drug for the prevention and treatment of clinical atherosclerosis.