Biorelevant In Vitro Release Testing and In Vivo Study of Extended-Release Niacin Hydrophilic Matrix Tablets

Area of Science:

• Pharmacokinetics
• Drug Delivery
• Formulation Science

Background:

• Niacin (nicotinic acid) is an antihyperlipidemic agent administered in extended-release (ER) tablets.
• High doses of niacin ER exhibit variable plasma levels and potential side effects due to rapid absorption and extensive metabolism.
• Compendial in vitro release testing cannot adequately predict the in vivo performance of niacin ER formulations.

Purpose of the Study:

• To compare a newly developed ER HPMC niacin formulation with an originator product.
• To design a robust niacin matrix tablet with comparable biopharmaceutical behavior, safety, and efficacy.
• To investigate the in vitro and in vivo performance of niacin ER formulations under physiological conditions.

Main Methods:

• Developed and characterized a novel ER HPMC niacin formulation.
• Conducted extensive in vitro investigations, including dynamic studies in flow-through cell apparatus and a stress test device.
• Evaluated nicotinic acid plasma concentrations in vivo after administration of both marketed and test products.

Main Results:

• Erratic, multiple nicotinic acid plasma peaks were observed with both extended-release products.
• This behavior is attributed to local input exceeding the metabolic threshold due to mechanical stresses, not solely formulation.
• The study demonstrated similar in vivo performance for the test and originator products despite formulation differences.

Conclusions:

• Robust formulation design alone does not guarantee bioequivalence for niacin ER products.
• The intrinsic pharmacokinetic characteristics of nicotinic acid, specifically its highly variable and extensive metabolism, are the primary drivers of erratic plasma levels.
• In vitro dissolution tests are insufficient to predict the in vivo behavior of niacin ER due to complex physiological factors.