What white rectangular shaped pill and has 5312 on one side and 500 on the other?

NIACIN Slo-Niacin Extended Release Tablets NIACIN, also known as Nicotinic Acid or Vitamin B3, (Niacor®, Nicolar®) is a B-vitamin that occurs naturally in foods, such as meat, fish, milk, eggs, green vegetables, and enriched cereal grains. Proper amounts of niacin are obtained in our diets daily. Niacin supplements are occasionally prescribed to treat pellagra, a serious but rare niacin-deficiency disorder. Niacin is available in many multivitamins in small amounts.