niacin (vitamin B₃, nicotinic acid)
Niacor, Niaspan, Nico-400, Nicotinex, Slo-Niacin

niacinamide (nicotinamide)

Available forms
Available by prescription only
Tablets: 500 mg
Tablets (extended-release): 500 mg, 750 mg, 1,000 mg
Available without a prescription
Capsules (extended-release): 125 mg, 250 mg, 400 mg, 500 mg
Elixir: 50 mg/5 ml
Tablets: 50 mg, 100 mg, 250 mg, 500 mg
Tablets (extended-release): 250 mg, 500 mg, 750 mg

Indications and dosages
 Pellagra. Adults: 300 to 500 mg in divided doses P.O. daily, depending on severity of niacin deficiency.
Children: 100 to 300 mg P.O. daily in divided doses, depending on severity of niacin deficiency.
 Peripheral vascular disease and circulatory disorders. Adults: 100 to 150 mg P.O. three to five times daily. Or, 300 to 400 mg (extended-release preparation) P.O. q 12 hours.
 Adjunctive treatment of hyperlipidemias, especially those related to hypercholesterolemia. Adults: 1 to 6 g P.O. daily in two to four divided doses with or after meals. Maximum, 6 g daily. Or, initial dose of 100 mg P.O. t.i.d., increasing by 300 mg daily at 4- to 7-day intervals. Or, 500 mg P.O. t.i.d. with gradual increase to desired effect. Or, 500 mg (extended-release preparation) P.O. h.s. Increase by 500 mg daily at 4-week intervals if needed. Maximum dose is 2 g daily. Usual dose is 1 to 2 g daily h.s.
 Hartnup disease. Adults: 50 to 200 mg P.O. daily in divided doses.

Pharmacodynamics
Vitamin replacement action: As a vitamin, niacin functions as a coenzyme essential to tissue respiration, lipid metabolism, and glycogenolysis. Niacin deficiency causes pellagra, which causes dermatitis, diarrhea, and dementia; administration of niacin cures pellagra. Niacin lowers cholesterol and triglyceride levels by an unknown mechanism.
Vasodilating action: Niacin acts directly on peripheral vessels, dilating cutaneous vessels and increasing blood flow, predominantly in the face, neck, and chest.
Antilipemic action: Mechanism of action is unknown. Nicotinic acid inhibits lipolysis in adipose tissues, decreases hepatic esterification of triglyceride, and increases lipoprotein lipase activity. It reduces serum cholesterol and triglyceride levels.

Pharmacokinetics
Absorption: Absorbed rapidly from the GI tract. Cholesterol and triglyceride levels decrease after several days.
Distribution: Coenzymes are distributed widely in body tissues; niacin appears in breast milk.
Metabolism: Metabolized by the liver to active metabolites.
Excretion: Excreted in urine.

Contraindications and precautions
Contraindicated in patients with hepatic dysfunction, active peptic ulcer, severe hypotension, arterial hemorrhage, or hypersensitivity to drug. Use cautiously in patients with history of liver disease, peptic ulcer, allergy, gout, gallbladder disease, diabetes mellitus, or coronary artery disease.

Interactions
Drug-drug. Aspirin: May decrease the metabolic clearance of nicotinic acid. Use together cautiously.
Sympathetic blocking agents: May cause added vasodilation and hypotension. Use together cautiously.

Adverse reactions
Most reactions are dose-dependent. CV: excessive peripheral vasodilation, hypotension, atrial fibrillation, arrhythmias, flushing.
EENT: toxic amblyopia.
GI: nausea, vomiting, diarrhea, possible activation of peptic ulceration, epigastric or substernal pain.
Hepatic: hepatic dysfunction.
Metabolic: hyperglycemia, hyperuricemia.
Skin: pruritus, dryness, tingling.

Effects on lab test results
• May increase glucose, AST, ALT, and uric acid levels.

Overdose and treatment
Niacin is a water-soluble vitamin and seldom causes toxicity in patients with normal renal function.

Special considerations
• The RDA of niacin is 16 mg in men, 14 mg in women, 18 mg in pregnant women, and 4 to 16 mg in infants and children.
• Megadoses of niacin usually aren’t recommended.
• Premedication with aspirin, use of the slow-release formulation, and gradual dose adjustments may reduce flushing response.
• Niacin therapy alters fluorometric test results for urine catecholamines and results for urine glucose tests using cupric sulfate (Benedict’s reagent).
Breast-feeding patients
• There have been no reports of problems in breast-feeding women taking normal daily doses as dietary requirement.

Patient education
• Explain disease process and rationale for therapy. Stress that use of niacin to treat hyperlipidemia or to dilate peripheral vessels isn’t simply taking a vitamin but taking a serious medicine. Emphasize the importance of complying with therapy.
• Instruct patient not to substitute extended-release for intermediate-release dosage forms in equivalent doses. Severe hepatotoxicity, including necrosis, has occurred.
• Explain that cutaneous flushing and warmth commonly occur in the first 2 hours and that this will cease with continued therapy.
• To minimize the effects of orthostatic hypotension, advise against making sudden postural changes.
• To reduce flushing response, instruct patient to avoid hot liquids early in therapy.
• Advise patient to take drug with meals to minimize GI irritation.
• To prevent recurrence of pellagra after symptoms subside, advise adequate nutrition and adequate supplements to meet RDAs.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use