Niacin, known as vitamin B3, is a water-soluble, vitamin of the B complex group of vitamins. Food such as bran, yeast, eggs, peanuts, poultry, red meat, fish, whole-grain cereals, legumes, and seeds are rich sources of the vitamin. As a drug, it has two main indications:
Indication for Pellagra
Pellagra is the deficiency of vitamin B3. Niacin is indicated in the treatment of pellagra until the symptoms resolve, most commonly for the relief of skin symptoms.
Indication for Dyslipidemia
Therapeutic doses of niacin can reduce the level of total cholesterol up to 25%, low-density lipoprotein (LDL) up to 10% to 15%, and triglycerides by up to 20% to 50%. Niacin has the highest efficacy to raise high-density cholesterol (HDL), with an increase of 15% to 35%. Its use is in moderate to high doses (1000 to 3000 mg per day) for refractory dyslipidemia and cases warranting HDL increase.
With more evaluation, niacin may be in a grouping with hypolipidemic drugs used for patients with:
Niacin is necessary for adequate cellular metabolism and function as a vital component in coenzyme 1 (the oxidized form of nicotinamide adenine dinucleotide [NAD]) and coenzyme 2 (the reduced form of nicotinamide adenine dinucleotide phosphate [NADP]), which either accept or donate hydrogen ions in essential oxidation-reduction reactions. They are important coenzymes for glycolysis, pyruvate metabolism, protein, and amino acid metabolism, pentose biosynthesis, glycerol metabolism, synthesis of high energy phosphate bonds, and fatty acid metabolism. As cellular functions in many organs and tissues are affected by the deficiency of niacin, the clinical expression of pellagra is diverse.
Mechanism of action of niacin in dyslipidemia includes inhibition of lipolysis within adipose tissue, reduction in liver triacylglycerol formation, increase in lipoprotein lipase activity, inhibition of synthesis of apo B-100 and hepatic very-low-density lipoprotein (VLDL), impaired cholesterol biosynthesis and lowering of the fractional catabolic rate of HDL-Apo A-1. Apo A-1, which is an activator of lecithin cholesterol acyltransferase (LCAT), has a significant role in reverse cholesterol transport.
Niacin decreases the risk of cardiovascular disease by exhibiting a plethora of pleiotropic effects, especially by its anti-oxidative and anti-inflammatory actions and by increasing serum adiponectin.
Recommended daily allowance of niacin is as follows:
The adult dose is nicotinamide 100 mg orally, every 6 hours for several days until relief of acute symptoms, followed by 50 mg every 8 to 12 hours until all skin lesions heal. In severe cases (marked neurological or gastrointestinal tract symptoms), 1 g three to four times a day can be given, initially by the parenteral route. For children, one can use 10 to 50 mg orally every 6 hours until symptoms of pellagra resolve. For mild endemic pellagra, smaller doses such as 10 mg per day are acceptable. Therapy should include other B vitamins, magnesium, and zinc as well as a calorie-rich diet. Topical emollients may reduce discomfort due to skin lesions. Sustained-release (SR) formulations have been developed which are available over-the-counter. Sustained-release niacin can be administered once daily and is less likely to cause flushing. However, it does not have approval for use in hyperlipidemia, and some studies showed a high likelihood of hepatotoxicity.
The recommended dose for hyperlipidemia is 1 to 6 g daily, initially low doses (100 mg three times per day), increasing at weekly intervals depending upon effect and tolerance. Extended-release (ER) niacin in concentrations from 125 to 1000 mg is approved for use in hyperlipidemia and does not have hepatotoxicity compared to regular niacin.
Niacin causes vasodilation of small subcutaneous blood vessels mediated by prostaglandin D2 that leads to a cutaneous flush, accompanied by an uneasy sensation of pruritus and warmth. Severe flushing may lead to hypotension and dizziness. Flushing appears earlier after dosing with immediate-release (IR) niacin (approximately 30 minutes) and delayed for sustained-release niacin (2 to 4 hours). Patients should avoid hot showers immediately after a dose, and if necessary, aspirin or ibuprofen is helpful.
Peptic Ulcer Disease
Niacin therapy may aggravate peptic ulcer disease. Niacin should be used cautiously with active or chronic gastrointestinal disorders.
The most serious adverse effect is niacin hepatotoxicity. A mild increase in hepatic transaminase levels up to twice the upper limit of the normal range is common.
Decreased glucose tolerance and hyperglycemia can occur in individuals with diabetes and is thought to result from insulin resistance consequent to the free fatty acid rebound after moderately-sized doses.
Patients with supraventricular tachycardias (SVTs) may experience unusual chest sensations and palpitations even when the SVTs are under control via concomitant antiarrhythmic therapy.
Reports also exist of retinal edema or toxic amblyopia resulting in blurred vision.
Vitamin B3 underdosing in vulnerable population groups may result in pellagra, which is characterized by 4 Ds in clinical manifestations: diarrhea, dermatitis, dementia, and death.
Dermatitis: The diagnosis is challenging in the absence of the skin lesions and is more straightforward if characteristic skin lesions are present. Dermatitis begins as erythema, resembles sunburn in the initial stages, but tanning occurs more slowly than typically seen in sunburn. The lesion is a bilaterally symmetrical eruption located at sites of sunlight exposure. Cutaneous patches on the neck are known as Casal necklace. It extends as a broad collar around the cervical dermatomes C3 and C4 in the neck.
Diarrhea: Gastrointestinal disturbances include diarrhea, nausea, vomiting, epigastric discomfort, poor appetite, abdominal pain, and increased salivation. Stools are typically watery but can be bloody or mucoid occasionally.
Neurologic manifestation: Presents as nonspecific symptoms like confusion, hallucinations, irritability, psychomotor unrest, ataxia, and depression. As the disease advances, patients become confused, disoriented, and delirious, then comatose and stuporous, and finally die.
Contraindications to the use of niacin are as follows:
Niacin Therapy for Pellagra
A combined excretion of pyridone and N-methyl nicotinamide of less than 1.5 mg in 24 hours points toward severe niacin deficiency.
Niacin therapy for Dyslipidemia
Recommendations include monitoring of uric acid, blood glucose, and potassium.
Maximum Tolerated Dose of Niacin
Immediate-Release formulation: 6 g/day in 2 to 3 divided doses
Sustained-Release formulation: 2000 mg per day
Symptoms of toxicity include nausea, vomiting, diarrhea, flushing, dizziness, and palpitations. Treatment of toxicity involves supportive care, including gastric lavage.
Healthcare workers, including nurse practitioners and the primary care provider, should not empirically encourage patients to take niacin. It is only recommended if there is a deficiency. For the management of hyperlipidemia, the vitamin often causes intolerable side effects, and its use is declining. The majority of the public should be encouraged to eat fresh fruit and veggies to obtain their niacin. Reliance on supplements is not recommended because of fake and counterfeit products.
When using niacin, an interprofessional approach is useful, especially depending on why it is necessary. The clinician will initiate therapy; if for pellagra or deficiency, a nurse, pharmacist, and dietician should all work together to resolve the condition. For dyslipidemia, a cardiologist may also be necessary. Pharmacists will verify the dosing based on the condition and can offer counsel to the patients, as can the nurse. For example, it is sometimes recommended to take a baby aspirin before dosing niacin to help prevent the flushing. Of course, this would be with once-daily dosing. The nurse should counsel the patient on what to expect with niacin therapy, and monitor for adverse effects as well as patient compliance and treatment effectiveness. The dietician can review the patient's eating habits to determine where the possible deficiency lies. All these ancillary providers need to keep the treating clinician informed at all times. Thus, with an interprofessional collaborative approach, niacin therapy can deliver optimal therapeutic results with minimal adverse effects to the patient. [Level V]
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