What is niacin, and how does it work (mechanism of action)?
Niacin (nicotinic acid, vitamin B3) is a part of
the normal diet that is essential to various chemical reactions in the body. It
is used medically to treat individuals with deficiency of niacin. Advanced
deficiency of niacin can lead to a condition called pellagra in which
individuals develop diarrhea,
dermatitis (inflammation of the skin), and
dementia. Niacin also is used to reduce cholesterol and
triglyceride levels in
the blood. Specifically it reduces bad cholesterol (LDL cholesterol) and
increases good cholesterol (HDL cholesterol). It is not clear how niacin causes
its effects on cholesterol and triglyceride levels, but it may be by reducing
the production of proteins that transport cholesterol and triglycerides in the
blood.
Niacin is available in immediate and slow-release forms (Niaspan,
Slo-Niacin). Natural sources of niacin include meat, poultry, liver, fish, nuts,
green vegetables, whole grains, and potatoes. Niaspan was approved by the FDA in
July 1997.
What brand names are available for niacin?
Niacor, Niaspan, Slo-Niacin, Nicolar (discontinued)
Is niacin available as a generic drug?
Yes
Do I need a prescription for niacin?
Most formulations are available over the counter.
What are the side effects of niacin?
The most common side effects of niacin are:
- stomach upset,
- flushing,
- headache,
- reduced blood pressure upon standing (orthostatic hypotension),
- vomiting,
- diarrhea,
- itching and
- tingling sensations of the extremities.
Flushing may be reduced by taking 325 mg of aspirin 30 minutes
before the niacin and by increasing the dose of niacin slowly. Drinking hot
liquids or alcohol shortly before or after niacin is taken may increase the
occurrence of flushing. Extended release formulations of niacin may cause
flushing less frequently than immediate release formulations.
Rare cases of liver failure or muscle injury have occurred from the use of niacin. Blood tests
to monitor for liver injury should be performed before niacin therapy begins,
every 6-12 weeks for the first year, and then occasionally thereafter. Niacin
should be discontinued if liver tests are greater than three times the upper
limit of normal, are persistently elevated, or are accompanied by nausea,
vomiting, or weakness.
What is the dosage for niacin?
The recommended oral dose of immediate release niacin for treating
high cholesterol levels in adults is 1-2 g two to three times daily. The maximum
recommended dose is 6 g daily. When using extended release tablets, the maximum
recommended dose is 2 g per day. Niacin should be started at low doses and
increased slowly over several weeks. To avoid stomach upset, niacin should be
taken with meals.
Extended release tablets should be swallowed whole and should not be crushed
or chewed. Extended release formulations should not be substituted with
equivalent doses of immediate release niacin since this leads to an overdose of
niacin that may cause liver failure.
Pellagra may be treated with up to 500 mg per day of oral niacin.
Which drugs or supplements interact with niacin?
Use of niacin with drugs that cause liver or muscle
injury, for example, lovastatin (Mevacor) or simvastatin (Zocor) may increase
the occurrence of liver or muscle injury.
Niacin may increase blood glucose levels in individuals with
diabetes. Therefore, medications
for controlling blood glucose may need to be adjusted when niacin is taken by
those with diabetes.
Bile acid sequestrants (for example, cholestyramine
[Questran]) bind and
prevent absorption of niacin. Administration of bile acid sequestrants and
niacin should be separated by 4-6 hours.
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Is niacin safe to take if I’m pregnant or breastfeeding?
It is not known whether the high doses of niacin used in treating
elevated cholesterol levels are harmful to the fetus during
pregnancy.
Niacin is actively secreted in
breast milk. Therefore,
nursing mothers taking niacin should avoid breastfeeding or discontinue niacin
in order to prevent the newborn from ingesting large amounts of niacin.
What else should I know about niacin?
What preparations of niacin are available?
Tablets: 250, 500, 750, and 1000 mg. Capsules: 250 and 500 mg
How should I keep niacin stored?
Niacin should be stored at room temperature from 15 C to 30 C
(59 F to 86 F).