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Nicotinic Acid

*Acidum nicotinicum*

For medical students2 min readUpdated 2026-10-10

Nicotinic acid (niacin) is a well-known vitamin supplement that, in high doses, acts as a potent lipid-lowering drug. Its primary clinical value lies in its ability to inhibit intracellular lipolysis in adipose tissue, leading to the normalization of the blood lipid profile.

Target of actionTAG lipase in adipocytes (fat cells)
Peak effectDevelops gradually — after 2 months of continuous therapy
DosageLipid-lowering dose (1.5–3 g) is hundreds of times higher than the vitamin dose (16 mg)
Side effectFlushing and warmth due to prostaglandin D2 release

Mechanism of Action and Effect on Lipids

The primary site of action for nicotinic acid is adipose tissue, specifically adipocytes. Normally, the enzyme TAG lipase (triacylglycerol lipase) breaks down triglycerides, releasing fatty acids into the bloodstream for delivery to the liver. Niacin inhibits this enzyme, triggering the following cascade of reactions:

  1. Lipolysis in adipocytes is reduced.
  2. The production of free fatty acids (FFAs) and their transport to the liver decrease.
  3. A substrate deficiency occurs in the liver, dropping triglyceride (TG) biosynthesis.
  4. Consequently, the production and secretion of atherogenic very-low-density lipoproteins (VLDLs) decline.

As a result of this therapy, the blood lipid profile changes dramatically. The drug lowers levels of VLDL, intermediate-density lipoproteins (IDLs), and low-density lipoproteins (LDLs). Conversely, the level of anti-atherogenic high-density lipoproteins (HDLs) increases.

Pharmacokinetics and Clinical Application

The drug is rapidly and completely absorbed from the gastrointestinal tract, with a bioavailability of approximately 72%. Metabolism occurs in the liver, and elimination is renal (primarily as metabolites). The half-life is very short, at just 45 minutes. Extended-release formulations are also available (e.g., enduracin).

Despite rapid pharmacokinetics, the maximum lipid-lowering effect develops slowly—requiring about two months of continuous therapy. After discontinuing the drug, the beneficial residual effect persists for 2 to 6 weeks.

Clinically, niacin is used for hyperlipoproteinemias types IIa, IIb, III, IV, and V. Highest efficacy is observed in types III and V. It is important to appreciate the massive difference in dosages: while the daily vitamin requirement is only about 16 mg, the therapeutic lipid-lowering dose reaches 1.5–3 g per day (hundreds of times higher).

Side Effects and Combination Therapy

The main issue with high-dose therapy is prominent adverse reactions: flushing (redness) of the face, neck, and upper chest, pruritus (itching), as well as gastrointestinal and cardiovascular disturbances.

These symptoms occur because nicotinic acid stimulates the enhanced synthesis of prostaglandins (specifically D2 and E2). Prostaglandin D2 activates DP1 receptors in cutaneous blood vessels, causing them to dilate. Note: this process is entirely unrelated to the lipid-lowering mechanism—there is no causal relationship between lipid reduction and prostaglandin release.

Two approaches are used to prevent "flushing":

Laropiprant is a selective DP1 receptor antagonist. It is rapidly absorbed (bioavailability 71%), metabolized via glucuronidation, and excreted through the intestines as a glucuronide. The half-life is approximately 17 hours. In modern practice, combination products (such as Tredaptive) containing 1000 mg of nicotinic acid and 20 mg of laropiprant are used. This allows for high therapeutic doses of niacin with a minimal risk of cutaneous reactions.

Mnemonic

To remember the niacin cascade, use the rule of "Three Ds" (adapted from the Russian three C's): Decreased lipolysis in adipose tissue → Decreased hepatic triglyceride synthesis → Decreased VLDL in the blood.

Frequently asked questions

What systemic side effects (aside from skin reactions) are caused by high doses of nicotinic acid?

High doses of nicotinic acid cause systemic side effects including gastrointestinal and cardiovascular disturbances. Systemic manifestations also include marked vasodilation both peripherally and in the brain. These adverse events accompany the characteristic cutaneous reactions (flushing of the face, neck, upper chest, and itching) that develop due to the stimulation of prostaglandin synthesis.

Why does nicotinic acid cause facial flushing and itching?

The drug stimulates the synthesis of prostaglandin D2, which activates specific receptors in skin blood vessels, causing profound vasodilation and increased blood flow.

Is the release of prostaglandins related to the lipid-lowering effect?

No, these are two parallel processes. The reduction in lipid levels and the synthesis of prostaglandins have no causal relationship.

How can skin reactions be prevented when taking niacin?

It is recommended to take acetylsalicylic acid 30 minutes before niacin or use combination products containing receptor blockers (e.g., laropiprant).

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