Vitamin PP: Pharmacokinetics and Biochemistry
Preparations of this group are absorbed from the intestinal lumen into the systemic circulation unchanged. Upon reaching the liver, the molecules are actively incorporated into biochemical processes, acting as a substrate for the synthesis of essential coenzymes. These include NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate), which ensure key oxidation-reduction reactions in tissues.
Vitamin PP is widely distributed in nature. Plant sources include whole-grain bread, mushrooms, nuts, vegetables (tomatoes, peppers), and legumes (soybeans, peas, beans). Animal sources include meat, fish, and offal (heart, kidneys, liver).
Pharmacodynamics: Nicotinic Acid vs. Nicotinamide
The group includes two main substances: nicotinamide and nicotinic acid (known under the trade name niacin). Both forms possess potent antipellagric action, but their pharmacological profiles differ significantly.
Only nicotinic acid is capable of producing the following specific effects:
- Vascular action: causes marked vasodilation and increases vascular wall permeability.
- Effect on hemostasis: stimulates the fibrinolytic activity of blood.
- Antiatherogenic action: when administered in high doses (3–4 g per day), it acts as a hypolipidemic agent. It inhibits the synthesis of very-low-density lipoproteins (VLDL), reduces the concentration of triglycerides and low-density lipoproteins (LDL), while simultaneously increasing the level of antiatherogenic high-density lipoproteins (HDL).
It is important to remember that nicotinamide is completely devoid of both vasodilating and hypolipidemic properties.
Clinical Application of Vitamin PP Preparations
The main indication for prescribing both forms is the prevention of hypovitaminosis and the treatment of pellagra.
In gastroenterology and hepatology, these drugs are used for liver diseases (cirrhosis, hepatitis) and gastritis accompanied by reduced acidity. They also stimulate tissue regeneration in slow-healing ulcers and wounds.
Specific indications for nicotinic acid include the combination therapy of ischemic cerebrovascular disorders, atherosclerosis, and vascular spasms of the extremities. For long-term therapy, a sustained-release form of nicotinic acid has been developed — Enduracin tablets.
Vitamin P (Bioflavonoids): Properties and Sources
The bioflavonoid group includes rutoside (rutin), dihydroquercetin (quercetin), hesperidin, and other compounds. Unlike vitamin PP, they are of exclusively plant origin. They are abundant in citrus fruits, black currants, rose hips, rowan berries, green tea, and nuts. Bioflavonoids are not found in animal products.
The main pharmacological effect of vitamin P is angioprotective. The drugs regulate vascular wall permeability, reduce capillary fragility, and exert a hypotensive effect. In addition, they exhibit antioxidant activity and possess choleretic properties.
Bioflavonoids interact closely with vitamin C. They convert ascorbic acid into monodehydroascorbic acid, which facilitates its penetration into cells. The action of combined preparations, such as Ascorutin (a combination of rutoside and ascorbic acid), is based on this mechanism.
Indications for Bioflavonoids
Vitamin P preparations are used for the prevention and treatment of specific deficiency states (hypo- and avitaminosis P).
In angiology, they are indicated for vascular pathology: increased capillary permeability and venous insufficiency, including thrombophlebitis.
In traumatology, bioflavonoids effectively combat edema of various origins and are used in the treatment of mechanical injuries and frostbite.
Briefly: answers to topical questions
What is the mechanism of the hypolipidemic action of nicotinic acid?
The mechanism of the hypolipidemic action of nicotinic acid consists of the inhibition of the enzyme triglyceride lipase in adipose tissue.
The cascade of reactions includes:
- Reduction of lipolysis in adipocytes and decrease in the formation of free fatty acids (FFAs).
- Decrease in FFA mobilization and their uptake by the liver.
- Decrease in the biosynthesis of triglycerides (TGs) in the liver.
- Reduction in the formation of very-low-density lipoproteins (VLDL) as a consequence of reduced TGs.
As a result, the levels of VLDL, IDL, and LDL decrease, while the level of antiatherogenic HDL increases.
What side effects are caused by the intake of nicotinic acid?
The intake of nicotinic acid causes side effects associated with vasodilation, allergic reactions, and toxic effects on the liver.
The main adverse manifestations include:
- Flushing (hyperemia) of the skin of the face, neck, and upper chest.
- Sensation of warmth and skin pruritus (due to the drug stimulating increased synthesis of prostaglandin D2).
- Gastrointestinal disorders.
- Cardiovascular disorders.
- Allergic reactions.
- Hepatotoxicity (liver dysfunction upon prolonged intake of high doses due to an excessive increase in NAD and NADP content).
Which drugs belong to the bioflavonoid group (vitamin P)?
The bioflavonoid group (vitamin P) includes rutin, quercetin, hesperidin, and their dosage forms.
Sources highlight the following drugs and active substances:
- Rutoside — for example, rutin.
- Dihydroquercetin — for example, quercetin.
- Hesperidin.
- Combined preparations — a combination of rutoside with ascorbic acid, for example, ascorutin.
The classic triad of pellagra symptoms (vitamin PP deficiency) is easily remembered as the "Rule of Three Ds": Diarrhea, Dermatitis, Dementia.
Class and exam questions
What is the difference between nicotinic acid and nicotinamide?
Both forms treat pellagra, but only nicotinic acid dilates blood vessels and lowers blood levels of atherogenic lipids. Nicotinamide does not possess these properties.
How does vitamin P interact with ascorbic acid?
It converts vitamin C into monodehydroascorbic acid. This is necessary for ascorbic acid to be able to cross the cell membrane into the cell.
Can vitamin P be obtained from animal-derived foods?
No, bioflavonoids are synthesized only by plants. They are completely absent in meat, fish, or offal.
What else to study on this topic
- The biochemical role of NAD and NADP in oxidation-reduction processes.
- The mechanism of inhibition of VLDL synthesis by nicotinic acid.
- Effect of nicotinic acid on blood fibrinolytic activity.
- Pharmacokinetics of sustained-release forms of nicotinic acid (Enduracin).
- Antioxidant properties of bioflavonoids at the cellular level.
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