Ascorbic Acid

Acidum ascorbinicum

For medical students2 min readUpdated 2026-10-10

Acidum ascorbinicum is a water-soluble vitamin that regulates metabolic processes. It exhibits prominent antioxidant, redox, and vasoprotective (angioprotective) properties.

Pharmacological groupAgents regulating metabolic processes

FormulationsPowder; tablets 0.025–0.1 g; solutions 5% and 10% (1–2 mL)

pKa constant11.5 (very weak acid)

Synergism with ironReduces Fe3+ to Fe2+ for improved intestinal absorption

Mechanism of Action and Physicochemical Properties

As a weak acid with an ionization constant $pK_a = 11.5$, ascorbic acid exists almost entirely in its un-ionized, lipophilic form within the body's physiological pH range (1–8). This property ensures its facilitated absorption in the gastrointestinal tract.

As a potent antioxidant, the drug participates in key oxidation-reduction (redox) processes. A classic clinical example of synergism is its combination with iron salts: vitamin C reduces ferric iron ($Fe^{3+}$) to the ferrous form ($Fe^{2+}$), which is absorbed much more efficiently by the body.

Pharmacological Effects

Key biological effects of the drug include:

Angioprotective action: strengthening the vascular wall and reducing capillary permeability.
Antioxidant defense: neutralizing free radicals and participating in redox reactions.
Immunomodulation: stimulating endogenous interferon production and enhancing leukocyte phagocytic activity, thereby increasing non-specific resistance to infections.
Antiscorbutic effect: specific prevention and treatment of avitaminosis C (scurvy).
Stimulation of regeneration: accelerating the healing of wounds, trophic ulcers, and bone fracture consolidation.

Clinical Indications

Vitamin C supplementation is indicated as part of combination pharmacotherapy for various pathological conditions:

Deficiency states: prevention and treatment of hypovitaminosis and avitaminosis (scurvy).
Infectious diseases to enhance host resistance.
Somatic disorders affecting the cardiovascular system, liver, lungs, and hematopoietic abnormalities.
Critical states: shock, circulatory collapse, and various types of poisoning.
Conditions of increased physical and psychological stress.

Adverse Effects and Safety

The drug is generally well tolerated at therapeutic doses; however, prolonged, uncontrolled use of high doses may cause adverse reactions. These include functional disorders of the urinary system (kidneys) and the pancreas.

Administration and Dosage

Both enteral and parenteral routes of administration are used in clinical practice:

Oral administration in doses from 0.05 to 0.1 g.
Parenteral administration (intramuscular or intravenous) using solutions in doses from 0.05 to 0.15 g.

Prescription writing utilizes powders, tablets of various dosages, or ampoule solutions.

Mnemonic

Ascorbic acid is a lone-ranger acid with a huge pKa (11.5): inside the body it stays 'armored' (un-ionized), absorbs easily, and shields blood vessels like a knight.

Frequently asked questions

In which specific biochemical reactions in the body does ascorbic acid act as a cofactor?

Ascorbic acid is a cofactor for the hydroxylation of proline and lysine residues during collagen synthesis. It is also involved in the following hydroxylation and synthetic pathways:

Serotonin biosynthesis: hydroxylation of tryptophan to 5-hydroxytryptophan;
Norepinephrine biosynthesis: hydroxylation of dopamine;
Tyrosine metabolism: hydroxylation of p-hydroxyphenylpyruvate to homogentisic acid;
Adrenal steroid hormone biosynthesis: hydroxylation of steroids from cholesterol;
Carnitine biosynthesis: hydroxylation of β-butyrobetaine;
Folate metabolism: conversion of folic acid into coenzyme forms, including tetrahydrofolic acid.

Ascorbic acid also participates in prothrombin synthesis.

What specific kidney and pancreatic complications are caused by prolonged high-dose vitamin C intake?

Prolonged high-dose intake of ascorbic acid causes general functional disturbances of the pancreas and kidneys. A specific complication affecting the urinary system is crystalluria. It occurs because vitamin C acidifies the urine (decreases pH), causing drug crystals to precipitate in the urinary sediment. Specific nosological forms of pancreatic injury are not detailed in the sources.

With which drug classes, besides iron salts, does ascorbic acid undergo clinically significant pharmacokinetic interactions?

In addition to iron preparations, ascorbic acid interacts pharmacokinetically with the following drug classes:

Sulfonamides — vitamin C acidifies the urine (decreases pH), increasing the risk of crystalluria (precipitation of drug crystals in the urine).
Bioflavonoids (Vitamin P) (Rutosidum) — rutoside facilitates the cellular uptake of ascorbic acid by converting it into monodehydroascorbic acid.

Why is ascorbic acid easily absorbed in the gastrointestinal tract?

Due to its high pKa value (11.5), the drug remains in an un-ionized, lipophilic form within the physiological pH of the GI tract, facilitating transmembrane passage.

What role does vitamin C play when co-administered with iron preparations?

Ascorbic acid acts as a reducing agent: it converts poorly absorbed ferric iron (Fe3+) into ferrous iron (Fe2+), thereby increasing its bioavailability.

What are the main manifestations of the drug's immunomodulating effect?

It stimulates interferon synthesis and increases the phagocytic activity of blood cells, thereby enhancing overall non-specific resistance to infections.

Go deeper

Impact of pH and pKa on the pharmacokinetics of weak acids
Mechanisms of synergism between vitamin C and ferrous iron
The role of redox systems in cellular antioxidant defense
Parenteral routes of administration for vitamin formulations
Pharmacodynamics of non-specific immunity stimulation