Ascorbic Acid

Introduction Overview

Generic Name

ascorbic acid

Brand Name

Acerola, Ascorbic Acid Quick Melts, Cemill 1000, C-Time, Easy-C, Ester-C, N Ice with Vitamin C, Vasoflex HD, Vicks Vitamin C Drops, Vitamin C, Vitamin C TR, Vitamin C with Rose Hips, C/Rose Hips, Cecon, Cemill 500, Sunkist Vitamin C, Cenolate, Mega-C-Acid Plus, Cee-500, C-500-Gr, Centrum Singles-Vitamin C, Ascot, Cevi-Bid, Time Release Vitamin C, Ascor L NC, Ascor, Bio C 1:1, Immune Essentials, Vitafusion Power C Gummies, Xcellent C, Alive Vitamin C, Ester-C 24hour Immune Support

Dosage Form

oral capsule (1000 mg with rose hips; 333.33 mg; 500 mg; 750 mg; with bioflavonoids 500 mg; with citrus bioflavonoids 1000 mg; with citrus bioflavonoids 500 mg), oral capsule extended release (500 mg), oral liquid (500 mg/5 mL), oral powder for reconstitution (500 mg/4 g), oral tablet (1000 mg; 1500 mg; 250 mg; 500 mg; with bioflavonoids; with bioflavonoids 500 mg; with citrus bioflavonoids 1000 mg; with citrus bioflavonoids 500 mg), oral tablet chewable (120 mg; 125 mg; 250 mg; 500 mg; 60 mg), oral tablet disintegrating (100 mg; 250 mg)

Drug Class

Vitamins

Pharmacokinetics

Absorption

Ascorbic acid (vitamin C) is rapidly and almost completely absorbed from the small intestine via active transport and passive diffusion mechanisms. Absorption efficiency decreases with increasing doses, with near-complete absorption at low doses (around 70-90% at doses of 30-180 mg) but only about 50% absorption at mega doses (>1 gram). Factors affecting absorption include the presence of food, gastrointestinal transit time, and gastrointestinal pH. Its bioavailability is optimal when administered orally in standard doses. Intramuscular and intravenous administration bypass gastrointestinal absorption, providing direct systemic availability beneficial in certain clinical situations such as severe deficiency.

Clinical studies indicate that oral absorption saturates at high doses, leading to renal excretion of excess amounts. This characteristic is critical in dosing for therapeutic applications, balancing efficacy with tolerability. Formulations such as extended-release capsules are employed to improve plasma vitamin C levels and reduce gastrointestinal side effects associated with high doses.

Distribution

After absorption, ascorbic acid is widely distributed in body tissues and fluids. It accumulates especially in metabolically active organs such as the adrenal glands, pituitary gland, brain, eyes, and white blood cells, reflecting its roles in collagen synthesis and antioxidant activity. Plasma concentrations are tightly controlled; normal plasma levels range between 50-70 µmol/L, but tissues maintain higher concentrations through active transport mechanisms involving sodium-dependent vitamin C transporters (SVCT1 and SVCT2).

Ascorbic acid crosses cellular membranes via specific transporters rather than passive diffusion, ensuring controlled intracellular levels. It does not extensively bind to plasma proteins. The volume of distribution approximates total body water, consistent with its hydrophilic nature. Its distribution dynamics are important for its biological roles and therapeutic effects.

Metabolism

Ascorbic acid undergoes limited metabolism in the human body. It is mainly oxidized to dehydroascorbic acid, which can be recycled intracellularly back to ascorbic acid or further metabolized into oxalic acid and other metabolites. The metabolic pathways involve enzymatic and nonenzymatic oxidation-reduction reactions that contribute to its antioxidant properties.

The liver plays a modest role in its metabolism. Because humans lack the enzyme L-gulonolactone oxidase necessary for endogenous vitamin C synthesis, they rely solely on dietary intake. The balance between oxidation and recycling determines the overall availability of active ascorbic acid in tissues. Variations in metabolism may occur in pathological states such as oxidative stress and inflammation, affecting dosing strategies.

Elimination

Ascorbic acid is eliminated primarily via renal excretion. The kidneys filter circulating vitamin C, with renal tubular reabsorption mediated by SVCT1 transporters, regulating plasma concentrations. Excess ascorbic acid beyond the renal threshold is excreted in urine, which serves as a safety mechanism preventing toxicity.

The elimination half-life varies with plasma concentration and follows nonlinear characteristics due to saturation of renal reabsorption at higher doses. At physiological levels, the half-life is approximately 10-20 days, but is much shorter at pharmacological doses due to increased clearance. Renal impairment may reduce elimination capacity leading to accumulation and increased risk of side effects. Hence, dose adjustment may be necessary in patients with renal dysfunction.

Dosage Forms

Adults

For dietary supplementation, adults typically require daily doses ranging from 50 mg to 200 mg, depending on individual nutritional status and health conditions. Therapeutic dosing for urinary acidification may range from 4 to 12 g per day divided into 3 to 4 doses, administered orally or by injection. In treating scurvy, doses between 100 to 250 mg once or twice daily for at least two weeks are recommended.

Administration routes include oral (tablet, capsule, liquid, powder), intramuscular, intravenous, and subcutaneous injections where indicated clinically. Extended-release capsules should be swallowed whole to maintain steady plasma levels. Chewable and disintegrating tablets must be taken as per instructions to ensure proper absorption.

Patients should follow healthcare provider dosing recommendations carefully, considering factors such as age, health status, and specific therapeutic goals.

Adolescents

Adolescents generally receive dosage ranges similar to adults for vitamin C supplementation, which are calibrated to age and weight. For dietary purposes, 35 to 100 mg per day is typical in pediatric and adolescent patients. For urinary acidification, doses may be 500 mg every 6 to 8 hours. In cases of scurvy, 100 to 300 mg per day divided into doses for at least two weeks is standard.

Formulations suitable for adolescents include chewable tablets, liquid preparations, and capsules, which may ease administration and adherence. Extended-release forms may be used cautiously with medical advice. Dosage adjustments are essential in adolescents with specific medical conditions or increased physiological needs such as growth spurts.

Special Populations

In patients with renal impairment or predisposition to kidney stones, cautious use or dose adjustments of ascorbic acid are advised due to the risk of oxalate nephropathy. High doses should be avoided or used under medical supervision.

During pregnancy and breastfeeding, adequate vitamin C intake is important, but excessive doses should be avoided. Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency require caution as high doses may increase the risk of hemolysis.

Elderly patients may require supplementation due to decreased dietary intake or altered metabolism. In surgical patients or those undergoing medical procedures, vitamin C status should be evaluated to optimize healing. Formulation choice should consider swallowing ability and tolerability.

Mechanism Of Action

Ascorbic acid (vitamin C) acts primarily as a vital antioxidant and enzymatic cofactor that participates in numerous physiological and biochemical processes. At the molecular level, it functions as a reducing agent, donating electrons to neutralize reactive oxygen species (ROS) and reactive nitrogen species, thereby mitigating oxidative stress and protecting cellular macromolecules such as DNA, proteins, and lipids from oxidative damage.

It serves as a cofactor for several critical enzyme systems, notably in the hydroxylation of proline and lysine residues during collagen biosynthesis, which is essential for maintaining connective tissue integrity, wound healing, and vascular health. Furthermore, vitamin C is involved in the synthesis of neurotransmitters like norepinephrine through its role as a cofactor for dopamine beta-hydroxylase.

On the cellular level, ascorbic acid facilitates iron absorption in the gastrointestinal tract by reducing ferric iron (Fe3+) to the more absorbable ferrous form (Fe2+) and enhances immune function by supporting various cellular activities of leukocytes, including phagocytosis and chemotaxis. Its antioxidant capacity also regenerates other antioxidants such as vitamin E to their active states, promoting a networked cytoprotective effect.

Comparatively, ascorbic acid differs from synthetic antioxidants by its water solubility and specific enzymatic roles, making it indispensable for humans who cannot synthesize it endogenously due to evolutionary loss of the L-gulonolactone oxidase enzyme. Clinical research supports its therapeutic use in preventing and treating scurvy, improving immune response, and mitigating oxidative stress-related diseases. The diverse biochemical actions of ascorbic acid contribute to its broad clinical applications and importance in health maintenance.

Pharmacological Actions

Potent antioxidant activity scavenging reactive oxygen and nitrogen species
Cofactor in enzymatic hydroxylation for collagen synthesis and connective tissue maintenance
Enhances absorption of dietary non-heme iron
Supports immune system function by enhancing leukocyte activity
Involved in neurotransmitter biosynthesis, including norepinephrine
Facilitates regeneration of other antioxidants such as vitamin E
Promotes wound healing and tissue repair
Contributes to cardiovascular health by supporting endothelial function
Acts as a urinary acidifier to prevent certain renal calculi
Modulates inflammatory responses and cellular signaling pathways
Protects against oxidative damage in skin and ocular tissues
Enhances energy metabolism through participation in carnitine synthesis
Improves resistance to infections through immune modulation
Facilitates adrenal gland hormone production
Supports bone matrix formation through collagen stabilization

Therapeutic Clinical Uses

Treatment and prevention of vitamin C deficiency and scurvy
Dietary supplementation to support overall health and antioxidant status
Urinary acidification in specific urological conditions
Supportive therapy in wound healing and tissue repair
Adjunctive use in certain cardiovascular and immune disorders
Used to reduce risk of chronic diseases related to oxidative stress
May be employed for improvement of iron deficiency anemia secondary to poor absorption
Support in recovery and immune enhancement during infections or stress
Potential adjunct in cancer therapy to modulate oxidative stress
Used in management of dermatological conditions benefiting from collagen support
Treatment in burns and surgical recovery to promote healing
Supplementation in elderly or malnourished individuals
Prevention of cold symptoms and reduction of their duration (adjunct)
Management of fatigue and general health maintenance
Supportive therapy in patients undergoing dialysis or with renal disease

Side Or Adverse Effects

Allergic reactions including hives, facial or throat swelling, difficulty breathing
Kidney problems including pain, hematuria, swelling, and potential nephrolithiasis
Gastrointestinal disturbances such as nausea, vomiting, diarrhea, and stomach cramps
Heartburn and dyspepsia
Headache and dizziness reported rarely
Difficulty or painful swallowing in some patients
Risk of iron overload in patients with hemochromatosis when given in high doses
Potential false laboratory test alterations due to interference
Less commonly, increased risk of oxalate kidney stones with excessive dosing
Rare hypersensitivity skin reactions
Potential interactions exacerbating gastrointestinal irritation with NSAIDs
Mild gastrointestinal discomfort may occur with high dose oral administration
Risk of hemolytic anemia in G6PD deficient individuals at high doses
Hypersensitivity reactions to injectable forms
Potential exacerbation of sickle cell crisis with excessive intake

Precautions

Use cautiously in patients with history of kidney stones or renal impairment
Monitor doses carefully in individuals with glucose-6-phosphate dehydrogenase deficiency
Avoid exceeding recommended doses to prevent gastrointestinal upset and nephrolithiasis
Use caution in diabetic patients as high doses may affect glucose test results
Advise patients to inform healthcare providers about all concurrent medications and supplements
Careful assessment in patients with cancer undergoing treatment
Pregnant and breastfeeding women should use only recommended doses and consult healthcare providers
Patients on low-salt diets or with electrolyte imbalances should be monitored
Ensure proper hydration to reduce risk of kidney stone formation
Supervise use in patients undergoing surgery or medical procedures
Avoid use in hypersensitive individuals
Use caution in elderly patients with compromised renal function
Children should use only under medical advice
Use only as directed to avoid overdose
Inform patients about potential side effects and the importance of adhering to recommended doses

Warnings

Do not use if allergic to ascorbic acid
High doses may cause kidney stones, especially in susceptible individuals
Excessive use may cause hemolysis in patients with G6PD deficiency
May interfere with certain laboratory tests leading to misinterpretation
Use under medical supervision in patients with chronic diseases or undergoing surgery
Prolonged high-dose use may induce gastrointestinal symptoms
Avoid overdose as it may lead to toxicity and acute symptoms
Strictly follow dosage instructions to prevent adverse effects
Patients with kidney disease require medical supervision during use
Avoid self-medication for unapproved uses
Potential interactions with chemotherapeutic agents should be assessed
Not recommended to exceed upper limits without physician guidance
Monitor for signs of allergic reactions, seek immediate care if present
Use caution with concurrent use of other vitamins or antioxidants
Ensure secure storage to prevent accidental ingestion by children

Contraindications

Known hypersensitivity to ascorbic acid or any formulation components
Patients with a history of oxalate kidney stones without medical supervision
Severe renal impairment without dose adjustment
Individuals with hemochromatosis or iron overload disorders receiving high doses
Use in individuals with G6PD deficiency without medical counseling
Contraindicated for self-treatment of unconfirmed vitamin C deficiency
Avoid injectable forms in patients with allergy to parenteral vitamin preparations
Contraindicated in patients allergic to excipients in specific formulations
Not for use in individuals with active hyperoxaluria
Avoid overdose in individuals with gastrointestinal ulcers
Contraindicated in persons with a history of severe allergic reactions to vitamin C products
Use cautiously in patients with certain metabolic disorders affecting vitamin C handling
Not recommended in patients with untreated anemia of unknown etiology
Avoid use in patients taking high-dose chemotherapy without medical advice
Do not use in individuals with galactosemia due to excipient content in some preparations

Drug Interactions

May increase absorption and toxicity of iron when coadministered with iron supplements
High doses may reduce the effectiveness of warfarin by interfering with vitamin K metabolism
Vitamin C may alter the renal clearance of some drugs leading to altered plasma levels
Potential interaction with chemotherapy agents affecting treatment efficacy
May decrease the bioavailability of certain protease inhibitors
Vitamin C can interfere with certain urine glucose and blood tests causing false results
Concurrent use with aluminum-containing antacids may reduce vitamin C absorption
May increase the risk of oxalate nephropathy when combined with drugs inducing renal stress
Potential to modify metabolism of levodopa when taken together
Interaction with chlorpromazine affecting its pharmacokinetics
High doses may reduce the effectiveness of estrogens and corticosteroids when used chronically
May increase absorption of tetrahydrocannabinol (THC)
Concomitant use with aspirin may increase gastric irritation
Vitamin C might reduce the effectiveness of protease inhibitors like indinavir
Interactions with herbal products and other vitamins need to be considered and managed

Preparations Of The Drug

Oral capsules: 333.33 mg, 500 mg, 750 mg, 1000 mg (with rose hips, bioflavonoids, citrus bioflavonoids)
Oral capsule extended release: 500 mg
Oral liquid: 500 mg per 5 mL
Oral powder for reconstitution: 500 mg per 4 g
Oral tablets: 250 mg, 500 mg, 1000 mg, 1500 mg (with bioflavonoids and citrus bioflavonoids variants)
Chewable tablets: 60 mg, 120 mg, 125 mg, 250 mg, 500 mg
Orally disintegrating tablets: 100 mg, 250 mg
Approved injectable formulations for intravenous, intramuscular, and subcutaneous administration
Combination formulations with rose hips and various bioflavonoids to enhance efficacy and absorption
Multivitamin preparations containing varying concentrations of ascorbic acid
Vitamin C gummies and effervescent tablets for ease of administration
Time-release and quick melt formulations to optimize plasma levels and patient compliance
Topical preparations containing vitamin C for dermatological uses (outside scope of systemic use)