Usage
- Medical Conditions: Vitamin C is primarily used to prevent and treat scurvy. It is also used as a dietary supplement in individuals who do not obtain enough vitamin C in their diet, as an adjunct therapy in methemoglobinemia and, although evidence supporting efficacy is inconclusive, sometimes in sepsis and acute respiratory distress syndrome.
- Pharmacological Classification: Vitamin, antioxidant, and enzyme cofactor.
- Mechanism of Action: Vitamin C is an essential cofactor for various enzymatic reactions, including collagen synthesis, carnitine biosynthesis, and catecholamine synthesis. It also acts as an antioxidant, scavenging free radicals. In methemoglobinemia, it reduces methemoglobin to hemoglobin.
Alternate Names
- Ascorbic acid, L-ascorbic acid
- Brand names vary depending on the manufacturer. Examples include Limcee, Celin, and Redoxon.
How It Works
- Pharmacodynamics: Vitamin C exerts its effects through its role as a cofactor in enzymatic reactions and as an antioxidant. In collagen synthesis, it is essential for the hydroxylation of proline and lysine residues, contributing to the structural integrity of connective tissue. In carnitine biosynthesis, it participates in the conversion of trimethyllysine to carnitine, important for fatty acid transport into mitochondria for energy production. In catecholamine synthesis, it facilitates the conversion of dopamine to norepinephrine. Its antioxidant effects are attributed to its ability to donate electrons, neutralizing free radicals.
- Pharmacokinetics: Vitamin C is absorbed in the small intestine, where the process is saturable. It is distributed widely throughout the body. The liver metabolizes excess vitamin C into inactive metabolites, which are excreted renally.
- Mode of Action: At the cellular level, vitamin C participates in various redox reactions, donating electrons to neutralize reactive oxygen species, thus protecting cells from oxidative damage. It is also involved in hydroxylation reactions, influencing enzymatic activity and protein structure.
- Elimination Pathways: Primarily renal excretion.
Dosage
Standard Dosage
Adults: The recommended daily allowance (RDA) for adults is 90 mg/day for men and 75 mg/day for women. Smokers require an additional 35 mg/day. For treatment of scurvy, 250-1000 mg daily is recommended, orally or intravenously.
Children: Dosing for children is based on age, ranging from 40-90 mg/day.
Special Cases:
- Elderly Patients: Same as adult dosage.
- Patients with Renal Impairment: Dose adjustment may be required in severe renal impairment.
- Patients with Hepatic Dysfunction: No specific dose adjustments are usually necessary.
- Patients with Comorbid Conditions: No specific dose adjustments are usually necessary.
Clinical Use Cases
Dosages higher than the RDA are used in specific clinical situations:
- Intubation, Surgical Procedures, Mechanical Ventilation, ICU Use: Dosages ranging from 1-6 g/day intravenously have been studied in critically ill patients to potentially shorten ICU stay and duration of mechanical ventilation. Evidence supporting efficacy is currently mixed.
- Emergency Situations: High-dose intravenous vitamin C has been studied in some emergency settings like sepsis and cardiac arrest. Further trials are needed to provide definitive guidance.
Dosage Adjustments
Dose adjustments may be needed in renal impairment or for individuals taking high doses of vitamin C chronically.
Side Effects
Common Side Effects
High doses (>2000 mg/day) can cause diarrhea, nausea, abdominal cramps, and headache.
Rare but Serious Side Effects
Kidney stones in susceptible individuals, hemolysis in individuals with G6PD deficiency.
Long-Term Effects
Long-term excessive intake can potentially contribute to kidney stone formation.
Adverse Drug Reactions (ADR)
Most ADRs are related to gastrointestinal intolerance. Rarely, allergic reactions have been reported.
Contraindications
- History of kidney stones (especially in high doses)
- G6PD deficiency (in high doses)
- Hypersensitivity to ascorbic acid
Drug Interactions
- Deferoxamine: Concurrent administration can exacerbate iron toxicity.
- Warfarin: Vitamin C may reduce the anticoagulant effect of warfarin.
- Fluphenazine: Vitamin C can decrease fluphenazine plasma concentrations.
Pregnancy and Breastfeeding
Vitamin C is considered safe during pregnancy and breastfeeding at recommended doses. Excessive intake should be avoided.
Drug Profile Summary
- Mechanism of Action: Cofactor in enzymatic reactions, antioxidant.
- Side Effects: Diarrhea, nausea, abdominal cramps (high doses).
- Contraindications: Kidney stones, G6PD deficiency, hypersensitivity.
- Drug Interactions: Deferoxamine, warfarin, fluphenazine.
- Pregnancy & Breastfeeding: Generally safe at RDA.
- Dosage: RDA: 90 mg/day (men), 75 mg/day (women). Scurvy: 250-1000 mg/day. Higher doses used in clinical settings, but evidence is inconclusive.
- Monitoring Parameters: In critically ill patients receiving high-dose vitamin C, renal function and glucose levels should be monitored.
Popular Combinations
Vitamin C is sometimes combined with other vitamins and minerals in multivitamin formulations or with specific medications for conditions like methemoglobinemia (methylene blue).
Precautions
Monitor for gastrointestinal side effects and kidney stones with high-dose use. Evaluate for G6PD deficiency before administering high doses intravenously.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Vitamin C?
A: The RDA for adults is 90 mg/day for men and 75 mg/day for women. Higher doses may be appropriate for specific clinical indications (e.g., scurvy).
Q2: Can Vitamin C be given intravenously?
A: Yes, intravenous administration is used for scurvy treatment and also investigated in some critical care settings, but the evidence is mixed.
Q3: What are the signs and symptoms of scurvy?
A: Fatigue, weakness, aching limbs, swollen and bleeding gums, petechiae, and impaired wound healing.
Q4: Does Vitamin C interact with any medications?
A: Yes, potential interactions exist with deferoxamine, warfarin, and fluphenazine.
Q5: Is Vitamin C safe during pregnancy?
A: Yes, vitamin C is considered safe during pregnancy at the RDA.
Q6: Can Vitamin C cause kidney stones?
A: High-dose vitamin C intake can increase the risk of kidney stones, particularly in individuals with pre-existing conditions like hyperoxaluria.
Q7: What is the role of Vitamin C in sepsis?
A: High-dose intravenous vitamin C is being studied as a potential adjunctive therapy in sepsis, but there is no conclusive evidence to support its routine use as of February 17, 2025.
Q8: What is the role of Vitamin C in acute respiratory distress syndrome (ARDS)?
A: Vitamin C is being studied in patients with ARDS, particularly those requiring mechanical ventilation, due to its potential to reduce inflammation and oxidative stress.
Q9: Can Vitamin C treat the common cold?
A: While some studies suggest vitamin C may slightly reduce the duration or severity of a cold, the evidence is not conclusive. It does not prevent the common cold.
Q10: What are the best food sources of Vitamin C?
A: Citrus fruits (oranges, grapefruits, lemons), berries (strawberries, blueberries), peppers, tomatoes, potatoes, and leafy green vegetables.
