1. Clinical Overview
Vitamin C (Ascorbic Acid) is a water-soluble vitamin essential for collagen synthesis, antioxidant defense, and immune function. In the Indian context, a 75mg dose is commonly used for daily nutritional supplementation, prophylaxis, and as adjunctive therapy in conditions with increased oxidative stress or mild deficiency. It is a critical cofactor for enzymes involved in neurotransmitter synthesis, carnitine production, and iron absorption.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral: 2-3 hours for peak plasma concentration; Parenteral: Immediate. | Approximately 24 hours, depending on body stores and dietary intake. Saturation of body stores (approx. 1500mg) leads to rapid renal excretion. | Oral: 70-90% at low to moderate doses (up to 180mg/day). Bioavailability decreases significantly with single doses exceeding 1g due to saturable active transport in the intestine. |
2. Mechanism of Action
Vitamin C acts as an essential cofactor for multiple enzymatic reactions, primarily those involving hydroxylation. It is a potent water-soluble antioxidant that scavenges reactive oxygen and nitrogen species, thereby protecting cellular components from oxidative damage. It also regenerates other antioxidants like Vitamin E.
3. Indications & Uses
- Prevention and treatment of Vitamin C deficiency (Scurvy).
- Dietary supplementation in individuals with inadequate dietary intake (common in low-socioeconomic groups, elderly, and those with restricted diets in India).
4. Dosage & Administration
Adult Dosage: Prophylactic: 75-100mg orally once daily. Therapeutic (for deficiency): 250-500mg daily in divided doses for at least 2 weeks, then maintenance dose.
Administration: Administer orally, preferably with or after meals to reduce gastrointestinal irritation. Tablet/Capsule should be swallowed whole with a glass of water. Chewable or dispersible forms are available. Avoid taking close to antacids containing aluminum (may increase aluminum absorption).
5. Side Effects
Common side effects may include:
- Nausea
- Abdominal cramps/pain
- Heartburn
- Diarrhea (especially with doses >1g)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Oral Iron Supplements (Ferrous sulfate/fumarate) | Vitamin C enhances the absorption of non-heme iron, increasing its bioavailability by 2-3 times. | Moderate |
| Aspirin and NSAIDs | May decrease Vitamin C renal tubular reabsorption, increasing its excretion and potentially lowering body stores. | Mild |
| Oral Contraceptives (Estrogen) | Estrogen may increase Vitamin C requirements and decrease plasma ascorbate levels. | Mild |
| Warfarin | Theoretical interaction; high-dose Vitamin C may slightly reduce anticoagulant effect, but not clinically significant at 75mg. | Minor |
| Aluminum-containing Antacids | Vitamin C may increase aluminum absorption, potentially leading to toxicity in renal impairment. | Moderate (in renal disease) |
| Chemotherapy (e.g., Bortezomib, Doxorubicin) | Antioxidants may theoretically interfere with the oxidative mechanism of some chemotherapeutic agents. Consult oncologist. | Major |
7. Patient Counselling
- DO take as directed, usually once daily.
- DO take with food if you experience stomach upset.
- DO inform your doctor if you are taking iron supplements or have kidney stones.
- DO NOT crush or chew sustained-release capsules unless instructed.
- DO NOT take mega-doses (>1g/day) without medical supervision.
- DO store in a cool, dry place away from light and moisture.
8. Toxicology & Storage
Overdose: Acute overdose is unlikely due to efficient renal clearance. Symptoms of excessive intake (>2g single dose) include severe diarrhea, nausea, abdominal cramps, and flatulence. Chronic megadosage can lead to oxalate nephrolithiasis, hemolysis (in G6PD deficient), iron overload, and conditioned deficiency.
Storage: Store below 30°C, in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the packaging.