Ascorbic acid (Vitamin C)

Abdelwahab Ward, BS Pharm, PharmD

Vitamin, water soluble.
Mechanism of Action ã…¡ Ascorbic acid is an essential water soluble vitamin that acts as a cofactor and antioxidant. Ascorbic acid is an electron donor used for collagen hydroxylation, carnitine biosynthesis, and hormone/amino acid biosynthesis. It is required for connective tissue synthesis as well as iron absorption and storage.
Sources ã…¡ Orange Juice (8 ounces contains 100 mg), lemons and grapefruit.

  • Prevention and treatment of scurvy (Scurvy develops 1 to 3 months after initiating a vitamin C deficient diet. Complain of lethargy, fatigue, malaise, emotional lability, arthralgias, weight loss, anorexia, and diarrhea. Patient may experience easy bleeding, bruising, and poor wound healing). Its parenteral administration is desirable for patients with an acute deficiency or for those whose absorption of orally ingested ascorbic acid (vitamin C) is uncertain.
  • Symptoms of mild deficiency may include faulty bone and tooth development, gingivitis, bleeding gums, and loosened teeth. Febrile states, chronic illness, and infection (pneumonia, whooping cough, tuberculosis, diphtheria, sinusitis, rheumatic fever, etc) increase the need for ascorbic acid (vitamin C).
  • Hemovascular disorders, burns, delayed fracture and wound healing are indications for an increase in the daily intake.
  • Recommended daily allowance: 40 to 120 mg, depending on age and gender.
  • Treatment of scurvy: 100 to 300 mg daily, increase the dose to 1 g daily until symptoms remit. Clinical improvement is noted within the first 1 to 2 weeks, with a resolution of fatigue, joint swelling, ecchymoses, and gingiva healing. Complete recovery frequently occurs within three.
  • Formula fed infants: 35 mg/day.
  • Lactating mothers: 100 mg/day.
  • Other children and adults: 45-60 mg/day.
  • Vitamin C supplementation is contraindicated in blood disorders like thalassemia, G6PD deficiency, sickle cell disease, and hemochromatosis. Avoid taking supplements immediately before or following angioplasty. Diabetic patients should take vitamin C supplements with care as it raises blood sugar levels.
  • Vitamin C should be used cautiously in oxalate nephropathy or nephrolithiasis as acidification by ascorbic acid increases the chances of precipitation of cysteine, urate, and oxalate stones.
  • Onset of action: Reversal of scurvy symptoms: 2 days to 3 weeks.
  • Absorption: Oral; Readily absorbed in the intestine; an active process thought to be saturable and dose dependent (30 to 180 mg/day: 70% to 90%; > 1,000 mg/day: ≤ 50%).
  • Bioavailability: Oral; For doses up to 200 mg, nearly 100%; declines with increasing doses with ~33% for a single dose of 1250 mg.
  • Distribution: Pituitary and adrenal glands, leukocytes, eye tissues and humors, and brain; lower concentrations in the plasma and saliva.
  • Metabolism: Reversibly oxidized to dehydroascorbic acid (DHA); both ascorbic acid and DHA are active. Unabsorbed ascorbic acid is degraded in the intestine.
  • Half-life elimination: 10 hours. Biological half-life: 8 to 40 days.
  • Excretion: Urine (with high serum concentrations), there is an individual specific renal threshold for ascorbic acid; when blood levels are high, ascorbic acid is excreted in urine, whereas when the levels are subthreshold (doses up to 80 mg/day) very little if any ascorbic acid is excreted into urine.
  • Adverse effects include headaches, flushing, nausea or vomiting, and dizziness (IV use). There are reports of migraine headaches with a daily dose of 6 g.
  • Significant amounts of vitamin C can increase the risk of kidney stones and elevate uric acid and oxalate because it acidifies the urine.
  • Test interactions ã…¡ (1) False-negative stool occult blood 48 to 72 hours after ascorbic acid ingestion. (2) May interfere with laboratory tests based on oxidation-reduction reactions (e.g., blood and urine glucose testing, nitrite and bilirubin levels, leucocyte count). If possible, laboratory tests based on oxidation-reduction reactions should be delayed until 24 hours after dose.
Abdelwahab Ward, BS Pharm, PharmD