Chemistry - A water soluble vitamin, ascorbic acid occurs as white to slightly yellow crystal or powder. It is freely soluble in water and sparingly soluble in alcohol. The parenteral solution has a pH of 5.5-7.
Storage/Stability/Compatibility - Protect from air and light. Ascorbic acid will slowly darken upon light exposure. Slight discoloration does not affect potency. Because with time ascorbic acid will decompose with the production of CO2, open ampules and multidose vials carefully. To reduce the potential for excessive pressure within ampules, store in refrigerator and open while still cold.
Ascorbic acid for injection is compatible with most commonly used IV solutions, but is incompatible with many drugs when mixed in syringes or IV bags. Compatibility is dependent upon factors such as pH, concentration, temperature and diluents used. It is suggested to consult specialized references (e.g., Handbook on Injectable Drugs by Trissel; see bibliography) for more specific information.
Pharmacology - Exogenously supplied ascorbic acid is a dietary requirement in some exotic species (including rainbow trout, Coho salmon), guinea pigs, and in primates. The other domestic species are able to synthesize in vivo enough Vitamin C to meet their nutritional needs. Vitamin C is used for tissue repair and collagen formation. It may also be involved with some oxidation-reduction reactions, and is involved with the metabolism of many substances (iron, folic acid, norepinephrine, histamine, phenylalanine, tyrosine, some drug enzyme systems). Vitamin C is believed to play a role in protein, lipid and carnitine synthesis, maintaining blood vessel integrity, and immune function.
Uses/Indications - Ascorbic acid may be used as a urinary acidifier, but its efficacy is in question. Sodium ascorbate does not acidify the urine. It is also used to treat copper-induced hepatopathy in dogs.
Pharmacokinetics - Vitamin C is generally well absorbed in the jejunum (human data) after oral administration, but absorption may be reduced with high doses as an active process is involved with absorption. Ascorbic acid is widely distributed and only about 25% is bound to plasma proteins. Vitamin C is biotransformed in the liver. When the body is saturated with vitamin C and the blood concentrations exceed the renal threshold the drug is more readily excreted unchanged into the urine.
Contraindications/Precautions/Reproductive Safety - Vitamin C (high doses) should be used with caution in patients with diabetes mellitus due to the laboratory interactions (see below) or in patients susceptible to urolithiasis. The reproductive safety of vitamin C has not been studied, but it is generally considered to be safe at moderate dosages.
Adverse Effects/Warnings - At usual doses vitamin C has minimal adverse effects. Occasionally GI disturbances have been noted in humans. At higher dosages, there is an increased potential for urate, oxalate or cystine stone formation, particularly in susceptible patients.
Overdosage/Acute Toxicity - Very large doses may result in diarrhea and potentially urolithiasis. Generally, treatment should consist of monitoring and keeping the patient well hydrated.
Drug Interactions - Large doses causing acidification of urine may increase the renal excretion of some drugs (e.g., mexiletine, quinidine) and reduce the efficacy of some antimicrobials in the urine (e.g., aminoglycosides, erythromycin). Vitamin C may be synergistic with deferoxamine in removing iron, but may in fact, lead to increased iron tissue toxicity especially in cardiac muscle. It should be used with caution, particularly in patients with preexisting cardiac disease.
Laboratory Considerations - Large doses may cause false-negative urine glucose values. False-negative results may occur if vitamin C is administered within 48-72 hours of an amine-dependent stool occult blood test. Vitamin C may decrease serum bilirubin concentrations.
For replacement therapy after stress (e.g. strenuous exercise): 20 grams PO daily (Ferrante and Kronfeld 1992)
Dosage Forms/Preparations/FDA Approval Status/Withholding Times -
Parenteral Injection 250 mg/ml in 100 and 250 ml vials; Generic (Rx or OTC depending on labeling)
As ascorbic acid or sodium ascorbate: Oral tablets 25 mg, 50 mg, 100 mg, 250 mg, 500 mg, 1000 mg; chewable tablets: 60 mg, 100 mg, 250 mg, 500 mg,; (various); (OTC)
Oral extended release
capsules and tablets 500 mg; 1000 mg, 1500 mg; (various); (OTC)
Crystals/Powder: 4 g/tsp (in 100 & 500g); 5 g/tsp (in 180 g); (OTC)
mg/0.6ml, 100 mg/ml, (OTC)
Parenteral Injection 250 mg/ml in 2 ml ampules and 30 & 50 ml multidose vials; various & generic; (Rx)
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