ASCORBIC ACID, VITAMIN C

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 darkenupon light exposure. Slight discoloration does not affect potency. Because with time ascorbic acidwill decompose with the production of CO2, open ampules and multidose vials carefully. To reducethe 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 uponfactors such as pH, concentration, temperature and diluents used. It is suggested to consultspecialized references (e.g., Handbook on Injectable Drugs by Trissel; see bibliography) for morespecific information.

Pharmacology - ASCORBIC ACID, VITAMIN C

Exogenously supplied ascorbic acid is a dietary requirement in some exoticspecies (including rainbow trout, Coho salmon), guinea pigs, and in primates. The other domesticspecies are able to synthesize in vivo enough Vitamin C to meet their nutritional needs. Vitamin C isused 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 isbelieved 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 - ASCORBIC ACID, VITAMIN C

Vitamin C is generally well absorbed in the jejunum (human data) after oraladministration, but absorption may be reduced with high doses as an active process is involved withabsorption. 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 bloodconcentrations exceed the renal threshold the drug is more readily excreted unchanged into theurine.

Contraindications, Precautions, Reproductive Safety

Vitamin C (high doses) should be usedwith caution in patients with diabetes mellitus due to the laboratory interactions (see below) or inpatients susceptible to urolithiasis. The reproductive safety of vitamin C has not been studied, but itis 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 forurate, 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 ofsome drugs (e.g., mexiletine, quinidine) and reduce the efficacy of some antimicrobials in theurine (e.g., aminoglycosides, erythromycin). Vitamin C may be synergistic with deferoxaminein 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-dependentstool occult blood test. Vitamin C may decrease serum bilirubin concentrations.