quote:
Originally posted by HEATHERKISS:
Hey Tree,I checked for any reaction warnings... no problem with biaxin and GSE
Thanks
Thank you everyone. I was a little embarrassed to post this creep crawly symptom but now I'm so glad I did. It's nice to know I'm not alone.
It's so weird that we all have so many strange symptoms and problems.
I thank GOD I can get educated here!
CLINICAL SUMMARY
A water-soluble vitamin necessary for a variety of physiologic functions in the human body. Patients use this supplement as an immune stimulant and antioxidant, to prevent and treat cancer and infections, improve wound healing, and promote heart health. The body cannot synthesize vitamin C. Physiologic processes that require vitamin C include formation of collagen, catecholamines, and carnitine in addition to tyrosine metabolism, peptide synthesis, and antioxidant activity (1). Pharmacokinetic profile is significant for non-linear absorption and elimination, decreased and increased respectively, which occurs with increasing oral doses. Clinical studies suggest no survival advantage or antineoplastic activity with vitamin C. In addition, in vitro and animal studies suggest that cancer cells preferentially uptake vitamin C, suggesting that high dose supplementation may be detrimental for cancer patients undergoing radiation or chemotherapy (7). A recent review of 14 clinical trials shows that supplementation with antioxidants beta-carotene, vitamins A, C, and E does not seem to prevent gastrointestinal cancer and may actually increase overall mortality (18). Three clinical trials in end-stage cancer patients at the Mayo Clinic show no benefit and significant adverse effects from high-dose vitamin C (14). However, low consumption of vitamin C has been associated with increases in adverse effects caused by chemotherapy (19). Some data suggests that vitamin C may reduce the severity and duration of respiratory infections in otherwise healthy patients, although no prophylactic benefit has been demonstrated. A clinical trial in women with coronary artery disease shows an increased risk of death and nonfatal myocardial infarction in patients who took supplements of vitamin C and vitamin E (11). Studies offer conflicting data about the benefit of vitamin C in reducing blood pressure (12) (13). Vitamin C may also offer protection against Alzheimer's disease (10) (15). The daily recommended intake of vitamin C is 75 to 125 mg/day with a tolerable upper limit of 2,000 mg/day. Potential adverse effects are gastrointestinal in nature, although hypoglycemia and hypotension are documented for doses greater than 1 gram per day. Patients with a history of oxalate kidney stones, renal insufficiency, G6PDH deficiency, or hematochromatosis should consult physicians before taking supplements of vitamin C.
SCIENTIFIC NAME
Ascorbic Acid
ALSO KNOWN AS
Ascorbate, sodium ascorbate
FOOD SOURCES
Citrus fruits, cruciferous vegetables, berries, peppers, melons, tomatoes, potatoes (2)
PURPORTED USES
Asthma
Bronchitis
Cancer prevention
Cancer treatment
Cardiovascular disease
Cataracts
Common cold
Glaucoma
Hypertension
Immunostimulation
Infections
Parkinson's disease
Strength and stamina
Wound healing
MECHANISM OF ACTION
A water-soluble antioxidant, vitamin C reacts directly with superoxide, hydroxyl radicals, and singlet oxygen molecules. Ascorbic acid promotes wound healing by serving as a reductant in the pathway for the formation and polymerization of collagen. Vitamin C deficiency thus results in impaired wound healing and scurvy (1). Vitamin C is important for the synthesis of catecholamines and carnitine, in addition to the conversion of folic acid to folinic acid. It is also involved with tyrosine metabolism and peptide synthesis. During a state of infection, vitamin C may reduce inflammation caused by oxidizing chemicals released by phagocytic leukocytes following activation (6). Vitamin C also may inhibit free radical inactivation of nitric oxide, thereby improving endothelium-dependent vasodilation (8).
PHARMACOKINETICS
Absorption:
Intestinal absorption occurs through a sodium-dependent active transport process that is saturable and dose-dependent. Approximately 70-90 percent of the usual dietary intake of ascorbic acid (30-180 mg/day) is absorbed, although absorption falls to 50 percent or less with increasing doses above 1 g/day. The bioavailability of vitamin C from food or supplements is not significantly different.
Distribution:
Dehydroascorbic acid is the form of the vitamin that primarily crosses the membranes of cells, after which it is reduced intracellularly to ascorbic acid. High levels of the vitamin are maintained in the pituitary and adrenal glands, leukocytes, eye tissue and humors, and the brain, while relatively low levels are found in plasma and saliva.
Metabolism / Excretion:
Due to homeostatic regulation, the biological half-life varies widely from 8 to 40 days and is inversely related to body pools. Renal excretion increases proportionally with higher intakes. With large intakes of the vitamin, unabsorbed ascorbate is degraded in the intestine, a process that may account for the diarrhea and intestinal discomfort occasionally reported by people ingesting large doses.
(4)
CONTRAINDICATIONS
Patients who should avoid high dose vitamin C include those with:
Recurrent kidney stone formation
Renal impairment or on chronic hemodialysis
Hematochromatosis
Known G6PDH deficiency
Large doses of vitamin C may induce copper deficiency.
ADVERSE REACTIONS
Common: Nausea, diarrhea, stomach cramps and possible hypoglycemia and hypotension with doses greater than 1 gram.
Reported: In patients with a history of kidney stones, increased oxalate kidney stone formation occurs with possible nephrolithiasis, acute renal failure, or renal insufficiency.
In patients with G6PDH deficiency, hemolytic anemia may occur at high doses (1).
Toxicity: Excessive use of chewable tablets may break down tooth enamel, increasing the risk of dental caries (3).
DRUG INTERACTIONS
Iron: Ascorbic acid increases iron absorption and modulates transport and storage in the body. Significant in patients with hematochromatosis.
(3) (4)
LAB INTERACTIONS
High dose ascorbic acid supplementation may alter results of urine glucose testing strips, and may cause a false negative guaiac (occult blood) test (5).
Drug-Vitamin Interaction
Poor vitamin absorption is a common problem with drug administration.
The effectiveness of vitamins ingested not only from supplements, but also from food, can often be deterred by drug ingestion. One of the most common DNIs occurs with the frequent prescription of antibiotics and the way they can affect the bioavailability of the fat-soluble vitamins (A,D,E,K). Cholestyramine, a drug that is classified as a bile acid sequestrate, can retard the absorption of vitamins A, D and K and bind essential fatty acids as well. Other interactions between drugs and fat-soluble vitamins include:
Vitamin A, Beta-Carotene
*Neomycin can retard absorption
*Ethanol can cause hepatotoxicity resulting in hypervitaminosis A.
*Tetracycline may cause hypertension.
Vitamin D
*Cathartics can retard absorption of vitamin D.
*Glutethimide produces vitamin D deficiency.
Vitamin E
*Dicumarol enhances anticoagulant action.
*Digoxin causes hypercalcemia and arrythmias
Vitamin k
*Anticonvulsants induce enzymatic inactivation.
*Dicumarol inhibits hypoprothrombin action.
Water-soluble vitamins may also be depleted by medication use.
Sometimes it is recommended to ingest the nutrients two hours apart from the prescribed medication to avoid any interaction. However, this rule of thumb may depend on the drug.
Vitamin B 12
*Colchicine impairs B 12 absorption
*Oral contraceptives, Hydralazine, Isoniazid and Penicillamine increase the
requirement for B 6.
Folate
*Aspirin competes with folate for serum protein binding.
*Barbiturates cause malabsorption.
*Primadone interferes with folate metabolism.
Vitamin B 6
*Oral contraceptives cause malabsorption of polyglutamate.
*Cycloserine is secondary to vitamin B6 antagonism.
*Methotrexate inhibits dihydrofolate reductase.
Vitamin C
*Salicylates decrease uptake of vitamin C.
*Tetracyclines deplete vitamin C.