Over-the-counter vitamin and herbal preparations are widely used and considered innocuous by most of the public. Many of these products, however, can produce significant toxicity, especially if used in excess. In addition, many patients neglect to mention or are reluctant to divulge that they are taking these products.
Hypervitaminosis most commonly occurs with supratherapeutic dosing, in part due to lack of public awareness of the harms of excessive use. Ingestion of large doses of fat-soluble vitamins A, D, and E can produce subacute or chronic toxicity. Water-soluble vitamins associated with toxicity include niacin, pyridoxine, and vitamin C. Common symptoms of vitamin toxicities are listed in Table 116-1.
++ Table Graphic Jump Location Table 116-1
Symptoms of Hypervitaminosis
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Symptoms of Hypervitaminosis
|Vitamin ||Symptoms |
|Vitamin A || |
Subacute toxicity: red peeling rash, headache, vomiting
Chronic toxicity: blurred vision, appetite loss, abnormal skin pigmentation, hair loss, dry skin, pruritus, long-bone pain, bone fractures, rare cases of pseudotumor cerebri, hypercalcemia, and hepatic failure
|Vitamin D ||Subacute toxicity: hypercalcemia, anorexia, nausea, abdominal pain, lethargy, weight loss, polyuria, constipation, confusion, and coma |
|Vitamin E ||Chronic toxicity: coagulopathy in patients on warfarin, nausea, fatigue, headache, weakness, and blurred vision |
|Vitamin K ||Acute toxicity: anaphylactoid reactions if given in parenteral form (rare) |
|Vitamin B1 (thiamine) ||No toxicity observed with ingestion of large doses |
|Vitamin B2 (riboflavin) ||No toxicity observed with ingestion of large doses |
|Vitamin B3 (niacin) || |
Acute toxicity: niacin flush, dose >100 mg, redness, burning, and itching of the face, neck, and chest; rarely hypotension
Chronic toxicity: doses >2000 mg/day, abnormalities of liver function, impaired glucose tolerance, hyperuricemia, skin dryness, and discoloration
|Vitamin B6 (pyridoxine) ||Subacute and chronic toxicity: doses >1–3 g/day orally or more over several weeks, peripheral neuropathy with unstable gait, numbness of the feet, similar symptoms in the hands and arms, marked loss of position and vibration senses |
|Vitamin B12 ||No toxicity observed with ingestion of large doses. With large IV doses: erythema of skin, mucous membranes, serum, and urine. Rare anaphylactoid reactions. Possible interference with serum colorimetric lab studies. |
|Folate ||No toxicity observed with ingestion of large doses. Masking of macrocytic anemia from vitamin B12 deficiency with large doses of folate. |
|Vitamin C (ascorbate) ||Chronic toxicity: nephrolithiasis (controversial), intrarenal deposition of oxalate crystals with renal failure; large doses can produce diarrhea and abdominal cramps. |
Many popular herbal preparations have potential for serious toxicity and medication interactions, despite being considered by many to be natural and safe alternatives to Western pharmaceuticals. Lack of regulation of these products raises the potential for toxic contaminants that may independently cause acute poisoning. While generally safe, chamomile, glucosamine, and Echinacea rarely cause anaphylaxis. Other commonly used agents, their uses, and associated adverse events are listed in Table 116-2.