Vitamins: Deficiencies and Drug Interactions



Vitamins: Deficiencies and Drug Interactions



Overview


Vitamin deficiencies have various causes, including an inadequate supply of the vitamin in the diet, inability of the body to absorb or utilize the vitamin, excessive degradation or excretion of the vitamin, general nutritional deficiency, disease, and vitamin-drug interactions.


Vitamins are commonly classified into those that are water soluble and those that are fat soluble. Water-soluble vitamins include the vitamin B family—thiamine (B1), riboflavin (B2), nicotinic acid (niacin) (B3), pyridoxine (B6), pantothenic acid, cyanocobalamin (B12), biotin, and folic acid (folacin)—and vitamin C (ascorbic acid). Fat-soluble vitamins include vitamin A (retinol); the vitamin D family—calciferol (D2) and cholecalciferol (D3); vitamin E (α tocopherol); and the vitamin K family—phylloquinone (K1), menaquinones (K2), and menadione (K3).


Water-soluble vitamins typically have small body stores, and thus, the concentrations of these vitamins can readily be compromised in the presence of alcoholism, dieting (fads), prolonged anorexia, nausea, dysphagia, diarrhea, weight loss, advanced organ failure, and malabsorption. Fat-soluble vitamins are affected by any chronic deficiency in fat absorption, such as that occurring in short bowel syndrome, pancreatic insufficiency, bacterial overgrowth, celiac sprue, Whipple disease, and primary biliary cirrhosis.


Management of vitamin deficiency disorders can take many forms, including prevention (maintenance of adequate dietary intake), supplementation (usually oral, but the parenteral route is also used), treatment of an underlying disorder, and elimination of interactions with drugs.


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Figure 13-1 Deficiency of Vitamin A (Retinol) and Other Fat-Soluble Vitamins
Dietary sources of the fat-soluble vitamin A include milk fat, eggs, green leafy or yellow vegetables, and fish oil. Vitamin A is formed from precursors (α, β, and γ carotenes) found in yellow pigments of fruits and vegetables (eg, apples, cabbage, cantaloupes, carrots, oranges, tomatoes). Diseases that result in malabsorption of fat or impaired storage of vitamin A in the liver are characterized by interference with growth, reduced resistance to infections, and disrupted epithelial cell structure and function. Principal manifestations of this deficiency include xerophthalmia (conjunctival dryness with epithelial keratinization), night blindness, and hyperkeratinization of skin. The main manifestations of other fat-soluble vitamin deficiencies include rickets (vitamin D), excessive steatorrhea (secretion of fat from sebaceous glands of skin; fatty stools) (vitamin E), and increased bleeding time (vitamin K). All these deficiencies are treated via supplementation.
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Jun 21, 2016 | Posted by in PHARMACY | Comments Off on Vitamins: Deficiencies and Drug Interactions

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