Vitamin antagonists

Warfarin is a K-vitamin antagonist used to decrease blood clothing and reduce risk of thrombosis. Warfarin has a narrow therapeutic interval. Food with a high K-vitamin content such as green leaf vegetables, strawberries, liver etcetera counteract the Warfarin effects. 

It should be noted that deficiency states for some vitamins (e.g., pantothenic acid) are practically unknown in human beings. In such cases, deficiency states may be simulated by feeding the subject an appropriate vitamin antagonist. In another series of situations, vitamin deficiencies can be brought about by interfering with their absorption intentionally or may be the result of a disease process. Thus, fat-soluble vitamin deficiency may develop in cases of fat malabsorption syndromes (steatorrhea) sprue, pancreatic insufficiency, and bile duct obstruction. 

Pantothenic acid and its derivatives have essentially no pliarmacological actions per se. Because of the ubiquitous nature of the vitamin, deficiency stales usually do not develop. They have been produced by u.se of synthetic diets devoid of the vitamin or by use of a vitamin antagonist. [Pg.888]

Antivitamins (vitamin antagonists) are substances that specifically decrease or inhibit the action of a vitamin (e.g. Actinomycin is a vitamin D antagonist). Vitamins are not remedies in the usual sense, because vitamin supply with food is a necessary condition for the... 

This system differs from the one which phosphorylates adenosine, because here adenosine diphosphate can also act as a phosphate donor. The enzyme is inert with isoriboflavin, and it does not catalyze the synthesis of flavinadenine dinucleotide. However, it does phosphorylate arabityl flavin and dichloroflavin, both of which are vitamin antagonists. A preparation from the small intestine of rats carries out the same reaction, but is active only with ATP. ... 

Antivitamins (vitamin antagonists) are those substances that eliminate the biological effects of vitamins, which can lead to defidency symptoms. Antivitamins are dealt with in detail in Chapter 5. 

Antivitamins (Vitamin Antagonists, or Pseudo-vitamins). Antivitamins, which are present in some natural foods, are compounds that do not function as vitamins even though they are chemically related to them. As a result, they may cause vitamin deficiencies if the E)ody (1) is unable to distinguish between them and true vitamins, and (2) incorporates them into essential body compounds. 

A substance so similar in structure to the vitamin that the body accepts it in place of the vitamin is known as a vitamin antagonist. But the antagonist is unable to perform the functions of the true vitamin. 

I6I C. Warfarin baits need contain only 0 025% active principle, and rats are killed after ingesting about 5 doses the bait can be left down and the risk of acute toxicity to man or domestic animals is not serious. In common with other coumarin derivatives, warfarin reduces the clotting power of blood and death is caused by haemorrhages initiated by any slight injury. Warfarin is a vitamin K antagonist, and large oral doses of the vitamin can be given as an antidote. 

Many plant substances possess antivitamin D activity but the mode of action and in most cases the identity remain unknown. Rachitogenic factors have been observed in yeast. Because of the metaboHc interrelationships that exist between vitamin D, Ca, and P, it is sometimes difficult to differentiate between chelators of mineral elements and tme antivitamins. One reported vitamin D antagonist in oats was later identified as phytic acid (72). 

Table 16. Retinoic Acids, Vitamin D, and Type II Receptor Agonists and Antagonists...

The principal OTC pharmaceutical products include cold remedies, vitamins and mineral preparations, antacids, analgesics, topical antibiotics, antiftingals and antiseptics, and laxatives. Others include suntan products, ophthalmic solutions, hemorrhoidal products, sleep aids, and dermatological products for treatment of acne, dandmff, insect parasites, bums, dry skin, warts, and foot care products (11). More recent prescription-to-OTC switches have included hydrocortisone, antihistamine and decongestant products, antiftingal agents, and, as of 1995, several histamine H2-receptor antagonists. 

Over 250 analogues of the B vitamers have been reported (11,100). Nearly all have low vitamin B activity and some show antagonism. Among these are the 4-deshydroxy analogue, pyridoxine 4-ethers, and 4-amino-5-hydroxymeth5i-2-methyipyrimidine, a biosynthetic precursor to thiamine. StmcturaHy unrelated antagonists include dmgs such as isoniazid, cycloserine, and penicillamine, which are known to bind to pyridoxal enzyme active sites (4). 

The isoprene-derived molecule whose structure is shown here is known alternately as Coumarin and warfarin. By the former name, it is a widely prescribed anticoagulant. By the latter name, it is a component of rodent poisons. How can the same chemical species be used for such disparate purposes The key to both uses lies in its ability to act as an antagonist of vitamin K in the body. 

Therapeutic Function Anticoagulant, Vitamin K antagonist Chemical Name 3-(Q -acetonyl-p-nitrobenzyl)-4-hydroxycoumarin Common Name Nicoumalone Structural Formula ... 

The pharmacological and/or adverse effects of a drug can be reversed by co-administration of drugs which compete for the same receptor. For example, an opioid receptor antagonist naloxone is used to reverse the effects of opiates. Drugs acting at the same site with opposite effects also can affect each other, e.g. the reduction in the anticoagulant effect of warfarin by vitamin K. 

Vitamin K. Figure 1 The vitamin K cycle, w indicates where warfarin or other vitamin K antagonist inhibit the cycle. 

Application of vitamin K-antagonistic anticoagulants like warfarin gave no clearcut results concerning bone density or a changed risk for bone fractures. 

In contrast to the formation and calcification of bones, vitamin K seems to lower the risk of aortic calcification. The mechanisms for these antagonistic effects is not known but a participation of osteocalcin (expressed in artherosclerotic plaques) as well as of matrix Gla protein (MGP) are discussed. In addition, the vitamin K epoxide reductase complex seems to be involved [5]. 

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