Antivitamins or vitamin antagonists
Research in the chemical structure of vitamins has led logically to more understanding about their characteristic reactions. Some are destroyed by oxidation or light or are inactivated by reaction with other compounds. Any substance that prevents the absorption or metabolic functioning of a vitamin in the body is called an antivitamin or a vitamin antagonist; for example, avidin is an antagonist ro biotin. One type of antagonist is a compound so similar in chemical structure to the vitamin that it starts to react like the true vitamin but cannot finish the reaction, thereby blocking the space where the real vitamin could function.
An interesting example of this type of reaction is a folic acid antagonist, which has been used clinically in the treatment of malignant growths. The theory is that rapidly dividing cells may need more folic acid than normal cells, and, therefore, an antagonist might inhibit growth of the abnormal cells. Unfortunately, the folic acid antagonist inhibits growth in normal as well as in abnormal cells.
Antibiotics and, possibly, some of the sulfa drugs used in the treatment of infections may be vitamin antagonists. Normally, bacteria in the intestinal tract have the ability to synthesize certain vitamins. When a sulfa drug or an antibiotic is given orally, it may make some of the intestinal bacteria incapable of vitamin synthesis, thereby inhibiting growth. Conversely, in other animals antibiotics seem to stimulate grm.vth by changing the balance of the intestinal microorganisms
