Antivitamins

 Antivitamins

The term antivitamin is loosely used and it refers to substances which have got any of the following three kinds of actions interfering with the normal utilization of this vitamin. These are as follows:

1. These substances have got structural and chemical groups similar to vitamins but without any physiological action. They act as antagonists and in most cases produce deficiency symptoms when given simultaneously with the vitamin. Some of these antivitamins have been pre pared, such as pyrithiamine-pyridine analogue of thiamine. Experimentally and clinically they are of some use.

2. Substances which destroy vitamins, e.g., the enzyme thiaminase destroying thiamine.

3. Some chemical substances make the vitamins ineffective, such as avidin found in raw egg-white which binds and prevents the action of biotin.

Substances having antivitamin activity in case of thiamine are pyrithiamine, oxythiamine and the 2-N-butyl homologue of thiamine.

 Galactoflavin is a potent riboflavin inhibitor. Other compounds are the diethyl derivative, flavin monosulphate, etc., which act as the antagonist to riboflavin in different species.

Niacin antagonists are pyridine-3-sulphonic acid and 3-acetyl pyridine and 6-aminoniacinamide which produce niacin deficiency symptoms in rats.

Pantoyltaurine and -methyl pantothenic acid are the examples of pantothenic acid antagonists.

Deoxypyridoxine plays a potent antagonistic action against pyridoxine. Other examples are methoxypyridoxine and toxopyrimidine.

One of the most important inhibitors of folic acid is aminopterin. Amethopterin also produces deficiency of the folic acid.