Medicine: How Sulfa-Drugs Work

Without any real understanding of how sulfa-drugs overcome infections, doctors have been freely using them ever since Dr. Gerhard Domagk of Germany discovered prontosil, forerunner of sulfanilamide, in 1932.* But the mystery of their effectiveness has recently been cleared up by a series of discoveries reviewed in a recent issue of the British Medical Journal.

Discoverer of the mechanism of sulfa-therapy is Bacteriologist Paul Fildes of London. Certain bacteria, he found, mistake the sulfa-drugs for a vitaminlike substance—probably of the vitamin B complex—which they need for growth. Consuming the pseudo-vitamin instead of the real, the bacteria fail to multiply, so that the blood’s white corpuscles can easily destroy their limited numbers. How slight is the lethal error which the bacteria make is shown by the similar chemical names: sulfanilamide is para-amino-benzene-sulfonamide; the growth factor is para-amino-benzoic acid.

Fildes’s discovery has already helped other researchers to further advances in chemotherapy :

> Many bacteria need another B factor, pantothenic acid, to thrive. So Bacteriologist Henry McIlwain of Sheffield, England, reasoned that bacteria might likewise mistake a compound called pantoyltaurine for its chemical relative, pantothenic acid. His hunch was right, and his discovery may well lead to development of a second group of bacteria-hoaxing chemicals comparable to the sulfa-group.

> Since it is largely the similar acid properties of the sulfa-drugs and the bacterial vitamins which confuse the bacteria, Chemists Richard O. Roblin Jr. and Paul H. Bell (of the sulfa-making American Cyanamid Co.) have developed a method of measuring the acidity of the several hundred possible sulfa-compounds and thus ‘predicting their efficacy. But such predictions are complicated by other factors: some sulfa-drugs are not absorbed by the body and thus never reach the blood stream; others undergo chemical changes in the body and thus lose their powers.

Many of the sulfa-powders marketed in the U.S. were recently found to be contaminated with assorted bacteria (mostly harmless). Upshot: the U.S. Food & Drug Administration now requires all sulfa-powders to be heat-sterilized and carefully packaged. At least one person has already died of tetanus when unsterile sulfapyradine was used following a pelvic operation. Tetanus germs are among the group which sulfa-drugs do not affect.

* In 1939, at a frown from the Nazis, Domagkrejected a $40,000 prize from the fund established by the peace-loving inventor of dynamite,Alfred Nobel.