Ehrlich's Magic Bullets 1910 – Targeting Chemical Receptors

In 1900, there were few drugs to fight infectious diseases. A famous example is quinine, which Europe had used since 1630 to treat malaria, a disease caused by a protozoan parasite carried by mosquitoes. 

Mercury had been used since 1495 to treat syphilis, a sexually transmitted bacterial disease. However, mercury treatments could be highly toxic to humans. The search therefore continued for chemical agents that would exhibit selective toxicity against the causes of infection while protecting the patient. The work of German scientist Paul Ehrlich, one of the celebrated founders of modern chemotherapy, pioneered this search. Of course, Ehrlich's highly systematic search for such useful chemicals could not have been undertaken before disease-associated microorganisms were identified and germ theory was established in the late 1800s.

Ehrlich wanted to selectively destroy Treponema pallidum, the cause of syphilis, and was particularly interested in arsenic compounds for this purpose. He directed his army of researchers to test countless arsenic compounds every day. 

In 1909, Japanese bacteriologist Sahachiro Hata, who worked in Ehrlich's laboratory and specialised in testing rabbits with syphilis, discovered that arsenic compound no. 606 was effective against the disease. In 1910, Ehrlich announced the discovery of 606 to the world. Marketed as Salvarsan, 606 was the first practical success of Ehrlich's search for chemotherapeutic agents that he called magic bullets. 

The magic bullet analogy refers to Ehrlich's belief that such drugs, which did not harm host cells, functioned as selective weapons aimed at particular chemical receptors present on a parasite.

According to science writer John Simmons, "While Louis Pasteur and Robert Koch developed germ theory, Paul Ehrlich was responsible for the generalisation that disease is fundamentally chemical.”

Interestingly, some church officials opposed Ehrlich's magic bullet on the grounds that sexually transmitted diseases were divine punishment for immorality. In the 1940s, penicillin began to be used to treat syphilis.

Description of the article image: Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum.

Historical figures mentioned in the article: Paul Ehrlich (1854–1915), Sahachiro Hata (1873–1938)

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