[1] It is a good antibacterial drug, but its water solubility is very pH dependent.

As with other sulfonamides, there is a significant risk of agranulocytosis, and this, rather than the development of resistance by bacteria, is the main reason for its decline in use.

It was discovered by Lionel Whitby at the British firm May & Baker Ltd and logged in their Test Book on 2 November, 1937 under Code No M&B 693.

During the aftermath to the disastrous convoy SC7, in October 1940, Surgeon-Lieutenant John Robertson, RN, of HMS Leith, saved the life of Commodore Lachlan MacKinnon, from the torpedoed Assyrian, who had developed pneumonia, by giving him M&B 693, despite Robertson never having used it before and not knowing the required dosage.

[3][4] The same source records that in 1944 M&B 693 also saved Nero, the Royal Circus lion, from pneumonia.