PANTOTHENIC ACID 



the molar concentration of inhibitor to that of promoter necessary to 

 produce inhibition of growth. He obtained the following results : 



DL-Pantoyltaurine DL-Pantoyltauramide 



Pantoyltaurine was believed to act by displacing pantothenic 

 acid from an essential enzyme system and so preventing it from 

 functioning (see page 390), and it was hoped that a new therapeutic 

 agent, equal in importance to the sulphonamides, might have resulted. 

 In fact, this hope was not realised, and neither pantoyltaurine nor its 

 many derivatives (page 397) appear to be capable of inhibiting the 

 growth in vivo of organisms that it readily inhibits in vitro. The 

 reason for this is that in most instances pantoyltaurine is itself antag- 

 onised by the relatively large amounts of pantothenic acid present in 

 the blood of the host, and there is then insufficient " free " pantoyl- 

 taurine left over to inhibit the growth of the invading organism. 



Only by selecting a test animal which had a relatively low concen- 

 tration of pantothenic acid in the blood was a therapeutic effect 

 observed, and it was found that, whereas mice infected with a haemo- 

 lytic streptococcus died however much pantoyltaurine was adminis- 

 tered, rats could be protected by giving frequent massive doses of the 

 inhibitor. 21 Under these conditions the ratio of pantoyltaurine to 

 pantothenic acid was kept above the value required for in vitro ac- 

 tivity. When the blood pantothenic acid concentration was artificially 

 increased, however, pantoyltaurine ceased to be effective. 



Since human blood contains a somewhat lower concentration of pan- 

 tothenic acid than rat blood, it is possible that pantoyltaurine might 

 be effective in humans, but the response would not be likely to be 

 dramatic and the dose would have to be very large. Pantoyltaurine 

 had no trypanocidal or antimalarial activity in experimental animals. 

 In spite of the fact that pantoyltaurine is of no practical thera- 

 peutic importance, it has been responsible for throwing much new 

 light on chemotherapy and on the phenomenon of drug resistance, 

 and probably more is known about the mode of action of pantoyl- 

 taurine than of any other chemotherapeutic substance, thanks mainly 

 to the work of H. Mcllwain. 



382 



