CHEMOTHERAPY 



127 



NH.CO. 



CH. 



cn. 



SOgNa 



I 



I 

 CO 



CO.NH 



I SOgNa 



NH 



>C0 



NH.CO.NH 



SO,Na 



SOgNa 



which is effective against natural trypanosome infections 

 by T. gambiense and T. rhodesiense, but still ineffective 

 in the later stages of the disease. This, but not the other 

 disadvantages, was overcome by the use of tryparsamide, 



OH 



CONH2.CH2NH 



>As = o , and similar drugs such 



ONa 



as arsanine and neocryl containing pentavalent arsenic. 



Atoxyl was shown to be effective also against the 

 spirochsete causing syphilis. Even more effective is 

 salvarsan or arsphenamine, 



H0< 



'^^ . It was later shown that 



\ 



NH2.HCI NH2.HCI 



these substances were not themselves active 

 in vitro but that they were converted in the body, by 

 reduction and partial oxidation respectively, to deriva- 

 tives of phenyl-arsenoxide, <^ />-^sO, which were 



highly lethal in vitro to spirochaetes and trjrpanosomes . 

 The therapeutic use of phenylarsenoxide derivatives in 

 the ordinary way is not possible since they are excreted 

 too rapidly to be effective unless given in doses which 

 would be too toxic to the host. The arsenoxide derivative 



mapharsen, or mapharside. 



H0< 



>As0 



I 

 NH.HCl 



is used, 



however, by the slow intravenous drip method to give a 

 short but intensive treatment for syphilis. 



