



OPENING REMARKS 



Sir Charles Harington 



In spite of the great advances that have been made in 

 recent years in the chemotherapeutic treatment of infectious 

 diseases — advances that have brought under some measure 

 of control the majority of protozoal and bacterial infections 

 and some helminthic infections — the subject of chemotherapy 

 remains distressingly empirical. The relationship between 

 chemical structure and biological action in this field is still 

 so ill-defined that we have only one significant guiding prin- 

 ciple, based on biological theory, to help us in the search for 

 new synthetic drugs for specific chemotherapeutic purposes. 

 As for antibiotics the attempt to discover new substances of 

 therapeutic value is admittedly based on no scientific prin- 

 ciple at all, but is an operation such as oil prospecting would 

 be with no adequate background of geological information. 



Even when a new synthetic drug is discovered that proves 

 to be of value in the treatment of a particular infection, it is 

 usually impossible to explain the nature of the action of the 

 drug; indeed the type of activity found is not infrequently 

 quite different from that which is being sought, as is shown 

 for instance by the discovery of a valuable antimalarial, pyri- 

 methamine, in the course of a search for folic acid antagonists. 

 Sometimes the drug proves not to have a direct action on the 

 infecting organism at all, although it can suppress or cure the 

 disease which the micro-organism causes ; thus the anti-malarial 

 drug proguanil has no direct lethal effect on plasmodia, 

 but it is metabolized in the body of the host to a substance 

 that has such an effect. Again hetrazan, which is the most 

 effective remedy so far known for filariasis, does not kill the 

 microfilariae directly but so alters them that they become 

 susceptible to attack by the natural defence mechanisms of the 

 host. The most striking example of such indirect chemothera- 

 peutic action is afforded by the high-molecular surface-active 



DRUa RES. 1 



