Pharmacodynamics and chemotherapy compared

In pharmacodynamics at least three problems arise which have little or no counterpart in chemotherapy. 

In the first place, pharmacodynamic results are usually required to be reversible. The patient who submits to an anaesthetic does not expect to be deprived of feeling permanently. In chemotherapy, on the other hand, the toxic action is most esteemed when it is most irreversible. 

In the second place, pharmacodynamic drugs are expected to act with a graded response. In proportion to the severity of a spasm or excessive secretion, so should various doses of the remedy exactly neutralize what is morbid without inflicting upon the patient any further loss of function. The reverse of the graded response, namely the all-or-nothing effect so desirable in chemotherapy, must be avoided in pharmacodynamics. 

Fortunately, from time to time some progress has been made in the direction of A.J. Clark s ideal single-cell pharmacology. Thus the intra- and extracellular response of single nerve or muscle cells can be recorded while ionto-phoretic administration of a drug is being made into the extraneuronal environment (del Castillo and Katz, 1957 Katz, 1966). 

From these considerations, it might be concluded that the study of chemotherapy is immeasurably simpler than that of pharmacodynamics. However, those who study chemotherapy have to perform pharmacodynamic work also in order to follow the side effects of their drugs on the host. Even drugs, such as piperazine and penicillin, which have no side effects at all in the average patient, nevertheless need to be studied pharmacodynamically to discover their pattern of distribution in the body, and the origins of their favourable selectivity. 

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