Pharmacology for Anaesthesia and Intensive Care

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Section IBasic principles

drug alone, then the point A (^12 ,^12 )can be marked, and there is a straight line indi-

cating additivity. If however we need to combine a concentration a/2 of drug A with

only a concentration b/4 of drug B to elicit the same response, the point (^12 ,^14 )can

be marked, which describes a curve that is concave, suggesting synergism between

drugs A and B. Similarly, if we needed a concentration greater than b/2 of drug B the

curve would be convex, indicating some antagonistic interaction between the two

drugs point C (^12 ,^34 )(Figure4.1).