1- Good correlation exists between theophylline bronchodilation effect measured by the pulmonary function test and theophylline plasma conc.
2 - Good correlation exists between warfarin plasma conc and its pharmacological effect measures by the prothrombin time.
3 - Salicylate plasma conc is correlated with its therapeutic and toxic effects. The antipyretic and analgesic effects are observed when salicylate plasma conc is in the range of 100 ug/ml, while salicylate anti-inflammatory effect requires conc in the range of 200-300 ug/ml. Salicylate plasma conc higher than 500 ug/ml results in toxicity.
There are many other examples
The increase in drug conc increases the intensity of drug effect. This may suggest that larger doses should produce better effect. Higher doses may produce more intense effect and also cause adverse effects and toxicity. The goal of drug therapy should be to achieve plasma drug conc that produces the desired therapeutic effect with minimum adverse effects.
