Pharmacodynamic Models: Additive and Proportional Drug Effect Model

Drug response models describe how pharmacological agents interact with biological systems to produce measurable effects. Baseline responses are inherent physiological activities without a drug significantly influencing the observed pharmacological outcomes. Depending on the drug response model employed, these baseline responses may combine with the drug's effect in either an additive or proportional manner.

Additive Drug Response Model

In the additive model, the drug effect is independent of the baseline response. This implies that the observed effect, E, is the sum of the baseline response and the drug's pharmacological action. The relationship between drug concentration and effect can follow a linear pattern, where E increases proportionally with concentration or is characterized by a sigmoidal curve. Plasma concentration–response plots for stimulatory responses in this model display an increasing trend as the drug concentration rises.

Proportional Drug Response Model

The proportional model considers the drug effect as a multiple of the baseline response. The drug may amplify or diminish the baseline activity, creating stimulatory or inhibitory effects. This model also accommodates linear or E_max-type relationships. In this scenario, a higher baseline leads to more significant absolute changes in effect. Conversely, inhibitory effects reduce the baseline response fractionally. The concentration-response graph for proportional models illustrates how a higher baseline accentuates the observable drug effect, aligning with physiological expectations.

By modeling baseline responses and drug effects, these frameworks are essential for understanding drug efficacy and optimizing therapeutic regimens.