Pharmacodynamic Parameters

Pharmacodynamic Parameters

The various pharmacodynamic parameters are –

1. Minimum Effective Concentration (MEC)

It is defined as the minimum concentration of drug in plasma required to produce the therapeutic effect. It reflects the minimum concentration of drug at the receptor site to elicit the desired pharmacological response. The concentration of drug below MEC is said to be in the sub-therapeutic level.

In case of antibiotics, the term minimum inhibitory concentration (MIC) is used. It describes the minimum concentration of antibiotic in plasma required to kill or inhibit the growth of microorganisms.

2. Maximum Safe Concentration (MSC)

Also called as minimum toxic concentration (MTC), it is the concentration of drug in plasma above which adverse or unwanted effects are precipitated. Concentration of drug above MSC is said to be in the toxic level.

3. Onset of Action

The beginning of pharmacological response is called as onset of action. It occurs when the plasma drug concentration just exceeds the required MEC.

4. Onset Time

It is the time required for the drug to start producing pharmacological response. It corresponds to the time for the plasma concentration to reach MEC after administration of drug.

5. Duration of Action

The time period for which the plasma concentration of drug remains above the MEC level is called as duration of drug action. It is also defined as the difference between onset time and time for the drug to decline back to MEC.

6. Intensity of Action

It is the maximum pharmacological response produced by the peak plasma concentration of drug. It is also called as peak response.

7. Therapeutic Range

The drug concentration between MEC and MSC represents the therapeutic range. It is also known as therapeutic window.

8. Therapeutic Index

The ratio of MSC to MEC is called as therapeutic index. It is also defined as the ratio of dose required to produce toxic or lethal effects to dose required to produce therapeutic effect.