Measurement of Bioavailability: Pharmacodynamic Methods

Pharmacodynamic methods measure a drug’s direct effect on the physiological process over time.

Two main pharmacodynamic methods are acute pharmacological and therapeutic responses.

The acute pharmacological response method relates the drug’s effects, such as ECG or pupil diameter changes, to its time course in the body.

At least three biological half-life measurements are plotted in the pharmacological effect-time curve, allowing AUC estimation for accurate bioavailability data.

However, drug formulations or drug conversion to active metabolites compromises the correlation between the measured response and the available drug concentration.

Alternatively, in the therapeutic response method, patients with the targeted disease are given drug formulations to observe the clinical response.

Through this approach, comparing two drug dosage forms for relative bioavailability is difficult due to improper response quantitation.

Sometimes, patients are on multiple medications, leading to drug-drug interactions that interfere with bioavailability measurements.