Pharmacodynamics HIV Drugs

 Pharmacodynamics is the study of drug concentration and effect relationships. Whereas pharmacokinetics describes what the body does to the drug, pharmacodynamics describes what the drug does to the body. The general relationship between pharmacokinetics and pharmacodynamics is depicted. Several factors are important with respect to pharmacokinetic and pharmacodynamic relationships. First, a given dose of a drug does not always produce the same blood concentration. Although other factors are involved, this variability in blood concentrations is primarily a result of between-patient differences in drug absorption and clearance. Second, variability in blood concentrations leads to variability in concentrations at the site of action. Consequently, variability at the site of action ultimately contributes to heterogeneity in response to therapy. The mean (±SD) of various pharmacokinetic parameters for the HIV-1 protease inhibitors the magnitude of the SDs illustrates the variability observed with each drug following the same dose. Typically, concentration and effect relationships are modeled mathematically. The most common model used is the maximum effect (Emax) model, which is derived from classic drug receptor theory. When drug concentrations from 20% to 80% of the Emax are obtained, the concentration-response relationship may appear to be linear. This relationship may occur because the analytical techniques used to detect low drug concentrations might not be available and high concentrations are avoided to prevent toxicities.