Pharmacodynamics Concepts

Pharmacodynamics (PD) is the study of the biochemical and physiologic effects of drugs or pharmaceutical drugs. The effects can include those manifested within animals (including humans), microorganisms, or combinations of organisms.

Pharmacodynamics is the study of a drug's molecular, biochemical, and physiologic effects or actions. It comes from the Greek words "pharmakon" meaning "drug" and "dynamikos" meaning "power." All drugs produce their effects by interacting with biological structures or targets at the molecular level to induce a change in how the target molecule functions in regards to subsequent intermolecular interactions. These interactions include receptor binding, post-receptor effects, and chemical interactions. Examples of these types of interactions include (1) drugs binding to an active site of an enzyme, (2) drugs that interact with cell surface signaling proteins to disrupt downstream signaling, and (3) drugs that act by binding molecules like tumor necrosis factor (TNF).

Pharmacodynamics.

Emax is the maximal effect of a drug on a parameter that is measured. For example, this could be a measure of platelet inhibition as an ex-vivo test or the maximum lowering of blood pressure

EC50 is the concentration of the drug at a steady-state that produces half of the maximum effect

Hill coefficient is the slope of the relationship between drug concentration and drug effect. Hill coefficients above 2 indicate a steep relationship (i.e., small changes in concentration produce large changes in effect), and hill coefficients above 3 indicate an almost instantaneous "all or none" effect.

Pharmacodynamics factors

Pharmacodynamics is the study of the relationship between the concentration of drug at the site of action and the biochemical and physiological effect. The response of the receptor may be affected by the presence of drugs competing for the same receptor, the functional state of the receptor or pathophysiological factors such as hypokalaemia. Interindividual variability in pharmacodynamics may be genetic or reflect the development of tolerance to the drug with continued exposure. High pharmacodynamic variability severely limits the usefulness of monitoring drug concentrations as they are likely to give a poor indication of the effectiveness of therapy.

Pharmacodynamics Parameters

Pharmacodynamics is the study of the biochemical and physiological effects of drugs and their mechanisms of action. Pharmacodynamic parameters relate the pharmacokinetic factors to the ability of an antimicrobial to kill or inhibit the growth of the infecting organism. Pharmacodynamic parameters include the following3:

Time for which the serum concentration of a drug remains above the minimum inhibitory concentration (MIC) for a dosing period (T > MIC)

• Ratio of the maximum (peak) antimicrobial concentration, Cmax, to MIC (Cmax/MIC)

• Ratio of the AUC during a 24-hour period to MIC (AUC24/MIC)

• Postantibiotic effect (PAE)

Pharmacodynamically, the rate and extent of the bactericidal activity of an antimicrobial agent are dependent on the interaction between and among drug concentration at the site of infection, bacterial load, phase of bacterial growth, and the MIC for the pathogen.11 It follows that a change in any of these factors will alter the activity of the antimicrobial agent against a particolar pathogen and may affect the outcome of therapy.

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With kind regards,

Nancy Ella

Editorial Manager

Journal of Pharmaceutical Care & Health Systems