Category: Key Principles of Pharmacology

Pharmacodynamics (PD) is the study of the effect of a medicine on the body.  There are two ways a medicine can affect the body:  A medicine can change conditions within the body, or  A medicine can interact with specific parts of the body on a cellular or sub-cellular level.  The primary objective of pharmacodynamic studies is to…

Birkett (2009) describes bioequivalence as “a clinical definition referring to two formulations of a drug”.   “Drugs are considered bioequivalent if the extents and rates of absorption of drug from them are so similar that there is likely no clinically important difference between their effects”  The EMA states “Two medicinal products containing the same active substance are considered bioequivalent if…

In order to understand and interpret pharmacokinetik measurements the concept of bioavailabity should be known. To note: Absorption and bioavailability are related concepts.  In Pharmacokinetics Made Easy (Birkett, 2009) defines bioavailability as:  “Bioavailability is the fraction of the dose which reaches systemic circulation as intact drug”    Other definitions are possible and perhaps even desirable. The flaw of most definitions is the tendency to ignore the…

Based on data gathered during pharmacokinetic studies, Pharmacokinetics (PK), applying scientific and mathematical models helps to predict and understand the time course of Absorption, Distribution, Metabolism, and Excretion of medicines in the body.. This allows scientists to assess the relationship between the medicine’s beneficial and toxic effects, and to predict the safety and tolerability of the medicine in humans. Data gathered during pharmacokinetic studies…

It refers to how the body gets rid of a medicine or its metabolites. There are three main routes of elimination: kidneys (urine), liver, and bowel (bile in faeces). Most medicines are excreted as active, partially active, or inactive metabolites by the kidneys. Infants and elderly have underdeveloped or impaired abilities to metabolise and excrete…

Metabolism is the conversion of one chemical compound into another. Most metabolism of medicines occurs in the liver in the ‘first-pass effect’, although some processes occur in the gut wall, lungs and blood plasma. On the whole, as medicines are metabolised their therapeutic effect changes. Substances (medicines, toxins, foods, etc.) absorbed into the bloodstream from the stomach and…

It refers to how medicines are distributed throughout the body and reach their intended target. The degree of distribution depends on the medicine’s physical and chemical properties as well as its ability to penetrate cell membranes and blood vessels. For example, not all the medicines can have an effect on the brain because only fat-soluble…

Absorption refers to how medicines enter the bloodstream. A few of the most common ways to administer medicines are: Oral administration (PO: per os – by mouth) is a route where a substance (e.g. tablet, syrup) is taken through the mouth to be absorbed from the stomach or intestine, enters the liver and the general circulation. This…

Pharmacokinetics (PK) is the study of the effect the body has on a medicine. In other words, pharmacokinetics studies four major mechanisms usually identified in many text books with the acronym ADME: Absorption: How the medicine gets into the body Distribution: Where the medicine goes in the body Metabolism: How the body chemically modifies the medicine Excretion: How…