There are two main categories of ideas chemists can talk about when considering how drugs work: pharmacokinetics and pharmacodynamics.

Today we’re going to focus on the first one, pharmacokinetics. As you can probably guess by breaking down the word, ‘pharmaco’-’kinetics’ describes how drugs move in the body. Some of the overaraching concepts were covered in my previous post, but in this post we’ll dive a bit deeper.

The main concepts related to pharmacokinetics are summarised by the acronym LADME:

• Liberation*
  • Is about the drug “dissolving”. This is the process where the drug goes from its originally consumed form (e.g. a tablet, capsule or liquid) and mixes into (usually) the stomach acid.
  • As you can imagine, if a medication is broken down by the stomach acid before it can get to the place it is going to act, it’s probably not going to work very well. Similarly, if the drug doesn’t dissolve well, it’s unlikely to be able to go through the following steps in this list.
• Absorption
  • Is generally about how the drugs move through or between the cells in the stomach (or elsewhere in the gut) and into the blood stream
• Distribution
  • Is exactly what it sounds like. This is about how the drug is transported from the site it is originally absorbed from, to its destination.
  • A drug’s intended “destination” in the body is usually called the “target” or the “target site”. This really just makes me think of an arrow aiming for the bullseye – but in reality, we can start to appreciate now that this is all just a bit o’ chemistry.
• Metabolism
  • Again, this is a word that’s pretty well in our day to day lingo. In the drug sphere, this really just means how the drug is processed by the body and broken down into its constituent parts.
  • This process often involves “enzymes”. Enzymes are super cool. They’re basically little magic machines inside cells that take one substance and convert it into something else. Generally, enzymes will convert the drug into an “inactive” form which can later be removed by the body. However in the case of some cool medications called prodrugs, the processing done by the enzymes will actually convert it into its active state – which means the drug can then go off and do its thang.
  • This stage is really important in considering how medications might work (or not work) together. That’s right, we’re talking drug interactions. More on that in a later post.
• Excretion
  • Don’t mean to get into gross zone but this is just what it sounds like. This is how drugs leave the body (i.e. via urine or feces).

*Medications which are not given by mouth (i.e. you don’t swallow it) such as injections can bypass this step as they generally don’t go via the stomach, and can get directly absorbed into the blood stream and transported around the body.

The interesting part about these steps that chemistry will dictate how the drug is metabolised and excreted. There are two main organs that are responsible for this – the liver and the kidneys. More on those in the next post.