Clinical trials in all walks of medicine have five phases of clinical trial. For anybody who does not work in the clinical trials industry they can be tricky to understand. This aims to explain the first phase of clinical trials in humans.
The actual first stage that a new drug will go through is called pre-clinical studies which are conducted in vitro (in test tubes) or in vivo (on animal subjects) and these basically test whether the drug is safe, whether it has any major toxicities and whether it is of any use to go further. In trials phraseology they are testing for efficacy or whether it has any effect, toxicity or how much damage it does pharmacokinetics or how it is absorbed, the rate it’s absorbed at, the length of the effect and how it is excreted. These are completely necessary but not what is being covered here.
Phase 0 clinical trials are what is known as ‘first in human’ trials and are designed to speed up the clinical trials process which can in some cases take decades to complete. The aim is to give the participants sub-therapeutic doses of the drug otherwise known as microdosing to a very small number of healthy participants in order to test the pharmacokinetics as explained above and the pharmacodynamics of the drug which is in essense the effect the drug has on the body. The simplistic summary is that pharmacokinetics is what the body does to the drug whilst pharmacodynamics is what the drug does to the body.
Because the dose that is being given is so small it is impossible to test for safety or what effect it has in terms of curing illness as the dose simply isn’t high enough. In fact that is one of the largest differences between Phase 0 trials and any other phase; there is no chance of the participant being helped by the drug. It is a purely exploratory endevour to discover whether the drug doesn’t do what it is intended to do and to avoid the expense of getting to a later stage years down the line only to discover that the drug isn’t actually doing what the researchers had expected.
The other main difference is that Phase 0 is not a required stage in testing a new drug and in some situations it would be completely unhelpful and therefore a waste of time and expense. In those cases the research would start with Phase 1 studies. They tend to include very low numbers of volunteers; usually around the 10 person mark and basically allow drug companies to decide what drugs to go forwards with based on human data rather than the more inconsistant animal date.