Toxicology: What Are the Side Effects?
This is perhaps the most obvious stage of preclinical development — determining if the drug has unwanted side effects that will preclude development. Typically, a developer will do some toxicology studies early on during the optimization stage to see if the drug has a reasonable safety profile. There’s no point in bringing forward an unsafe candidate.
More formal toxicology is done later on with the final drug substance that will be used in clinical trials, in case there are toxic effects of the drug when combined with other ingredients in the formulation.
During toxicology studies, developers look at many different doses. Typically, they will attempt to find an upper dose that is toxic, to know how far they can push the dose in people (which will be to a level significantly less than the level where they first saw adverse events in animals).
Early versions of these studies inform the company as to what types of delivery are feasible while later studies support the probability that the trial will be safe.
There are standard tests mandated by the FDA that are required for all drugs, as well as more generalized animal studies to look for unexpected signs of toxicity. Developers pay careful attention to any toxicity that might be caused by the drug’s action (e.g., if working with a growth factor that increases the growth of blood vessels, you would be looking for any signs of bleeding).
Toxicology studies that are required before a short phase 1 safety study may be relatively short (e.g., 12-week studies in mice), but the FDA requires longer studies prior to initiation of longer clinical trials, in case toxic effects take a while to become obvious.
Obviously, not all safety issues will show up in animal studies. Sometimes, signs of a side effect may not be recognized until a drug is administered to patients, but toxicology studies are designed to reduce the chances of this happening.
Next: Manufacturing
