Toxicologist Atholl Johnston ensures that medicines are safe, effective, and given in the proper doses. “Toxicologists determine the dose-response relationship for a drug in animals to determine whether it may be toxic in man,” he says.

Atholl works with Research Chemists from the beginning of medicine development. The Research Chemists find several candidate compounds that could be potential new medicines, and one part of Atholl’s job is to test them on cells and weed out candidates that don’t work. “It takes something like ten thousand candidates to get one successful drug to market,” he says.

Before new medicines are tested in humans, toxicologists study their effects in animals and cells. Atholl works with Animal Technologists who take note of changes in the animals’ weight, health and behaviour during a study. At the end of the study, Atholl weighs and measures the animals’ organs to see what effects the experimental medicine has had. Finally, he slices these organs very thinly to examine the animals’ cells under a microscope. This examination of cells is called histology, and it is an important tool to see how the medicines affect cells.

When these toxicology tests are complete, a new medicine may get approval for testing in humans in clinical trials. Atholl may test trial volunteers’ blood samples, or take biopsies (small tissue samples), to understand the effects of the medicine. Atholl will also work with Pharmacokineticists to determine how much of the medicine stays in the body, and for how long.

Atholl has a degree in toxicology, but toxicologists can come from a biological or medical science background. They then work for pharmaceutical companies or contract research organisations, (companies that run research projects for several companies).

The most satisfying part of the job, he says, is “…seeing the finished product, knowing that you participated in a process that ended up with a successful drug on the market.”

Photo of Atholl Johnston, ToxicologistAtholl Johnston, Toxicologist