Preclinical

A Preclinical study is the stage before clinical trials where a candidate drug, vaccine, medical device, or diagnostic assay is tested extensively. This involves in vitro (test tube or cell culture) and in vivo (animal model) experiments using various doses of the study agent to gather preliminary data on efficacy, toxicity, and pharmacokinetics. These tests help determine if a drug candidate has scientific merit for further development as an investigational new drug.

Source: Wikipedia

Not to be confused with: Phase 0 trial
Not to be confused with: Phase 1 trial