Drug toxicity mainly results as a byproduct of drug metabolism, in which a drug may be biotransformed by drug metabolizing enzymes to toxic or nontoxic metabolites. A number of protein families such as P450s, UDP-glucuronosyltransferases, sulfotransferases, organic-anion transporters and multidrug resistance proteins are involved in drug metabolizing processes. Changes in the expression level of these enzymes are a key factor responsible for individual variation in drug metabolism. 
Signosis has developed a plate-based array for profiling 20+ Toxicity-regulated genes. By using this assay, researchers are able to compare gene expression in up to three samples on a single microtiter plate.