The AIDS virus's ability to quickly mutate and become resistant to new drugs makes it difficult for doctors to choose medications that will work. Researchers at Virco Group in Oxford, England, have created a new tool to give doctors better information about viral drug resistance, allowing them to design effective therapies. Called Virtual Phenotype, the analysis takes the genetic code of a patient's HIV strain and predicts the drugs it will be resistant to. The system, one of the earliest examples of pharmacogenomics in action, reportedly provides the first quantitative analysis of viral drug resistance. The analysis is quicker than actual phenotype testing, which involves growing virus and screening it with drugs, and costs up to three times less. Virco is developing similar databases for cancer and hepatitis B.