A method is described for effecting computer-implemented decision-support in the selection of a drug therapy of patients having a viral disease. A rules database is provided and patient data is entered including genotype data on the viral genome of the viral disease. The rules database comprises a number of associated rules for each available drug for treatment of the viral disease. Each rule indicates the suitability of the drug for treatment of a specific viral genotype. The patient data is entered into the rules database, the database providing an output of drugs suitable for therapy. The drugs suitable for therapy are displayed in a ranking in accordance with their suitability indication, for selection.