Genetic variations between patients can impact the efficacy of a drug. In the case of metoprolol, variations of alleles in the beta-1-adrenergic receptor can result in a very effective response, or no response at all. This is due to alterations in the structure of the receptor, impairing the binding of the drug molecule and thus making it ineffective in some patients.
Clinical genomics can be used to identify patients with specific mutations that make a drug highly effective or ineffective, supporting clinicians in making decisions. This is a form of personalised medicine, allowing quantitative decisions to be made on care pathways.