Personalised medicine uses information about a person's genotype to choose the most effective drug and dose for them. Genetic screening with DNA probes identifies the alleles a person carries.People respond differently to the same drug partly because they have different alleles. For example, many drugs are broken down by enzymes in the liver, and different alleles of the genes for these enzymes produce enzymes that work faster or more slowly. A slow metaboliser given a normal dose may build up a high concentration of the drug and suffer side effects, while a fast metaboliser may break the drug down before it can work.Example: Herceptin. Some breast cancers over-express the gene for a receptor protein called HER2. The drug Herceptin, a monoclonal antibody, binds to HER2 receptors and is effective only against these HER2-positive cancers. Testing the tumour first means that only patients who will benefit are given the drug.Worked example: a drug is normally given at 100 mg per day. Patients with a slow-metaboliser genotype are prescribed 25% of the normal dose.dose = 0.25 × 100 = 25 mg per day Benefits
• treatment is more effective and starts sooner, because no time is wasted on drugs that will not work
• there are fewer harmful side effects
• money is saved by not prescribing ineffective drugs.Issues: genetic testing costs time and money; for many drugs, how alleles affect the response is not yet known; and there are concerns about keeping genetic information private.
• treatment is more effective and starts sooner, because no time is wasted on drugs that will not work
• there are fewer harmful side effects
• money is saved by not prescribing ineffective drugs.Issues: genetic testing costs time and money; for many drugs, how alleles affect the response is not yet known; and there are concerns about keeping genetic information private.