Improving the Prescription of Licensed Drugs

Much attention has been given to the way in which pharmacogenetics might benefit the pharmaceutical industry in the discovery and development of new drugs. However, the technology offers significant advantages to clinicians, healthcare providers, patients, and companies by improving the purchase, prescription, use, marketing, and surveillance of licensed products. This might be achieved in a number of ways.

Extending the Use of Products Restricted by ADRs

A number of approved drugs already have restricted markets as a result of safety problems. For example, the HIV/AIDS drug Abacavir requires very close monitoring for the first few months of its use due to a severe hypersensitivity reaction in approximately 5% of the patients. This places limits on its clinical use. Trials are currently under way to identify the genomic subgroup who are most at risk of this ADR, so that prescreening can be used to exclude them from therapy. Such strategies might be used to extend the uses of drugs with practice and label restrictions and result both in therapy for a great number of patients and in increased product sales.

Preprescription Screening to Identify Patients at Risk of ADRs

One of the most widely publicized applications of pharmacogenetics is the development of "personalized medicine" in which patients are genotyped to enable physicians to give "the right drug to the right person." Attention has been focused particularly on the possibility of preprescription testing to identify patients at greatest risk of genetically based ADRs resulting from the use of a given drug. These patients could either be offered an alternative therapy or be closely monitored, if none exists. A number of laboratories and private companies in the United States already offer thiopurine methyltransferase (TPMT) genotyping to identify patients most at risk of severe adverse reactions as a result of their inability to metabolize the chemotherapy drug 6-mercaptopurine. This type of application of pharmacogenetics is attractive to doctors, patients, and health care providers, as it would lead to safer prescription and reduce the burden posed by serious ADRs.

Postmarketing Surveillance of Approved Drugs

Pharmacogenetics could also be incorporated into improved postmarketing surveillance of medicines. Patients who have suffered an ADR could be genotyped to see whether there was a genetic basis for their response (16). This might lead to the creation of a test to identify people at high risk of rare ADRs. Rather than leading to drug withdrawal, the introduction of this form of pharmacogenetic testing might also enable some products to remain on the market (18) or to be "rescued" after withdrawal (17). However, regulators have indicated that this latter option is unlikely to win much support.

Preprescription Screening to Identify "Good Responders"

In a similar fashion to preprescription patient safety testing, pharmacogenetics could be used to identify those most likely to respond positively to a specific drug. It is already well established that some patients fail to respond to such common prescription medicines as Prozac. Lichter and Kurth (19) claim that testing for nonresponders would be cost-effective for health care providers, as the expense of genotyping would be more than offset by savings from reducing ineffective prescription. In some cases this might lead to an overall reduction in healthcare costs (18). However, the use of pharmacogenetics by purchasers to reduce the overuse of ineffective drugs in groups of nonresponders clearly conflicts with the interests of the pharmaceutical industry as it is predicated on reduced drug sales (18).

Use of Efficacy Data in Drug Marketing

Pharmacogenetic information could also allow doctors to make a more informed choice about the use of one medicine compared with another in the same drug class. This might also provide some pharmaceutical companies with a powerful marketing tool if they could demonstrate that their medicine was more effective in a particular patient group than a rival product. Such a prospect would be particularly attractive to companies whose products are ranked lower in sales.

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