Drug Therapy Gets Personal with Genetic Profiling

Pharmacogenetics Holds Great Promise for Improving Prescribing Practices and Avoiding Adverse Effects

Dana Bartlett, MSN, RN

Disclosures

Am Nurs Journal. 2011;6(5):23-28. 

In This Article

Abstract and Introduction

Abstract

Two patients are admitted to different hospitals for treatment of deep vein thrombosis. One receives warfarin, with the dosage based on her age and weight. The other also is prescribed warfarin, but the treating physician determines the dosage with an algorithm that uses data about the patient's genetic profile and activity of the cytochrome 2C9 enzyme and the VKORC1 enzyme (vitamin K epoxide reductase complex subunit 1); both enzymes metabolize warfarin.
The first patient suffers several bleeding episodes because her coagulation can't be stabilized; she requires a transfusion and is hospitalized for 10 days. The second patient remains free from bleeding episodes and is discharged 3 days later.

Introduction

Like most nurses, you're probably aware that the usual dosage of a drug may turn out to be considerably too high or too low for a particular patient; a drug might prove to be ineffective with a certain patient; or a patient may suffer an unexpected adverse drug effect. Chances are, you also know you can't always predict whether a drug or a particular dosage will turn out to be harmful. Millions of adverse drug reactions occur each year in the United States. A 2002 study found that 10.3% of outpatients had been prescribed a drug with a "black box" warning, indicating the potential for a serious or even fatal adverse reaction.

Many drugs are considered effective only in a certain percentage of the population, estimated by one source at 25% to 60% and by another at 50% to 75% of patients. For the entire range of commonly prescribed drugs, the efficacy rate varies even more. Cyclo-oxygenase 2 (COX-2) inhibitors, such as celecoxib (Celebrex), are about 80% effective for the general population, while oncology drugs are only about 25% effective.

Unpredictability and lack of efficacy aren't limited to new drugs, as the opening scenario illustrates. Warfarin, one of the most common drugs, has been used since the 1950s. Yet it's still notoriously difficult to prescribe and often causes unpredictable effects. What's more, individual dosing requirements for this drug vary greatly among patients.

Of course, many drugs work well for many people. Nonetheless, despite rigorous development and testing, some fail to produce the intended effects in certain individuals, and some can even cause harm.

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