An Introduction to Blood Level Testing
Blood level testing, or therapeutic drug monitoring (TDM), involves measuring a drug's concentration in a patient's blood and then using that information to individualize the drug's dosage or schedule for that patient.1
Therapeutic drug monitoring is used to:
- Maximize a drug's therapeutic effect1
- Minimize toxicity1
- Assess patient adherence2
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Therapeutic drug monitoring is generally employed with drugs that:
- Exhibit considerable intra- or interpatient variability1
- Have an established relationship between concentration and pharmacological effects1
- Lack a wide therapeutic index1
- Can be measured with a precise, accurate drug assay1
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The Expanding Role of Blood Level Testing in Oncology
Over the past 15 years, therapeutic drug monitoring has begun to play a greater role in oncology.1,3 A key reason for this is the availability of a growing number of oral anticancer agents. It is estimated that up to 30% of new oncology drugs are being developed as oral formulations— this percentage of anticancer agents is expected to substantially increase in the near future.4
Therapeutic drug monitoring is critical for oral oncology drugs, because oral agents are inherently more susceptible than IV agents to intra- and interpatient variability in absorption, bioavailability, and adherence.3,4 Subtherapeutic drug concentrations have been identified as the most important concern relating to the oral administration of anticancer agents.4
Therapeutic drug monitoring is currently used to optimize therapy with oral anticancer agents such as methotrexate and mercaptopurine;1,3 however, its use with tyrosine kinase inhibitors has only recently begun to be established.5,6
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