Chapter 1 - Introduction to Therapeutic Drug Monitoring: Frequently and Less Frequently Monitored Drugs

Abstract

Therapeutic drug monitoring is useful for individual dosage adjustment and avoiding drug toxicity for certain drugs with a narrow therapeutic window. However, only relatively few drugs require therapeutic drug monitoring and most of these drugs are used for treating a chronic condition. The exceptions are vancomycin and aminoglycosides, which are used for a relatively short time for treating a life-threatening infection. These drugs require therapeutic drug monitoring due to their high threshold of toxicity. In general approximately 26 drugs are routinely monitored in clinical laboratories, and for most of these drugs there are readily available immunoassays which can be adopted on automated analyzers. These drugs include cardioactive drugs, anticonvulsants, anti-asthmatics, tricyclic antidepressants, immunosuppressants, certain antibiotics and certain anticancer drugs – most commonly, methotrexate. There are approximately 25–30 drugs that are monitored less frequently, and for most of these drugs immunoassays are not commercially available. Therefore, chromatographic methods are usually employed for their determination in serum, plasma or whole blood. These drugs include certain newer anticonvulsants (such as lamotrigine and gabapentin), certain cardioactive drugs (for example, flecainide, tocainide, etc.), several anticancer drugs, and few antidepressants of the SSRI (selective serotonin reuptake inhibitor) class (for example, fluoxetine, paroxetine, and sertraline).