Pharmacologic monitoring and determinants of intracytoplasmic drug levels

Imatinib (IM) is the gold standard for the treatment of chronic myeloid leukaemia (CML). However, there exists significant interpatient variability in plasma exposure for a given dose of the drug. Several recent studies have revealed a correlation between imatinib trough plasma levels and clinical response, suggesting that measurement of plasma levels could be a useful tool to optimise IM dose. Despite this apparent link, many important questions on the use of IM blood level testing remain unanswered. We recommend IM dosing for patients (1) who are not responding to IM as well as expected, (2) who are suspected to be poorly compliant to their IM regimen, (3) who experience adverse events that are unusually severe for the prescribed dosage and (4) when a drug–drug interaction is suspected.