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Imatinib mesylate, a tyrosine kinase inhibitor, exhibits a weak competitive inhibition on paracetamol (acetaminophen) O-glucuronidation with an inhibition constant (Ki) value of 59 μM. However, the clinical significance of the inhibition has not been evaluated. The pharmacokinetics of imatinib have been studied in white patients with chronic myelogenous leukaemia (CML), but not in Korean patients with CML.Imatinib (400 mg once daily) had no clinically relevant effect on the plasma exposure and the pharmacokinetics of paracetamol (1000 mg once daily) in patients with CML.The pharmacokinetic profile of imatinib in Korean patients with CML was similar to that in whites.The major objective of the present study was to investigate the effect of imatinib on the pharmacokinetics of paracetamol in patients with chronic myelogenous leukaemia (CML).Patients (n= 12) received a single oral dose of acetaminophen 1000 mg on day 1 (control). On days 2-8, imatinib 400 mg was administered daily. On day 8 (treatment), another 1000 mg dose of paracetamol was administered 1 h after the morning dose of imatinib 400 mg. Blood and urine samples were collected for bioanalytical analyses.The area under the plasma concentration-time curve (AUC) for paracetamol, paracetamol glucuronide and paracetamol sulphate under control conditions was similar to that after treatment with imatinib; the 90% confidence interval of the log AUC ratio was within 0.8 to 1.25. Urinary excretion of paracetamol, paracetamol glucuronide and paracetamol sulphate was also unaffected by imatinib. The pharmacokinetics of paracetamol and imatinib in Korean patients with CML were similar to previous pharmacokinetic results in white patients with CML. Co-administration of a single dose of paracetamol and multiple doses of imatinib was well tolerated and safety profiles were similar to those of either drug alone.The pharmacokinetics of paracetamol and its major metabolites in the presence of imatinib were similar to those of the control conditions and the combination was well tolerated. These findings suggest that imatinib can be safely administered with paracetamol without dose adjustment of either drug.