Determination of telbivudine in the plasma of chronic hepatitis B patients in long‐term treatment by high‐performance liquid chromatographic–tandem mass spectrometry

Creatine kinase elevation is commonly reported in telbivudine‐treated patients. However, little is known about the relationship between this adverse drug reaction and plasma concentration. In this study, a sensitive, rapid and safe quantitative bioanalytical method has been established by using LC‐MS/MS for the determination of telbivudine in a clinical study of chronic hepatitis B patients. The assay was linear in a dynamic 10–10,000 ng/mL range (r 2 > 0.999) and total analysis time was 6 min in this method. The validated method was applied to quantitatively determine plasma concentration in chronic hepatitis B patients during long‐term telbivudine treatment. The results revealed that telbivudine concentration in the creatine kinase‐elevated group (707.92–2788.78 ng/mL) was significantly higher than those with normal creatine kinase (412.63–1108.32 ng/mL). This method was adapted for therapeutic drug monitoring.