Abstract: AIM: To evaluate the missed and remedial dosage regimens in cancer patients using erlotinib population pharmacokinetics (PPK) model by Monte Carlo simulation (MCS). METHODS: According to erlotinib PPK model (150 mg po qd), 10 000 MCS were estimated for missed doses and remedial dosage regimens (6 h, 12 h, 18 h, and 24 h double doses) by NONMEM. The proportion of people outside the individual treatment window (ITW) and duration outside the ITW (>5%) under the missed and remedial regimens were calculated, and the rationality of the supplemental regimen in each scenario were analyzed. RESULTS: When missed taking erlotinib, the drug concentration continued to drop to the next medication time and affected the next day's concentration. The durations below the ITW were 25.1 h and 6.6 h, respectively. The proportion of people below ITW increased from 6.82% to 14.55%, and the duration time increased from 5.9 h to 23.6 h; the proportion of people above ITW increased from 5.99% to 10.74%, and the duration time increased from 3.7 h to 9.7 h. CONCLUSION: According to MCS results, patients should improve erlotinib medication compliance and avoid missed doses. In case of missed dose, remedial should be given as soon as possible, but it is not recommended to take remedial or double dosage near the next administration time to avoid increased adverse drug reactions.

Key words: erlotinib, medication adherence, population pharmacokinetics, Monte Carlo simulation