Comparison of Two Mitotane Starting dose Regimens in Patients with Advanced Adrenocortical Carcinoma

• Context:Mitotane is the only approved drug for treatment of adrenocortical carcinoma(ACC). Its pharmacokinetic properties are not fully elucidated and different dosing regimens have never been compared head-to-head.Objective:To investigate the relationship between mitotane dose and plasma concentration comparing two dosing regimens.Design/Setting:Prospective open-label multicenter trial of a predefined duration of twelve weeks.Patients/Interventions:Forty mitotane-naïve patients with metastatic ACC were assigned to a predefined low- or high-dose regimen by the local investigator. Thirty-two could be evaluated in detail.Main Outcome Measure:Difference in median mitotane plasma levels between both treatment groups.Results:Despite a difference in mean cumulative dose (440±142g versus 272±121g), median maximum plasma levels were not significantly different between the two groups (high-dose 14.3mg/L (6.3-29.7,n=20) versus 11.3mg/L (5.5-20.0,n=12), p=0.235). Ten out of twenty patients on the high-dose regimen reached plasma concentrations ≥14mg/L after 46 days (18-81 days) compared to four of twelve patients on the low-dose regimen after 55 days (46-74 days,p=0.286). All patients who reached 14mg/L at 12 weeks displayed a level ≥4.1 mg/L on day 33 (100% sensitivity). There were no significant differences in frequency and severity of adverse events. Among patients not receiving concomitant chemotherapy mitotane exposure was higher in the high-dose group: 1013±494mg.d/L versus 555±168mg.d/L, p=0.080.Conclusions:The high-dose starting regimen did neither result in significantly different mitotane levels nor in a different rate of adverse events, but concomitant chemotherapy influenced these results. Thus, for mitotane monotherapy the high-dose approach is favorable, whereas for combination therapy a lower dose seems reasonable.

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