Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1 Pharmacodynamic properties
Pharmacotherapeutic group: Other antineoplastic agents, ATC code: L01XX23.

Mechanism of action
Mitotane is an adrenal cytotoxic active substance, although it can apparently also cause adrenal inhibition without cellular destruction. Its biochemical mechanism of action is unknown. Available data suggest that mitotane modifies the peripheral metabolism of steroids and that it also directly suppresses the adrenal cortex. The administration of mitotane alters the extra-adrenal metabolism of cortisol in humans, leading to a reduction in measurable 17- hydroxy corticosteroids, even though plasma levels of corticosteroids do not fall. Mitotane apparently causes increased formation of 6-beta-hydroxy cholesterol.

Clinical efficacy and safety
Mitotane has not been studied in a comprehensive clinical development program. Available clinical information comes mainly from published data in patients with inoperable or metastatic adrenal carcinoma. In terms of overall survival, four studies conclude that mitotane treatment does not increase the survival rate whereas five find an increase in the survival rate.
Among the latter, three studies find such an increase only in patients in whom mitotane plasma is above 14 mg/L.

Mitotane plasma levels and the possible relationship with its efficacy were studied in the FIRM ACT trial, a randomized, prospective, controlled, open–label, multicenter, parallel- group study to compare the efficacy of etoposide, doxorubicin and cisplatin plus mitotane (EDP/M) to that of streptozotocin plus mitotane (Sz/M) as first-line treatment in 304 patients.
The analysis of patients who achieved mitotane levels ≥ 14 mg/L at least once in 6 six months versus patients who mitotane levels were < 14 mg/L could suggest that patients with mitotane plasma levels ≥ 14 mg/L could have an improvement in disease control rate (62.9% versus 33.5%; p< 0. 0001). However, this result should be cautiously taken since the examination of the mitotane effects was not the primary endpoint of the study.

In addition, mitotane induces a state of adrenal insufficiency which leads to the disappearance of Cushing syndrome in patients with secreting adrenal carcinoma and necessitates substitution hormonotherapy.

Paediatric population
Clinical information comes mainly from a prospective trial (n= 24 patients) in children and adolescents aged at diagnosis from 5 months to 16 years (median age: 4 years) who had an unresectable primary tumour or who presented a tumour recurrence or a metastasic disease; most of the children (75%) presented with endocrine symptoms. Mitotane was given alone or combined with chemotherapy with various agents. Overall, the disease-free interval was 7 months (2 to 16 months). There were recurrences in 40% of children; the survival rate at 5 years was 49%.

Pharmacokinetic Properties

5.2 Pharmacokinetic properties

Absorption
In a study performed in 8 patients with adrenal carcinoma treated with 2 to 3 g daily of mitotane, a highly significant correlation was found between plasma mitotane concentration and the total mitotane dose. The target plasma mitotane concentration (14 mg/L) was reached in all patients within 3 to 5 months and the total mitotane dose ranged between 283 and 387 g (median value: 363 g). The threshold of 20 mg/L was reached for cumulative amounts of mitotane of approximately 500 g. In another study, 3 patients with adrenal carcinoma received Lysodren according to a precise protocol allowing fast introduction of a high dose if the product was well tolerated: 3 g (as 3 intakes) on day 1, 4.5 g on day 2, 6 g on day 3, 7.5 g on day 4 and 9 g on day 5. This dose of Lysodren was continued or decreased in function of side effects and plasma mitotane levels. There was a positive linear correlation between the cumulative dose of Lysodren and the plasma levels of mitotane. In two of the 3 patients, plasma levels of more than 14 mg/L were achieved within 15 days and in one of them levels above 20 mg/L were achieved within approximately 30 days. In addition, in both studies, in some patients, the plasma mitotane levels continued to rise despite maintenance or a decrease of the daily dose of mitotane.

Distribution
Autopsy data from patients show that mitotane is found in most tissues of the body, with fat as the primary site of storage.

Biotransformation
Metabolism studies in man have identified the corresponding acid, 1,1-(o,p'-dichlorodiphenyl) acetic acid (o,p’-DDA), as the major circulating metabolite, together with smaller quantities of the 1,1-(o,p'-dichlorodiphenyl)-2,2 dichloroethene (o,p’-DDE) analogue of mitotane. No unchanged mitotane has been found in bile or in urine, where o,p’-DDA predominates, together with several of its hydroxylated metabolites. For induction with cytochrome P450, see section 4.5.

Elimination
After intravenous administration, 25% of the dose was excreted as metabolites within 24 hours. Following discontinuation of mitotane treatment, it is slowly released from storage sites in fat, leading to reported terminal plasma half-lives ranging from 18 to 159 days.