Anator Mechanism of Action

Pharmacology: Mechanism of action: The precise mechanism by which anagrelide reduces blood platelet count is unknown. In cell culture studies, anagrelide suppressed expression of transcription factors including GATA-1 and FOG-1 required for megakaryocytopoiesis, ultimately leading to reduced platelet production.
In vitro studies of human megakaryocytopoiesis established that anagrelide's inhibitory actions on platelet formation in man are mediated via retardation of maturation of megakaryocytes, and reducing their size and ploidy. Evidence of similar in vivo actions was observed in bone marrow biopsy samples from treated patients.
Anagrelide is an inhibitor of cyclic AMP phosphodiesterase III.
Pharmacokinetics: Absorption: Following oral administration of anagrelide in man, at least 70% is absorbed from the gastrointestinal tract. In fasted subjects, peak plasma levels occur about 1 hour after administration. Pharmacokinetic data from healthy subjects established that food decreases the Cmax of anagrelide by 14%, but increases the AUC by 20%. Food also decreased the Cmax of the active metabolite, 3-hydroxy-anagrelide, by 29%, although it had no effect on the AUC.
Biotransformation: Anagrelide is primarily metabolised by CYP1A2 to form, 3-hydroxy anagrelide, which is further metabolised via CYP1A2 to the inactive metabolite, 2-amino-5, 6-dichloro-3, 4-dihydroquinazoline.
Elimination: The plasma half-life of anagrelide is short, approximately 1.3 hours and as expected from its half-life, there is no evidence for anagrelide accumulation in the plasma. Less than 1% is recovered in the urine as anagrelide. The mean recovery of 2-amino-5, 6-dichloro-3, 4-dihydroquinazoline in urine is approximately 18-35% of the administered dose. Additionally, these results show no evidence of auto-induction of the anagrelide clearance.
Linearity: Dose proportionality has been found in the dose range 0.5 mg to 2 mg.
Paediatric population: Pharmacokinetic data from exposed fasting children and adolescents (age range 7-16 years) with essential thrombocythemia indicate that dose normalised exposure, Cmax and AUC, of anagrelide tended to be higher in children/adolescents compared with adults. There was also a trend to higher dose-normalised exposure to the active metabolite.
Elderly: Pharmacokinetic data from fasting elderly patients with ET (age range 65-75 years) compared to fasting adult patients (age range 22-50 years) indicate that the Cmax and AUC of anagrelide were 36% and 61% higher respectively in elderly patients, but that the Cmax and AUC of the active metabolite, 3-hydroxy anagrelide, were 42% and 37% lower respectively in the elderly patients. These differences were likely to be caused by lower pre-systemic metabolism of anagrelide to 3-hydroxy anagrelide in the elderly patients.