indication

For the treatment of patients with thrombocythemia, secondary to myeloproliferative disorders, to reduce the elevated platelet count and the risk of thrombosis and to ameliorate associated symptoms including thrombo-hemorrhagic events.

pharmacology

Anagrelide is a drug used for the treatment of essential thrombocytosis (ET; essential thrombocythemia). It works by inhibiting the maturation of megakaryocytes into platelets. The exact mechanism of action is unclear, although it is known to be a potent (IC50 = 36nM) inhibitor of phosphodiesterase-III.

mechanism of action

The mechanism by which anagrelide reduces blood platelet count is still under investigation. Studies in patients support a hypothesis of dose-related reduction in platelet production resulting from a decrease in megakaryocyte hypermaturation. In blood withdrawn from normal volunteers treated with anagrelide, a disruption was found in the postmitotic phase of megakaryocyte development and a reduction in megakaryocyte size and ploidy. At therapeutic doses, anagrelide does not produce significant changes in white cell counts or coagulation parameters, and may have a small, but clinically insignificant effect on red cell parameters. Anagrelide inhibits cyclic AMP phosphodiesterase III (PDEIII). PDEIII inhibitors can also inhibit platelet aggregation. However, significant inhibition of platelet aggregation is observed only at doses of anagrelide higher than those required to reduce platelet count.

toxicity

There are no reports of overdosage with anagrelide, however thrombocytopenia, which can potentially cause bleeding, is expected from overdosage. Single oral doses of anagrelide at 2,500, 1,500 and 200 mg/kg in mice, rats and monkeys, respectively, were not lethal. Symptoms of acute toxicity were: decreased motor activity in mice and rats and softened stools and decreased appetite in monkeys.

biotransformation

Extensive, with < 1% recovered unchanged in the urine. Metabolized primarily in the liver by cytochrome P450 1A2 (CYP1A2). Recently, it was found that anagrelide is bio-transformed in humans into two major metabolites (6,7-dichloro-3-hydroxy-1,5 dihydro-imidazo[2,1-b]quinazolin-2-one (BCH24426) and 2-amino-5,6-dichloro-3,4,-dihydroquinazoline (RL603). Whether these metabolites have biological activities that may underlie the mode of action of the parent drug is presently unclear.

half life

At fasting and at a dose of 0.5 mg of anagrelide, the plasma half-life is 1.3 hours.

drug interactions

Ginkgo biloba: Additive anticoagulant/antiplatelet effects may increase bleed risk. Concomitant therapy should be avoided.

Treprostinil: The prostacyclin analogue, Treprostinil, increases the risk of bleeding when combined with the antiplatelet agent, Anagrelide. Monitor for increased bleeding during concomitant thearpy.