Abarelix

Abarelix is an intramuscularly injectable drug from the group of GnRH antagonists. Abarelix is used to treat advanced or metastasized hormone-dependent prostate cancer.

Abarelix acts via competitive inhibition of the GnRH receptor. This leads to a rapid but reversible interruption of testosterone production. In contrast to treatment with a gonadorelin receptor agonist (see buserelin or triptorelin below), Abarelix does not lead to an initial testosterone flooding, which could possibly trigger an aggravation of the clinical picture.

Clinical studies have shown that testosterone and PSA are lowered more rapidly under Abarelix treatment, both in comparison with treatment with gonadorelin receptor agonists (e.g. goserelin, buserelin) and in comparison with maximum androgen blockade (gonadorelin receptor agonists + antiandrogen). The LH concentration decreases within eight to 24 hours by 51 to 84%, the FSH concentration by about 30%.

Effects on testosterone levels: under therapy with Abarelix, testosterone levels fall to castration levels within a week (in one third of patients after three days). Under a combination of LHRH agonists and antiandrogens, comparable results were achieved only after 21 days.

Abarelix can trigger anaphylactoid reactions (in clinical studies in 1.1% of all treated patients). For this reason it is necessary to observe the patient for at least 30 minutes after the injection.

The side effects of Abarelix are those of hormone withdrawal. These include hot flushes, impotence, sleep disturbances, reduction of sexual drive, depression as well as weakness, weakness, swelling of the mammary glands and hot flushes. In addition, peripheral oedema, pain, dizziness, headaches, sensitivity disorders and gastrointestinal disturbances were frequent.

Important: Prolongation of the QT interval with the risk of QT syndrome.

Plenaxis® was approved in the USA in 2003 and in Germany in 2005.

1. Debruyne F et al (2006) Abarelix for injectable suspension: first-in-class gonadotropin-releasing hormone antagonist for prostate cancer. Future Oncol 2:677-696.
2. Mongiat-Artus P et al (2004) Abarelix: the first gonadotrophin-releasing hormone antagonist for the treatment of prostate cancer. Expert Opinion Pharmacother 5:2171-2179.
3. Kirby RS et al (2009) Abarelix and other gonadotrophin-releasing hormone antagonists in prostate cancer. BJU Int 104:1580-1584.