Follitropin beta is a recombinant FSH. It is produced by recombinant DNA technology, using a Chinese hamster ovary cell line transfected with the human FSH subunit genes. The primary amino acid sequence is identical to that of natural human FSH. Small differences in the carbohydrate chain structure are known to exist.
FSH is indispensable in normal follicular growth and maturation, and gonadal steroid production. In the female the level of FSH is critical for the onset and duration of follicular development, and consequently for the timing and number of follicles reaching maturity. Follitropin beta can thus be used to stimulate follicular development and steroid production in selected cases of disturbed gonadal function. Furthermore follitropin beta can be used to promote multiple follicular development in medically assisted reproduction programs [e.g. in vitro fertilisation/embryo transfer (IVF/ET), gamete intrafallopian transfer (GIFT) and intracytoplasmic sperm injection (ICSI)]. Treatment with follitropin beta is generally followed by administration of hCG to induce the final phase of follicle maturation, resumption of meiosis and rupture of the follicle.
After intramuscular or subcutaneous administration of follitropin beta, maximum concentrations of FSH are reached within about 12 hours. After intramuscular administration of follitropin beta, the maximum FSH concentrations are higher and reached earlier in men as compared to women. Due to the sustained release from the injection site and the elimination half-life of about 40 hours (ranging from 12 to 70 hours), FSH levels remain increased for 24-48 hours. Due to the relatively long elimination half-life, repeated administration of the same dose will lead to plasma concentrations of FSH that are approximately 1.5-2.5 times higher than after single-dose administration. This increase enables therapeutic FSH concentrations to be reached. There are no significant pharmacokinetic differences between intramuscular and subcutaneous administration of follitropin beta. Both have an absolute bioavailability of approximately 77%.
Recombinant FSH is biochemically very similar to urinary human FSH and is distributed, metabolised, and excreted in the same way.
Single-dose administration of follitropin beta to rats induced no toxicologically significant effects. In repeated-dose studies in rats (two weeks) and dogs (13 weeks) up to 100-fold the maximal human dose, follitropin beta induced no toxicologically significant effects. Follitropin beta showed no mutagenic potential in the Ames test and in the in vitro chromosome aberration test with human lymphocytes.
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