HMG is the longest-used preparation, having been developed as a replacement for pregnant mare serum gonadotropins (PMSG) extracted from pregnant horses, used for their FSH effect biologically effective for ovarian stimulation in women. The HMG products Pergonal® and Neopergonal®, both from Serono, Inc., and Humegon® by Organon Co., are all characterized by having a 1:1 ratio of FSH to LH. A second generation of highly purified gonadotropin extract (HP-HMG, (Menogon® or Menopur®)), was introduced later as an improvement due to several additional purification steps. The LH effect is claimed to be partly related to the pituitary hCG present in the urine, and is important to balance the relative shortage of LH in the post-menopausal urine. The existence of hCG secretion by the pituitary is still a matter of debate, and in any case it probably constitutes less than 1 % of the total LH bioactivity of menotropins preparations [Fostimon EU MRP registration, Personal communication to author].

Urinary FSH (uFSH) first appeared in 1988 as an attempt to eliminate all LH activity that was considered by some to be deleterious for treatment of polycystic ovarian disease (PCOD). To this end FSH was initially concentrated from human post-menopausal urine by using monoclonal antibodies to bind and remove LH. However, this biologically pure FSH (called urofollitropin, trade names Fertilin® and Metrodin®) was still contaminated by various other urinary proteins. By 1995, FSH was directly isolated from the urine through the use of its own monoclonal antibodies; this highly purified hormone (called uFSH-HP) contained less than 0.1 % LH and less than 5 % of other protein contaminants. In addition, the process enhanced the original hormone concentration of 100–150 IU/mg protein of uFSH to 10,000 IU/mg for uFSH-HP (originally Metrodin HP®, presently marketed as Fostimon® and Bravelle®) [2]. More highly purified FSH contains a higher proportion of the more acidic isoforms, due to characteristics of pituitary FSH secreted after the menopause, and also because less acidic glycoforms are more prone to hepatic metabolism: affinity of the various isoforms for hepatic asialo-glycoprotein receptors is diminished in proportion to their sialic acid contents.

Aside from the varied LH content in HMG preparations, there are other contrasts between the available FSH extracts: for example, HMG and uFSH-HP (Bravelle®), both manufactured by Ferring Corp, contain lesser amounts of acidic isoforms than does the uFSH-HP (Fostimon®) sold by IBSA, SA, because the purification process for the former product was not initially designed to protect the sugar residues of FSH. Purification procedures for Fostimon® are able to isolate and preserve glycosylated forms at certain critical steps in the extraction process. This secures a more acidic and more complete mix of FSH isoforms in the final product [Fostimon EU MRP registration, Personal communication to author]. Of the four FSH preparations now available, Fostimon® has the most complete isoform profile and the highest proportion of acidic isohormones.

Recombinant FSH is manufactured by a genetic engineering process utilizing cells from the Chinese hamster ovary (CHO). These cells are uniquely able to link the two synthesized heterodimers with glycosylation. rFSH introduction in 1997 eliminated the burden of post-menopausal urine collections, and it provided a highly stable injectable solution designed for patient self-administration with a convenient subcutaneous injection pen that also reduces wastage.

In contrast to an rFSH produced in human embryonic kidney (HEK-293) cell lines, the CHO gonadotropin contains less acidic isoform than its extracted counterparts because the process of glycosylation is somewhat less effective in CHO cells than in pituitary gonadotrophs. As a result, commercial rFSH contains less complex carbohydrate, a higher proportion of simple oligosaccharides, no bisecting residue branching, and a tri-sialylated FSH form not found in natural human FSH [3, 4]. Further, because the glycosylation and the purification procedures are somewhat different, the two rFSH products (follitropin alpha, Gonal F® and follitropin beta, Puregon®) demonstrate distinct isoform profiles. Because follitropin alpha is more acidic [5], its half-life after multiple subcutaneous injections is longer than for follitropin beta (36 h vs 24 h) [6].

Four gonadotropin preparations with FSH effect are actually available for clinical use (Table 3.1). Two additional arrivals to the FSH marketplace provide some interesting issues but do not create new FSH isoform profiles.

The combination of follitropin alpha with lutropin alpha (Pergoveris®), available since 2007, modernizes the HMG concept with a 2/1 ratio of FSH/LH. However the FSH isoform profile remains similar to that of follitropin alpha. The 2/1 FSH/LH ratio seems to be especially useful for treatment of hypogonadotropic hypogonadism as well as for multifollicular stimulation. Nevertheless, its FSH isoform profile remains the same as Gonal F®.

A long acting rFSH (corifollitropin alpha, Elonva®), which combines the beta subunit of follitropin beta with the bulky carboxyl terminal peptide of the beta hCG subunit, has a prolonged presence in plasma as a result of its reduced hepatic and renal elimination. The plasma half-life of this “hybrid FSH” is two to three times longer than that of the usual rFSH, but its isoform profile remains nevertheless the same as for follitropin beta. Following an injection of corifollitropin alpha, the maximal concentration of FSH activity is reached within 2 days, instead of the 4–5 days necessary to obtain the equilibrium concentration with daily injections of rFSH (Fig. 3.1) [7]. Maximum plasma levels are dose-related, and contrasts with the duration of its effect, which remains unaltered at all doses. A single administration of corifollitropin alpha is effective over 7 days, which reduces the number of injections and improves patient comfort. A single dose of corifollitropin alpha has been shown to have an equal efficacy to daily doses of 200 IU of follitropin beta in normo-responders. On the other hand, the FSH dosage cannot be altered during the single administration period, which makes the ovarian stimulation, and particularly classical stimulations, more challenging [8]. For this reason, use of this long acting FSH product is presently restricted to the initial stimulation phase of an antagonist fixed protocol in the multifollicular stimulation for IVF purposes. Pregnancy rates are comparable to those following the use of daily injections of rFSH [9].

A third rFSH (FE 999049) is being tested by Ferring Pharmaceuticals. Unlike the two others, this recombinant gonadotropin is expressed from a cell line of human fetal retinal origin instead of Chinese hamster ovaries [10].