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Corifollitropin Alfa (Elonva)

Written by The Peptide Record editorialClinical review not yet completedLast reviewed 16 September 2026Funding No ads, no affiliate links, no vendor payment

Corifollitropin alfa (Elonva) completes this site's gonadotropin cluster alongside follitropin alfa/beta, menotropins, lutropin alfa and choriogonadotropin alfa — a genuinely different piece of engineering rather than another me-too FSH: one injection, fusing FSH to a sugar-heavy peptide tail borrowed from hCG, replaces the first seven daily FSH injections of an IVF stimulation cycle. It's approved and widely used in Europe and dozens of other countries since 2010, but the FDA has never approved it in the US, after rejecting Merck's application in 2014.

On this page
  1. A hybrid molecule, not another recombinant FSH
  2. The ENGAGE trial
  3. Approved across Europe and beyond, but not the US
  4. Current status

In brief

Should you care? Relevant if you're comparing IVF ovarian-stimulation options outside the US, or came from this site's follitropin alfa/beta page wanting the long-acting, once-per-cycle alternative — not an option currently available to US patients.

The short version

  • A genuine hybrid molecule: FSH fused to the carboxy-terminal peptide (CTP) of hCG's beta subunit, extending its circulating half-life enough that one injection sustains follicle growth for about a week.
  • The ENGAGE trial (over 1,500 patients) found a single 150μg dose produced ongoing pregnancy rates statistically similar to seven days of daily recombinant FSH (38.9% vs. 38.1%).
  • Approved in the EU since January 2010 and in more than 75 countries since — but the FDA issued a Complete Response Letter in July 2014, and no US approval has followed.

A hybrid molecule, not another recombinant FSH

This site's follitropin alfa/beta page covers recombinant FSH, which still requires a daily injection through most of an ovarian-stimulation cycle for IVF. Corifollitropin alfa takes a genuinely different engineering approach: it fuses the FSH beta subunit to the carboxy-terminal peptide (CTP) of human chorionic gonadotropin's beta subunit — the same heavily O-glycosylated sugar tail this site's somatrogon page describes being used to extend a growth hormone's half-life. Borrowed here and fused onto FSH instead, that sugar tail slows the hybrid molecule's clearance enough that a single subcutaneous injection sustains follicle-stimulating activity above the threshold needed for the first seven days of a stimulation cycle — replacing what would otherwise be seven consecutive daily injections with one.

The ENGAGE trial

Corifollitropin alfa's pivotal evidence comes from ENGAGE (Devroey P, Boostanfar R, Koper NP, et al., "A double-blind, non-inferiority RCT comparing corifollitropin alfa and recombinant FSH during the first seven days of ovarian stimulation using a GnRH antagonist protocol," Hum Reprod 2009;24(12):3063-3072, DOI: 10.1093/humrep/dep291), a double-blind, double-dummy, non-inferiority trial that randomized more than 1,500 women undergoing a GnRH-antagonist IVF protocol to a single 150μg dose of corifollitropin alfa or seven days of daily 200 IU recombinant FSH. Ongoing pregnancy rates were statistically similar between arms — 38.9% with corifollitropin alfa versus 38.1% with daily rFSH — meeting the trial's pre-specified non-inferiority margin, with a comparable rate of ovarian hyperstimulation syndrome (OHSS), the labeled risk shared across this site's entire fertility-stimulation cluster.

Approved across Europe and beyond, but not the US

The European Commission approved corifollitropin alfa as Elonva (Merck/Organon) on 25 January 2010 — the first sustained-activity FSH product approved anywhere — and it has since been authorized in more than 75 countries. Merck did pursue US approval too: in July 2014, the company disclosed that the FDA had issued a Complete Response Letter for its New Drug Application, declining to approve corifollitropin alfa in the US. Neither Merck nor the FDA appears to have detailed the specific deficiency behind that decision in public statements — worth knowing plainly rather than guessing at a reason, the same honest gap this site's own somatrogon page notes about a different drug's FDA rejection letter. No subsequent US resubmission or approval has followed as of this review.

Worth checking against a current source. Regulatory positions can change; if a US approval decision for corifollitropin alfa has occurred since this review, confirm it directly against the FDA's own drug database rather than assuming today's status is still current.

Current status

Elonva remains actively marketed by Merck (as MSD outside the US and Canada) across the European Union and other approved markets, and continues to be studied in newer stimulation-protocol research as of 2025-2026. It has no wellness, off-label bodybuilding or grey-market presence of any kind — a specialist-prescribed, clinic-administered fertility drug with no appeal outside that setting, the same as every other drug in this site's gonadotropin cluster.

References

  1. Devroey P, Boostanfar R, Koper NP, Mannaerts BM, Ijzerman-Boon PC, Fauser BC (ENGAGE Investigators), "A double-blind, non-inferiority RCT comparing corifollitropin alfa and recombinant FSH during the first seven days of ovarian stimulation using a GnRH antagonist protocol," Hum Reprod 2009;24(12):3063-3072, DOI: 10.1093/humrep/dep291.
  2. European Medicines Agency, Elonva (corifollitropin alfa) European Public Assessment Report (EPAR); European Commission marketing authorisation, 25 January 2010 (Merck/Organon).
  3. Merck & Co. public disclosure of an FDA Complete Response Letter for the corifollitropin alfa New Drug Application, July 2014; no subsequent FDA approval identified as of this review.