Cetrorelix
Cetrorelix, a peptide. Decapeptide GnRH antagonist (D-Nal⁶ substitution and acetylated N-terminus) developed from ovine GnRH-antagonist… Subcutaneous half-life 2.4 d.
Decapeptide GnRH antagonist (D-Nal⁶ substitution and acetylated N-terminus) developed from ovine GnRH-antagonist templates. In controlled ovarian stimulation, direct GnRH-R blockade prevents the premature LH surge without the 2-week agonist down-regulation protocol — enabling shorter IVF cycles. Single 3 mg dose covers ~4 days; multiple 0.25 mg daily doses dial the antagonism more precisely.
PK: bioavailability re-cited and half-life re-sourced 2026-09-06. F 0.85 is correct but belonged to Pechstein 2000 (PMID:10709155), IV n=5 and SC n=6, verbatim "Average absolute bioavailability after SC administration was 85%" — a true absolute value against an IV arm. The half-life 56.9 h comes from Nagaraja 2000 (PMID:11180022), 36 healthy premenopausal women, verbatim "a terminal half-life of 56.9 +/- 27.1 hours"; the stored 63 h appears in no paper, and the previous citation (PMID:9806255) reports only ranges, 5-10 h single-dose and 20-80 h multiple-dose. V 70 L and ka 0.7 /h dropped: no abstract states either, and the 63 h / 70 L pair looks label-derived. PK: ABSORPTION RATE AUTHORED FROM THE CETROTIDE LABEL. This row carried no ka, so the solver substituted 1.0/h and put the peak at 4.5 h. Source, verbatim from the current FDA label (DailyMed setid aca7768e-28a7-4027-b1d8-e66247665f79): From the label pharmacokinetic table, "t max median (min-max) [h] 1.5 (0.5-2)" for the 3 mg single dose — the column whose half-life, 62.8 h, is the one this record stores. PUBMED HAS THIS NOWHERE — 27 targeted searches across two passes returned four usable peak times for this whole class, because Tmax is a label figure that rarely reaches an abstract. A regulatory label is already a first-class source in this schema. With the stored half-life fixing ke, Tmax solves uniquely for ka by inverting the model own definition, ln(ka/ke)/(ka-ke) = Tmax — ARITHMETIC, NOT AN ESTIMATE — giving 3.849/h, which reproduces 1.5 h on substitution. EXPOSURE IS UNCHANGED: the absorption rate cancels out of AUC, so only the shape moves.
Pharmacokinetics
- Subcutaneous — t½ 2.4 d · F 85% · ka 3.849 h⁻¹
Sources: PMID:9806255, PMID:11180022, PMID:10709155