Abstract Study question Are serum FSH levels after single subcutaneous dosing of HP-hMG in a liquid formulation and a powder formulation bioequivalent? Summary answer The 90% CIs for the geometric mean ratios of serum FSH AUCt and Cmax were both within 0.8000–1.2500, thus the two formulations are bioequivalent. What is known already For several decades, HP-hMG (Menopur) has been used for the treatment of infertility; its efficacy and safety compared to other gonadotropins have been consistently demonstrated in several prospective, randomised controlled trials and meta-analyses (Deeks et al 2018; Bordewijk et al 2019). Menopur powder for reconstitution is available in multidose and single dose formulations. Up to 3 single dose vials (each containing 75 IU) may be dissolved into 1 mL solvent for administration. Recently, and for the first time, Menopur has been successfully formulated in a stable, ready-to-use solution for injection, which may be administered by a pre-filled pen. Study design, size, duration This was a randomised, two-way crossover, single dose, bioequivalence trial comparing Menopur liquid injected by pre-filled pen, with Menopur powder injected by conventional syringe and needle. The primary endpoints were AUCt and Cmax of baseline-adjusted FSH. Pituitary-suppressed, healthy women were randomised to receive one treatment sequence including a single subcutaneous injection of 450 IU Menopur liquid (600 IU/0.96 mL) and of 450 IU Menopur powder by two subcutaneous injections of 225 IU in 1 mL. Participants/materials, setting, methods Blood samples were collected pre- and post-dose, until 9 days after each injection. The PK parameters of FSH and hCG were assessed by noncompartmental methods with adjustment for endogenous pre-dose levels. Highly sensitive and specific electrochemiluminescence immunoassays were used for quantification and the LLOQ of the FSH and hCG assays were 1.47 mIU/mL and 0.5 mIU/mL, respectively, and the total validated CV was within 5% for both assays. Main results and the role of chance In total, 76 women were randomised and 56 completed the trial. The main reason for discontinuation was insufficient pituitary suppression prior to the second administration of HP-hMG. The mean FSH and hCG serum concentration-time profiles were comparable between the two HP-hMG formulations. The geometric mean ratios and 90% confidence intervals of FSH for HP-hMG liquid versus HP-hMG powder were 1.12 [1.0562; 1.1889] for AUCt and 1.17 [1.0946; 1.2490] for Cmax, showing that the two formulations were bioequivalent. Maximal serum FSH concentrations were reached at 18.19 h for HP-HMG liquid and 15.55 h for HP-hMG powder. In addition to FSH, the PK parameters for hCG were compared between the two HP-hMG formulations. The geometric mean ratios and 90% confidence intervals for HP-hMG liquid versus HP-hMG powder were 0.93 [0.86; 1.01] for AUCt and 0.94 [0.86; 1.02] for Cmax. There was no difference between the two groups in the incidence or severity of adverse events, and both preparations were well tolerated. Mild injection site reactions were less common after administration of HP-hMG liquid by a single injection compared to HP-hMG powder by two injections and were mostly related to pain and erythema after drug administration. Limitations, reasons for caution This bioequivalence study is based on the comparison of single dose administrations in healthy female volunteers of reproductive age. Wider implications of the findings: The new HP-hMG solution for injection in a pre-filled pen will deliver the efficacy and safety of Menopur in a convenient delivery device. Trial registration number NA