- Objective: To compare the pharmacokinetics of a long-acting FSH analog containing the hCG-β carboxyterminal peptide (recombinant hFSH–CTP) with native recombinant hFSH and describe the pharmacodynamics of recombinant hFSH–CTP after SC injection in female rhesus monkeys. Design: Rhesus monkey study. Setting: Academic research environment. Animal(s): Ten female rhesus monkeys. Intervention(s): Recombinant hFSH and recombinant hFSH–CTP were administered via a single SC or IV dose to rhesus monkeys, and serial phlebotomy was performed (n = 2 and n = 4 for SC recombinant hFSH and recombinant hFSH–CTP, respectively; for IV dosing, n = 1 in each group). An additional two monkeys were pretreated with SC ganirelix and received SC recombinant hFSH–CTP after confirmation of pituitary suppression. Main Outcome Measure(s): Plasma disappearance rate of recombinant hFSH and recombinant hFSH–CTP and serum estradiol levels. Result(s): The elimination half-life of recombinant hFSH–CTP was twofold and fourfold longer than that for recombinant hFSH after SC and IV dosing, respectively. The absorption half-life was approximately threefold longer for recombinant hFSH–CTP than for recombinant hFSH after SC administration. Recombinant hFSH–CTP stimulates estradiol secretion for 5–7 days after an isolated SC dose. Conclusion(s): Addition of the hCG-β carboxyterminal peptide to hFSH-β results in an FSH analog with longer absorption and elimination half-lives compared with native hormone. This analog is capable of prolonged ovarian stimulation in rhesus monkeys after an isolated SC injection.