Oxytocin
Oxytocin, a peptide. Posterior-pituitary nonapeptide with a disulfide bond between Cys-1 and Cys-6 forming a 6-member ring + 3-aa C-terminal tail… IV half-life 1.2 h.
Posterior-pituitary nonapeptide with a disulfide bond between Cys-1 and Cys-6 forming a 6-member ring + 3-aa C-terminal tail ending in glycine amide. Activates OXTR (Gq-coupled) in uterus (labour), breast (milk ejection), and CNS (affiliative behaviour, social cognition). Research use intranasally for trust/bonding modulation; clinical efficacy contested.
PK: Nielsen 2017 (PMID:28679021), 33 postmenopausal women, IV 10 IU, verbatim "The clearance, volume of distribution at steady state, distribution half-life, and terminal half-life were estimated to be 27 L/h, 15 L, 5.5 minutes, and 1.2 hours, respectively". The stored 0.07 h matched neither phase and appears to have been a mis-rounding of the 5.5 min DISTRIBUTION half-life; elimination is governed by the terminal 1.2 h, and the volume the same abstract states was never stored. CAVEAT: clearance rises about fourfold in late pregnancy through placental oxytocinase — 5.7 vs 1.3 L/min (PMID:2375427) — so a fixed value is wrong for any obstetric use. Infusion rate, by contrast, does not change clearance (PMID:3793853).
Pharmacokinetics
- IV — t½ 1.2 h · F 100% · Vd 15 L
Sources: PMID:28679021, PMID:2375427