Objective: The aim of this investigation is to determine whether 17alpha-hydroxyprogesterone caproate is hydrolyzed, in vitro, to 17alpha-hydroxyprogesterone and caproate.
Study design: The in vitro hydrolysis of dual radioactively labeled 17alpha-hydroxy-[3H] progesterone [14C] caproate by human plasma, hepatic and placental S9 fractions as well as recombinant esterases was investigated. The formation of [3H]-17alpha-hydroxyprogesterone and [14C]-caproate were determined with the use of high-performance liquid chromatography equipped with an online radioactivity detector. The presence and activity of carboxylesterase and butyrylcholinesterase in the human-derived preparations was confirmed by the hydrolysis of their prototypic substrates p-nitrophenyl acetate, p-nitrophenyl butyrate, and butyrylthiocholine, respectively.
Results: The aforementioned human-derived preparations hydrolyzed p-nitrophenyl acetate, p-nitrophenyl butyrate, and butyrylthiocholine. However, when 17alpha-hydroxyprogesterone caproate was incubated with the human-derived preparations under identical experimental conditions neither [3H]-17alpha-hydroxyprogesterone nor [14C]-caproate was detected.
Conclusion: 17Alpha-hydroxyprogesterone caproate is not hydrolyzed in vitro by the esterase enzymes present in human plasma, liver, preterm, or term placenta.