Disappearance of prostaglandins F2alpha and 15-methyl F2alpha from amniotic fluid as measured by radiommunoassay.

A sensitive and relatively specific radioimmunoassay for 15 (S) 15 methyl prostaglandin F2alpha was used to determine the levels of the drug in amniotic fluid after it had been injected intra-amniotically for termination of second trimester pregnancy. The disappearance of the free acid (tham salt) and methyl ester of the prostaglandin analogue were similar. The results of this preliminary study suggest that the drug rapidly equilibrates in the fluid and this followed by a slow removal from the amniotic sac. A comparison with a similar study with PGF2Alpha revealed that the analogue had a longer half-life in the amniotic fluid.