[Pharmacokinetics of 14 beta-, 15 beta-methylenestratriene STS 593 after one-time and multiple administrations to beagles].

Disposition and excretion of the estrogen derivative STS 593 [1,3-methoxy-14 beta,15 beta-methylenestra-1,3,5(10)-triene-17 beta-ol] with antifertility activity were investigated in Beagle dogs after single and repeated administration of the tritium-labelled compound. The plasma concentration vs. time courses of total radioactivity (TRA) and of the parent drug alone were estimated in conscious animals simultaneously with the urinary and fecal excretion data. From this the basic pharmacokinetic parameters were calculated and experimentally confirmed by multiple-dosing data. STS 593 differs from estradiol with respect to its higher bioavailability after oral administration; it amounts to 34-62% depending on the administration formulation. The compound is metabolized rapidly. The accumulation factor of TRA resulting from a multiple once-a-day dose regimen of STS 593 was quantified with 3.1.