Metabolism of a new synthetic progestagen, Org 2969, in female volunteers. The distribution and excretion of radioactivity after an oral dose of the labelled drug

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Abstract
: The metabolism of a new synthetic progestagen, Org 2969 was studied in 4 healthy female volunteers. During the first part of the study (Phase I), the volunteers ingested 50 μg (about 0.1 mCi) of [16-3H]Org 2969 together with 50 μg of ethinyloestradiol as a single dose. During the second part of the study (Phase II), a 10-day pre-treatment with the same dosage of nonradioactive compound preceded the administration of the radioactive steroid. A peak level of total radioactivity, representing 3.16–5.02% of the dose given/l of serum, was achieved within 2–3 h in Phase I. During Phase II, the corresponding figures were 4.54–5.13% after 1.5–3 h. The difference was mainly due to an increase of freely-extractable steroids during Phase II. The difference can at least partly be explained by assuming a change in the kinetics of the metabolism of Org 2969 by pre-treatment with Org 2969 and ethinyloestradiol. The mean recovery of radioactivity in urine and faeces was 83.0%/48.1%/34.9% (total/urine/faeces) of the total dose in Phase I and 76.1%/45.2%/30.9% during Phase II. The differences in the total excretion and in the radioactivity excreted in the faeces were significant.

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