The pharmacokinetics of steroïds used in estroprogestative
contraception.
Christian Jamin
Service Gynécologie Obstétrique, CHU Bichat, Paris, France
Since the day contraceptives were marketed, the tendency has
been to lower steroids doses which, one hoped, would lower secondary effects and
improve tolerance.
At first improvements were spectacular but then, due to the
rarity of secondary effects, results became difficult to measure. The
contraceptive effect of low dose products depends mainly on progestins, which
dose reaches a bottom level due to its blocking power. The progestin dose
determines the oestrogen dose and the adequacy of their proportions as well as
the quality of cycle control. With the progestins available today, the minimum
estrogen dose is 20 micrograms per day for a 21 days cycle.
It has been possible to further diminish the dose of progestins,
and consequently of estrogens, by increasing the duration of treatment to 24
days per cycle, with a slight deterioration of cycle control. The cutaneous way
of administration by patch did not change this last point. However the vaginal
way with a ring has given circulating levels and areas under the steroids curve
equivalent to those of a 15 micrograms pill, but this time with an improvement
of cycle control. Besides, circulating levels are remarkably stable with this
ring.
Although studies are rarely comparative, general tolerance also
seems to have been improved.