Levonorgestrel, Pharmacokinetics, Efficacy and Safety 41do not constantly inhibit ovulation. LNG in such low doses can still remain
effective as a contraceptive by acting at the level of the cervical mucus, by
significantly decreasing the amount, ferning and spinnbarkeit of cervical
mucus, while at the same time increasing the viscosity. Under the effect of
progestins, cervical mucus scores do not exhibit the normal mid-cycle peak,
cervical mucus receptivity to sperm is lowered, sperm penetration in cervical
secretion is inhibited and the ovulatory peak of the karyopyknotic index of
vaginal cytology is suppressed. After insertion of subcutaneous LNG-
delivering implants (Norplant), cervical mucus scores decrease within one
week, indicating the profound effect of LNG on the cervical mucus, even in
the event of possible ovulation [23].
Levonorgestrel Combined Oral Contraceptive
LNG efficacy has been determined in various formulations in the form of
OCP, patches, implant, and IUD. In OCP the efficacy is determined along with
estrogen. The combined oral contraceptive pill is an effective contraceptive
method which can also offer other benefits. Pills containing LNG or
norethisterone in combination with 35 mg or less ethinyloestradiol are
considered first-line. They are effective if taken correctly and have a relatively
low risk of venous thromboembolism [24].
LNG containing OCP are being used in different formulations. Newer
extended regimens of LNG containing OCP have been highly effective at
decreasing the frequency of menstrual bleeding. Many women would prefer to
eliminate or reduce the frequency of scheduled bleeding if given the choice
[25, 26]. Loudon et al. were the first to show that reducing withdrawal
bleeding to four times a year (using an oral contraceptive containing EE 50 μg
plus lynestrenol 2.5 mg) was both acceptable and effective: 82% of the 196
women experienced fewer menses and a reduction in menstrual and
premenstrual symptoms [27]. This regimen was not introduced into clinical
practice until the development of combined OCP with minimum feasible
estrogen daily dose and the introduction of a series of new progestins.
In last several years new options have been considered to decrease the
frequency of free intervals or to eliminate them altogether [28]. In addition,
extended pill use (with or without interruption) has also been advocated as a
maintenance treatment for endometriosis-associated pelvic pain in women not
wishing to become pregnant [29, 30] and to avoid menstruation-associated
symptoms such as migraine headaches[31] and premenstrual syndrome[32].