Progestin-Only Contraceptives

Mechanism

Mechanism of Action

Progestin-only contraceptives exert their effect selectively peripherally and centrally without requiring the co-administration of estrogens.

The Progestin-Only Pill (Desogestrel)

It is a low-dose continuous daily oral contraceptive:

• Inhibits ovulation in 97-99% of cycles through moderate pulsatile suppression of LH.
• Induces dense thickening of cervical mucus to block sperm passage.
• Causes unstable progressive endometrial atrophy.

Long-Term Devices (LNG-IUD / Implant)

Highly effective prolonged release systems (LARC):

• IUD with Levonorgestrel: Releases micrograms of LNG daily locally into the endometrial cavity, inducing a potent decidual foreign body reaction, glandular atrophy marking thick mucus, and inhibition of spermatic capacitation.
• Subcutaneous implant (Etonogestrel): Releases continuous systemic etonogestrel, achieving total ovulatory suppression by hypothalamic-pituitary blockade over a period of 3 years.

Pharmacokinetics

Pharmacokinetics

• Desogestrel (Oral): It is a prodrug that is rapidly absorbed and metabolized in the intestinal wall and liver to its active form: etonogestrel. Its bioavailability is 70%. It binds to albumin and sex hormone binding globulin (SHBG). Elimination half-life of about 30 hours.
• IUD-Levonorgestrel (Local): Initially releases 20 µg of LNG daily directly into the endometrial endometrium, gradually decreasing to about 10 µg after 5 years. Plasma concentrations of LNG are minimal and stable, limiting systemic metabolic adverse effects.
• Etonogestrel Implant (Systemic): Initially releases 60 to 70 µg of etonogestrel per day, progressively decreasing to about 25-30 µg at the end of its third year of useful life.

Indicators and dose

Indications

• Contraception of choice in women with an absolute contraindication to the use of estrogens (e.g., history of VTE, hypertension, migraine with aura, or smoking over 35 years of age).
• Contraception of choice during exclusive breastfeeding.
• Treatment of severe idiopathic menorrhagia or secondary to uterine myomatosis (especially the LNG IUD).
• Adjuvant treatment of simple endometrial hyperplasia without atypia.

Dosage and Schemes

• Desogestrel (Pill): 75 µg orally once a day uninterruptedly and at the exact same time (a delay of more than 12 hours in taking requires the use of a rescue barrier method).
• IUD with LNG (Mirena): Inserted by qualified gynecological personnel into the uterine cavity within the first 7 days of the cycle; Approved duration of up to 5 to 8 years according to medical indication.
• Subcutaneous implant (Implanon): Inserted subdermally on the inner surface of the non-dominant arm; Maximum recommended duration of 3 years of effectiveness.

Pregnancy and Breastfeeding

Contraindicated in pregnancy. In breastfeeding, they are the contraceptives of choice recommended by all clinical guidelines from the sixth week postpartum (and even earlier according to WHO guidelines); They do not alter the quality or quantity of breast milk produced and do not negatively affect the normal development of the infant.

Security

Contraindications

• Severe active liver disease (decompensated cirrhosis or liver tumors).
• Active hormone-sensitive breast cancer or within the last 5 years.
• Uterine bleeding of unknown origin (until endometrial malignancy is ruled out).
• Active acute venous thromboembolism (e.g., active non-anticoagulated DVT).

Adverse Effects (ADR)

• Bleeding pattern alterations: The most common adverse effect and frequent cause of treatment abandonment. It causes unpredictable irregular bleeding, prolonged intermenstrual dripping (spotting) or secondary amenorrhea (clinically desired in many patients after several months of use).
• Minor androgenic effects: Mild acne, transient mastalgia, minor fluid retention, headache and emotional fluctuations.
• Functional ovarian cysts: Development of persistent follicles that do not complete ovulation; usually asymptomatic and self-limited.