General classification of contraceptives
In modern pharmacology, pregnancy prevention agents are divided into several main groups. The baseline classification of hormonal contraceptives includes the following categories:
- Combined estrogen-progestogen preparations (COCs) represent the main and most extensive group on which most family planning regimens are based.
- Progestogen-only preparations—also known in medical practice as minipills.
- Emergency contraceptives—a specific group of postcoital medications used after unprotected intercourse.
Composition and safety of combined preparations
Classical combined oral contraceptives consist of two active substances. The estrogenic component is represented in the vast majority of cases by ethinylestradiol. Various synthetic progesterone analogs act as the progestogenic component.
It is important to understand the interaction between these components. The dominant contraceptive effect is always provided precisely by the progestogen component. The role of estrogens is to potentiate (significantly enhance) the inhibitory effect of progestogens on the secretion of pituitary gonadotropins.
However, the presence of estrogens requires strict safety control. Systematic estrogen intake stimulates the synthesis of procoagulants (blood clotting factors) in the liver, which directly increases the risk of thrombosis. To minimize the probability of thromboembolic complications, pharmacologists limit the dosage: in modern pills, the estrogen content usually does not exceed 35 mcg.
Depending on the variation of hormone doses during the menstrual cycle, COCs are divided into 3 types: monophasic (with a constant dose of both components), biphasic, and triphasic.
Mechanism of contraceptive action
The action of combined preparations is realized simultaneously at two levels: central and peripheral.
1. Central action (ovulation suppression) This is carried out through an effect on the pituitary gland:
- Estrogen effect: acting via a negative feedback mechanism, they suppress the production of follicle-stimulating hormone (FSH) during the proliferative phase of the cycle. As a result, the growth and maturation of follicles in the ovaries are slowed down.
- Progestogen effect: they purposefully suppress the secretion of pituitary luteinizing hormone (LH). The ultimate outcome of this combined action is the complete blockade of ovulation.
2. Peripheral action (progestogenic effects) Even if ovulation occurs, additional protection is triggered at the target organ level:
- Cervical factor: under the influence of the drugs, the cervical glands begin to produce very thick and viscous mucus. This creates a reliable mechanical barrier preventing spermatozoa from penetrating the uterine cavity.
- Tubal factor: there is a pronounced decrease in fallopian tube peristalsis. This causes impaired ovum transport—it enters the uterus prematurely or delayed, making fertilization impossible.
- Uterine factor: the drugs cause profound structural changes in the endometrium. As a result, implantation of the already fertilized egg becomes impossible. This mechanism is classified as abortifacient and is also used in medicine to terminate pregnancy.
Briefly: answers to topical questions
What specific synthetic progestogens are part of modern COCs?
Modern combined oral contraceptives contain synthetic progestogens, including:
- Norgestimate.
- Desogestrel.
- Gestodene.
- Dienogest—possesses antiandrogenic activity.
- Drospirenone—possesses antimineralocorticoid activity.
- Cyproterone—possesses antiandrogenic activity and is used, for example, as part of Diane-35.
- Levonorgestrel—a 19-nortestosterone derivative, used in COCs.
What active substances are used as emergency postcoital contraceptives?
For emergency hormonal contraception, five groups of drugs are used:
- Estrogens.
- Combined estrogen-progestogen preparations; the source indicates the composition: ethinylestradiol and levonorgestrel.
- Progestogens.
- Danazol.
- Mifepristone—a synthetic progesterone antagonist; for emergency postcoital contraception, it is used as a single dose of 600 mg within 72 hours after intercourse.
What are the absolute contraindications to prescribing COCs?
Contraindications to prescribing combined oral contraceptives include a number of pathological and physiological conditions. These include:
- Pregnancy—an absolute contraindication to hormone therapy.
- Severe liver function impairments—limit the use of steroids.
- Thrombophilias—conditions with a high risk of blood clot formation.
- Smoking—sharply increases the risk of thromboembolism when taking the medications.
Which drugs belong to the minipill group (progestogen-only contraceptives)?
Oral progestogen contraceptives (minipills) include drugs containing microdoses of synthetic progestogens. Among them are:
- Demulen—contains ethynodiol at a dose of 0.5 mg.
- Microlut—contains levonorgestrel at a dose of 0.03 mg.
- Exluton—contains lynestrenol at a dose of 0.5 mg.
- Cerazette—contains desogestrel at a dose of 0.075 mg.
What adverse effects are characteristic of the estrogenic component of COCs, aside from the risk of thrombosis?
In addition to the risk of thrombosis, the estrogenic component of combined oral contraceptives can cause a number of other side effects. These include:
- Sodium and water retention—leads to the development of edema.
- Blood pressure elevation—caused by the stimulating effect of estrogens on the renin-angiotensin-aldosterone system.
- Carbohydrate metabolism impairment—manifests as decreased glucose tolerance and elevated blood glucose levels, which can provoke latent forms of diabetes mellitus.
Remember the central mechanism of COCs through these associations: Estrogens — FSH (inhibit follicle growth), Progestins — LH (block ovulation). The peripheral action of progestins is the rule of three barriers: thick mucus (cervix), weak peristalsis (tubes), unsuitable endometrium (uterus).
Class and exam questions
Which COC component is responsible for the primary contraceptive effect?
The dominant contraceptive effect is provided by the progestogen component. Estrogens act as synergists, potentiating the inhibitory effect of progestogens on pituitary gonadotropin secretion.
Why is the estrogen dose strictly limited in modern COCs?
Systematic estrogen intake stimulates the synthesis of procoagulants in the liver. Dose limitation to 35 mcg is necessary to reduce the risk of thrombosis and thromboembolic complications.
How do progestogens prevent sperm penetration?
They act on the cervical glands, causing them to produce very thick and viscous mucus. This creates a reliable mechanical barrier in the path of spermatozoa.
What is the uterine factor in contraceptive action?
Under the influence of the drugs, structural changes occur in the endometrium, making the implantation of a fertilized egg impossible. This same abortifacient mechanism is used to terminate pregnancy.
What else to study on this topic
- Features and administration of progestogen-only pills (mini-pills).
- Mechanism of action of emergency (postcoital) contraceptives.
- Differences in dosing schedules for monophasic, biphasic, and triphasic COCs.
- Synthetic progestogens: types and pharmacological profiles.
- Abortifacient mechanism of action of contraceptives at the endometrial level.
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