What is the mode of action of the injectable contraceptive method shown in the image?

NORCET 8 Prelims-2025

Pharmacology

Easy

Appeared in: NORCET 8 Prelims-2025

Explanation

The image shows Depo-Provera (medroxyprogesterone acetate), a progestin-only injectable contraceptive.
Its primary mechanism is the inhibition of ovulation, which is achieved by suppressing the release of gonadotropins (specifically the LH surge) from the pituitary gland.
A second key mechanism is the thickening of cervical mucus, which creates a barrier that prevents sperm from entering the uterus and reaching the egg.
It also causes thinning of the uterine lining (endometrium), making it unsuitable for implantation, although this is considered a secondary effect.

Option A: Progestins, the active ingredient in Depo-Provera, cause uterine smooth muscle relaxation, not contraction. This effect is beneficial in maintaining pregnancy but is not its contraceptive mechanism. Uterine contractions are stimulated by hormones like oxytocin.
Option B: While preventing fertilization and implantation is the ultimate goal of the contraceptive, this option describes the outcome, not the specific physiological mechanism of action. The question asks for the 'mode of action,' which is how the drug achieves this outcome.
Option D: Depo-Provera is a progestin-only method. The high level of progestin suppresses ovarian function, which in turn leads to significantly lower levels of endogenous estrogen, creating a hypoestrogenic state. This is the opposite of increasing estrogen levels.

Visual 1: Diagram: A flowchart illustrating the hypothalamic-pituitary-ovarian (HPO) axis, showing how exogenous progestin provides negative feedback to suppress LH and FSH, thereby inhibiting ovulation.
Visual 2: Illustration: A comparative image showing normal, thin, watery cervical mucus at mid-cycle versus the thick, scanty mucus produced under the influence of progestin, highlighting the barrier effect on sperm.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The primary mode of action for progestin-only injectable contraceptives like Depo-Provera (DMPA) as background academic context rather than a clinical decision trigger.
Patient counseling is critical when administering DMPA. Nurses must inform patients about common side effects like irregular bleeding, amenorrhea, potential weight gain, and the delayed return to fertility (up to 10-18 months) after discontinuation.
A significant concern with long-term use (greater than 2 years) is the potential for decreased bone mineral density due to suppressed estrogen levels. This is especially important for adolescents. The FDA has issued a black box warning regarding this risk.
Nurses must administer the 150 mg dose via a deep intramuscular (IM) injection in the gluteal or deltoid muscle every 3 months (12-13 weeks). It is crucial not to massage the injection site, as this can speed up absorption and reduce its duration of effectiveness.

How to Approach the Question

First, identify the drug shown in the image. The box clearly reads 'DEPO-PROVERA' and 'MEDROXYPROGESTERONE', which is a progestin-only injectable contraceptive.
Next, recall the pharmacology of progestins. Their primary contraceptive effects are related to the suppression of the hormonal cycle and changes in the reproductive tract.
Evaluate each option based on the known actions of progestin:
Does progestin increase uterine contractions? No, it relaxes the uterus.
Does it increase estrogen? No, it suppresses natural estrogen production.
Does it prevent fertilization and implantation? Yes, but how? This is the result, not the mechanism.

Concept Tested & Keywords

Concept Tested: The primary mode of action for progestin-only injectable contraceptives like Depo-Provera (DMPA).
Stem keywords: injectable contraceptive, mode of action, Depo-Provera
Lead-in keywords: What is
Clinical cues: The image shows Depo-Provera, identifying the specific drug in question as medroxyprogesterone acetate.

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