Contraception 3 Flashcards

Using the concept of first pass metabolism, explain why oral combined hormonal contraception is associated with increased risk of thromboembolic complications compared to trans-dermal and vaginal combined hormonal formulations.

1
Q

Why are oral combined hormonal contraceptives associated with increased risk of thromboembolic complications?

A
  • Blood from intestines passes through the liver first
  • Estrogen and progesterone molecules are metabolized before the blood gets to the rest of the body
  • Liver “sees” much higher drug levels than the rest of the body
  • Trans-dermal and vaginal combined hormonal formulations bypass this mechanism
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2
Q

What is the uterine first pass effect?

A
  • Vaginal administration of P and E2
  • Preferential distribution to uterus
  • Evidence
    • uterine tissue P > plasma P
    • uterine vascular P > radial artery P
    • creates secretory endometrium despite low plasma P
    • endometrial P higher after vaginal vs. IM
    • higher endometrial E2 levels after vaginal vs. oral E2
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