Drugs used as contraceptives Flashcards
What effects does progesterone have on the body that make it an effective contraceptive?
alters viscosity and pH of cervical mucus to make inhospitable to sperm
chronic use of progesterones inhibit egg implantation in the endometrium
What type of oestrogen is most commonly used in the combined oral contraceptive pill?
ethinylestradiol
What type of progesterone is used in the combined pill?
levenorgestrel
could be norethisterone or ethynodiol
What is the mode of action of the combined pill?
Oestrogen inhibits secretion of FSH via negative feedback on the anterior pituitary, and thus suppresses development of the ovarian follicle
Progestogen inhibits secretion of LH and thus prevents ovulation; it also makes the cervical mucus less suitable for the passage of sperm.
Oestrogen and progestogen act in concert to alter the endometrium in such a way as to discourage implantation.
How should the combined contraceptive pill be taken?
taken for 21 consecutive days followed by 7 pill free days which causes a withdrawal bleed
continue taking the pill everyday as normal after then
POP is taken continuously
What is in the morning after pill?
a large dose of progesterone
levornogesterol or ulipristal acetate
What are the contra-indications for the pill?
pre-existing cardiovascular disease
obese
smoker over 40
hypercholesterolaemic
liver cirrhosis
‘oestrogen-sensitive’ breast/bowel cancer
What prostaglandin may be used to induce co-ordinated muscle contractions?
PGE-analogues
dinoprost and misoprostol
mag be given as gels intravaginally
How is oxytocin release stimulated?
in response to cervical dilation and by suckling
How can oxytocin induce labour?
causes regular co-ordinated contractions that travel from the fundus of the uterus to the cervix
Why is the uterus highly sensitive to oxytocin at full term?
oestrogen induces oxytocin receptor synthesis
at full term there are high levels of circulating oestrogen
Why are too high doses of oxytocin fatal to the foetus when given in labour?
too higher doses can cause sustained contractions that interfere with blood flow through the placenta and cause foetal distress or death
How many days into gestation are medical terminations legal in the UK?
63
How does mifepristone work?
progesterone receptor antagonist that causes endometrial degeneration and sensitises uterine contractions to prostaglandins
What kind of drugs are oestrogen and progesterone?
(what do they target?)
steroid receptor agonists
Why is there a small increased risk of thrombo-embolic events if using contraceptives containing oestrogens?
oestrogens increase levels of some circulating blood clotting factors and increase the aggregatory potential of platelets
What are hormone responsive elements (HREs)?
short sequence of DNA within the promotor of a gene that is able to bind a specific hormone receptor (oestrogen/progesterone and receptor complex) and therefore regulate gene transcription
Why might you offer someone the POP rather than combined pill?
oestrogen may be contra-indicated
What are the effects of oestrogen steroid receptor complexes binding to HREs?
increased clotting factors and platelet adhesivity (increased risk of thrombo-embolism)
reduces bone loss, increases bone density
up-regulation of progesterone receptors
What is gemeprost?
a methyl ester analogue of PGE1 that is used with mifepristone
helps reduce obstretic bleeding by causing vasoconstriction
What are the effects of progesterone on uterine contractility?
decreases it and inhibits lactation
What is the effect of oestrogen on gonadotroph cell secretions in the pituitary?
suppresses them
