Mode of Action:
Primary Mechanism of Action
– is anovulation (no release of eggs).
Inhibition of ovulation: The active ingredients in injectable
contraceptives affect the hypothalamus and pituitary glands. The result is a
reduction in Follicle Stimulation hormone (FSH) and Luteinizing Hormone (LH),
both of which are necessary for ovulation (monthly release of eggs).
Secondary Mechanisms of
Action (Less effective)
Thickens the cervical
mucus: The thicker mucus renders sperm
penetration difficult.
Thins the endometrial
lining: As a result of the high
progestin and low estrogen levels, the endometrium becomes thin and atrophic,
thus affecting implantation. This is not a functional mechanism of action
because ovulation rarely occurs and sperms are inhibited from ascending above
the cervix.
Availability
and Brand Names:
Norethisterone enanthate, available as a thick oily fluid,
is given in a dose of 200mg (in ml) every eight weeks. The viscosity of the
liquid at low temperatures is high and it is recommended that the ampoule be
immersed in warm water just before administration. DMPA, the most widely used
progestin-only injectable, is also known as “the shot”, “the jab”, the
injection, Depo, Depo-Provera, Megestrol, and Petogen.
New
formation:
A formulation of DMPA has been developed specifically for
injection into the tissue just under the skin (subcutaneously).DMPA-SC is available in prefilled syringes,
including the single-use Uniject system. These prefilled syringes will have
special short needles meant for subcutaneous injection. With these syringes,
women could inject DMPA themselves. DMPA-SC was
approved by the United states Food and Drug Administration in December 2004.
Depo-Provera
¨Advantages as Contraceptives:
Although hormonal methods
are not the first choice for breast-feeding women, in most studies DMPA has had
no effect on breast-milk production or has increased the volume of breast milk.
No oestrogen related side
effects
No daily commitment (like
pill or barrier methods)
Very effective
Private
Many non-contraceptives
health benefits (myoma dysmenorrhoea, endometriosis).
Negative sides (Minuses )
of Depo-Provera (Limitations of
Depo-Provera as a contraceptive):
1) Menstrual
Cycle disturbances: This may result spotting, breakthrough bleeding and
short-lasting amenorrhea are the only relatively frequent side effects.
Amenorrhoea can be an advantage if women are fully informed that this is
natural and will not cause any harm to them.
2 ) Delay in return of
fertility: Since they are long acting they cannot be easily discontinued or
removed from the body if a complication occurs or if pregnancy is desired.
Though there is some delay Injectables are completely reversible and do not
cause infertility.
2) Injectable contraception does not provide any
protection against STIs/HIV:
3) Weight gain is rare
about 2.4kg on an average, in the first year. Weight gain can be
advantage for many women.
Injectable were initially.
Benefits
of Depo Provera as a Contraceptive
1) Does not affect breast-feeding.2) Highly effective (0.3-1
pregnancies per 100 women during the first year of use).3) Rapidly effective (within 24 hours)
following administration Intermediate-term method (2-3 months of protection per
injection).4) Does not affect breast feeding.
How
effective as contraceptive?? Reliability-as contraceptive (contraceptive
efficacy) –
When administered during the first five days
of the menstrual cycle, Depo-Provera provides contraceptive efficacy from
the very first cycle and no additional barrier method need be employed in the
first month. Therefore Depo provera is one of the most effective family planning methods: less than 1 pregnancy per
100 users per year. Effectiveness depends on
getting injections regularly: Risk of pregnancy is greatest when a woman misses
an injection. As commonly used, about 3 pregnancies per 100 women using
progestin-only injectables over the first year. This means that 97 of every 100
women using injectables will not become pregnant.
Who are
ideal Candidate: for Depo provera?
The daily does received by
the child during the sue of progestin-only methods can be estimated from the
concentration of steroids in milk, assuming that a 3 month old, fully nursed
infant has a total milk intake of 600-800 ml/24 h r The estimated daily dose received by a child
fully nursed by a mother using implants ins in the same range estimated for
progestin-only pills (on order of the nanogram) and is much smaller than that
received by infants breastfeed by mothers using progestin-only injectables (on
order of the microgram). The main advantage of DMPA is that it has almost
only progestational activity (DMPA), whereas others have some estrogenic (NET) or androgenic
(levonorgestrel) activity, and their impact on the infant many differ.
It can be used in location period.
The concerns related to the transfer of steroids to the infant have prompted
the recommendation to delay its use beyond 6 to 8 weeks postpartum. This
interval is a critical period in human development because the central nervous
system has its highest extra-uterine growth rate at this time and may be more
susceptible to deleterious stimuli. Moreover, the first postpartum weeks are
also the period in which there liver and other systems are less mature, and
there is no information on how the child handles exogenous steroids, even If
administered in the minimal amounts found in maternal milk. In this period, the
maternal endogenous production of ovarian steroids is reduced to a minimum
amount, suggesting that nature has taken care of steroid-free milk in the first
weeks postpartum. Delaying initiation of a contraceptive method from
immediately after birth to 6 weeks postpartum does not expose a fully nursing
amenorrhoeic woman to the risk of pregnancy. Better alternatives for women who
want a contraceptive method in this early postpartum period are non-hormonal
methods or hormonal methods based on orally inactive steroids such as Nestorone
and progesterone.
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