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Because the growth of prostate
cancer is fueled by the male sex hormone testosterone,
doctors can use chemical castration to ablate 90 to
95 percent of the body’s supply. Chemical castration
interferes with signals in the brain that tell the testicles
to start testosterone production. The hypothalamus in
the brain first detects that levels of testosterone
are dropping and releases luteinizing hormone-releasing
hormone (LHRH)
also called gonadotropin-releasing hormone (GnRH).
LHRH or GnRH act as a messenger and fill in receptors
of the pituitary gland to report the lowering levels
of testosterone. The pituitary gland releases luteinizing
hormones (LH) that travel to the testicles.
An antagonist inhibits the action
of a cell by filling in receptors. A LHRH or GnRH antagonist
mimics the shape of normal LHRH then fills in the receptors
on the pituitary gland. Not receiving the message from
the hypothalamus, the pituitary gland does not release
LH. The testicles never produce testosterone and the
body’s levels drop.
LHRH and GnRH antagonists should
not be confused with agonists. LHRH antagonists are
generally used only for advanced prostate cancer with
bone
metastasis. Unlike the agonists, LHRH
or GnRH antagonists do not produce hormone
flare. LHRH antagonists, however, have
been known to cause severe allergic reactions with a
small number of patients. Because of this risk, LHRH
antagonists are used only for patients with advanced
prostate cancer or who refuse any other type of hormone
therapy due to preference or other side effects.
LHRH antagonist is injected through
the buttocks at a doctor’s office. The injection
will be made by either a doctor or a nurse. Two weeks
after the initial injection, the patient receives his
second injection. Two weeks after the second injection,
the patient receives his third injection. After this
first month, the patient receives the antagonist only
once a month. Patients are strongly encouraged not to
miss appointments, and to schedule those appointments
as close to exactly four weeks later as they can. After
an injection, a patient will also wait at his doctor's
office for another 30 minutes to ensure that he does
not have an allergic reaction.
LHRH antagonists are usually not
recommended for patients who have irregular heart beat,
liver problems, or osteoporosis. Patients who weigh
over 225 pounds are also not candidates for LHRH antagonists.
Patients who have one or more of these physical criteria
should speak with their doctors about whether LHRH antagonists
are right for them. LHRH antagonists could exacerbate
irregular heart beat and liver problems in addition
to risking decreasing bone density. Researchers have
found that weighing over 225 pounds could dramatically
decrease the effectiveness of the antagonists.
After the first injection, patients
should receive a blood test once every 8 weeks to ensure
that his levels of testosterone have dropped to castrate
level. Patients should also consider tests to monitor
the functioning of the liver. Patients who undergo extensive
LHRH antagonist hormone therapy run a higher risk of
developing osteoporosis.
If patients experience a changing
in the rhythm of their heartbeat or fainting, they should
contact their doctor immediately.
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