Biological
half-life measures the speed at which a
biological material is metabolized or eliminated from
an organism’s body. Half-life measures how long
exactly half of an agent takes to decay. If the biological
half-life of substance X is 2 days, after two days,
only 1/2 of the original amount will be left. After
another 2 days, only 1/2 of that half will remain, or
1/4 of the original amount, and so on until the material
has been completely eliminated. In prostate cancer treatments
using hormone therapy, LHRH agonist occupy receptors
in the brain normally occupied by normal LHRH. Because
LHRH mimics LHRH, the body begins mass producing testosterone
in a phenomenon called hormone flare that last 7 to
10 days. After the hormone flare, however, the testosterone
level will drop to castrate level because the LHRH agonist
has a longer biological half-life than LHRH. The agonist
will continually occupy these receptors until the prostate
cancer treatment is stopped.
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