Absorption by route of exposure The absorption after oral dosing
is rapid for testosterone and probably for other anabolic
steroids, but there is extensive first-pass hepatic metabolism
for all anabolic steroids except those that are substituted at
the 17-alpha position.
The rate of absorption from subcutaneous or intramuscular depots
depends on the product and its formulation. Absorption is slow
for the lipid-soluble esters such as the cypionate or enanthate,
and for oily suspensions.
Distribution by route of exposure The anabolic steroids are
highly protein bound, and is carried in plasma by a specific
protein called sex-hormone binding globulin.
Biological half-life by route of exposure The metabolism of
absorbed drug is rapid, and the elimination half-life from
plasma is very short. The duration of the biological effects is
therefore determined almost entirely by the rate of absorption
from subcutaneous or intramuscular depots, and on the de-esterification
which precedes it (Wilson, 1992).
Metabolism Free (de-esterified) anabolic androgens are
metabolized by hepatic mixed function oxidases (Wilson, 1992).
Elimination by route of exposure After administration of
radiolabelled testosterone, about 90% of the radioactivity
appears in the urine, and 6% in the faeces; there is some
enterohepatic recirculation (Wilson, 1992).