Pharmacodynamics<unk>  is a potent agonist of the AR. It has an affinity (Kd) of 0.25 to 0.5 nM for the human AR, which is about 2- to 3-fold higher than that of testosterone (Kd = 0.4 to 1.0 nM) and the dissociation rate of<unk>  from the AR is also about 5-fold slower than that of testosterone. The EC50 of<unk>  for activation of the AR is 0.13 nM, which is about 5-fold stronger than that of testosterone (EC50 = 0.66 nM). In bioassays,<unk>  has been found to be 2.5- to 10-fold more potent than testosterone. Upon intramuscular injection in rats,<unk>  is about 1.5- to 2.5-fold the potency of testosterone. Unlike testosterone and various other AAS,<unk>  cannot be aromatized, and for this reason, poses no risk of estrogenic side effects like gynecomastia at any dosage. In addition,<unk>  cannot be metabolized by 5α-reductase (as it is already 5α-reduced), and for this reason, is not potentiated in so-called "androgenic" tissues like the skin, hair follicles, and prostate gland, thereby improving its ratio of anabolic to androgenic effects. However,<unk>  is nonetheless described as a very poor anabolic agent. This is attributed to its high affinity as a substrate for 3α-hydroxysteroid dehydrogenase (3α-HSD), which is highly expressed in skeletal muscle and inactivates<unk>  into 3α-androstanediol, a metabolite with very weak AR activity. Unlike<unk> , testosterone is very resistant to metabolism by 3α-HSD, and so is not similarly inactivated in skeletal muscle. For the preceding reasons,<unk>  has been described as a "partial androgen". Pharmacokinetics Absorption The bioavailability of<unk>  differs considerably depending on its route of administration. Its oral bioavailability is very low, and<unk>  has been considered to be ineffective by the oral route. However, it has been used orally, and is described as a weak AAS by this route. The transdermal bioavailability of<unk>  is approximately 10%. Its bioavailability with intramuscular injection, on the other hand, is complete (100%). Doses of topical<unk>  gel of 16, 32, and 64 mg have been found to produce total testosterone and DHT levels in the low, mid, and high normal adult male range, respectively. Distribution The plasma protein binding of<unk>  is about 98.5 to 99.0%. It is bound 50 to 80% to sex hormone-binding globulin, 20 to 40% to albumin, and less than 0.5% to corticosteroid-binding globulin, with about 1.0 to 1.5% circulating freely or unbound. Metabolism The terminal half-life of<unk>  in the circulation (53 minutes) is longer than that of testosterone (34 minutes), and this may account for some of the difference in their potency. A study of transdermal<unk>  and testosterone therapy reported terminal half-lives of 2.83 hours and 1.29 hours, respectively.
Androstanolone
Cloxotestosterone acetate
Norethandrolone
Drostanolone propionate
Oxandrolone
Testosterone undecylenate
Testosterone cypionate
Nandrolone propionate