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Pharmacokinetics of Nandrolone Decanoate


Nandrolone decanoate

Upon intramuscular injection in oil, which results in the formation of a long-lasting depot in the muscle, nandrolone decanoate is stored unchanged and is slowly absorbed into the body. Once in the circulation, it is converted into nandrolone, which is the active form of the drug. There is a sharp spike in nandrolone levels 24 to 48 hours after an intramuscular injection of nandrolone decanoate, followed by a steady decline to baseline levels within approximately two or three weeks. The bioavailability of nandrolone decanoate is 53 to 73% with intramuscular injection and varies with the site of injection, with the highest bioavailability seen when injected into the gluteal muscle. Like testosterone, nandrolone is highly protein-bound and is present in the blood in both bound and free fractions. It has very low affinity for sex hormone-binding globulin (SHBG), about 5% of that of testosterone and 1% of that of DHT.

Nandrolone decanoate is rapidly hydrolyzed in the blood by esterases into nandrolone, with a terminal half-life of one hour or less. It does not appear to be hydrolyzed in muscle or fat. The metabolism of nandrolone occurs in the liver and is very similar to that of testosterone, including reduction by 5α-reductase and 5β-reductase, dehydrogenation by 3α-hydroxysteroid dehydrogenase, 3β-hydroxysteroid dehydrogenase, and 17β-hydroxysteroid dehydrogenase, and conjugation. The metabolites of nandrolone include 5α-dihydronandrolone, 19-norandrosterone, and 19-noretiocholanolone, with 19-norandrosterone being the major metabolite. Other metabolites include 19-norandrostenedione, 19-norandrostanediols, 19-norepiandrosterone, and conjugates. Nandrolone also undergoes aromatization into estradiol similarly to testosterone, though at a rate of only about 20% of that of testosterone or possibly even less; one study found virtually no aromatization of nandrolone in men.

The elimination half-life of nandrolone decanoate administered by intramuscular injection is approximately 6 to 12 days. Studies that have assessed the duration of nandrolone decanoate via its anabolic effects, for instance on nitrogen balance, have found that a single 50 to 100 mg intramuscular injection had a duration of about 18 to 25 days. The blood half-life for the combined process of hydrolysis into nandrolone and elimination of nandrolone is 4.3 hours. Nandrolone and its metabolites are excreted in the urine, mainly in the form of conjugates.

Although nandrolone decanoate is usually administered by intramuscular injection, it has been found to be similarly effective when administered by subcutaneous injection. The pharmacokinetics of nandrolone decanoate via subcutaneous injection closely resemble those of intramuscular injection. However, subcutaneous injection is considered to be easier, more convenient, and less painful compared to intramuscular injection. In addition, research suggests that most intramuscular injections in practice are in fact subcutaneous injections.


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