An individual with a high BMI may exhibit a different elimination half-life of testosterone esters compared to a low BMI user. Two individuals could simultaneously administer an intramuscular injection of testosterone cypionate, yet one individual will likely eliminate it sooner from his system than the other. While testosterone enanthate stays in a person’s system for longer than propionate esters, it is eliminated nearly 2-fold quicker than cypionate formats.
Two of the immediate metabolites of testosterone, 5α-DHT and estradiol, are biologically important and can be formed both in the liver and in extrahepatic tissues. Certain cytochrome P450 enzymes such as CYP2C9 and CYP2C19 can also oxidize testosterone at the C17 position to form androstenedione. In addition to 6β- and 16β-hydroxytestosterone, 1β-, 2α/β-, 11β-, and 15β-hydroxytestosterone are also formed as minor metabolites. The 6β-hydroxylation of testosterone is catalyzed mainly by CYP3A4 and to a lesser extent CYP3A5 and is responsible for 75 to 80% of cytochrome P450-mediated testosterone metabolism. A small portion of approximately 3% of testosterone is reversibly converted in the liver into androstenedione by 17β-HSD. The conjugates of testosterone and its hepatic metabolites are released from the liver into circulation and excreted in the urine and bile. Androsterone and etiocholanolone are then glucuronidated and to a lesser extent sulfated similarly to testosterone.
The elimination half-life of testosterone varies depending on the route of administration and formulation and on whether or not it is esterified. A single 50 mg testosterone pellet implanted every 4 to 6 months has been found to result in testosterone levels of 70 to 90 ng/dL in women. Levels of testosterone with intramuscular injections of testosterone cypionate were about 700 ng/dL for 100 mg/week, 1100 ng/dL for 250 mg/week, and 2000 ng/dL for 500 mg/week. Due to their varying and different elimination half-lives, the different intramuscular testosterone esters are administered with differing frequencies. These preparations are prodrugs of progesterone that have a long-lasting depot effect when injected into muscle or fat, ranging from days to months in duration. Subsequently, testosterone levels steadily decline, reaching levels of about 700 ng/dL after 4 hours and levels of about 400 ng/dL after 8 hours. Subsequently, however, non-scrotal testosterone patches with special permeation enhancers that could successfully increase testosterone levels were developed and marketed.
Though saliva tests have advantages of low cost and minimal invasiveness, they are not yet accurate enough to serve as a viable modality of testosterone testing. As of 2005, the World Anti-Doping Agency (WADA) had T/E ratios set at "4."  Should an individual’s urine contain an abnormal ratio of T/E, he/she may be considered to have used exogenous testosterone. Urine is typically assessed for testosterone/epitestosterone (T/E) glucuronide ratio with various thresholds or "cutoff" values. Therefore you’re more likely to test positive for elevated testosterone if you had utilized it intramuscularly than orally or transdermally. However, if the testosterone was administered orally, detection within urine may be minimized to just a few hours. A urinalysis will accurately determine whether testosterone was administered intramuscularly for a relatively long duration.
Meanwhile, long-acting injectables, specifically testosterone undecanoate, require decreased frequency of administration, with some manufacturers recommending dosing only at weeks 0 and 4 and then every 10 weeks thereafter16. Available in multiple delivery methods, several different types of T therapies exist including intranasal gels, oral pills, intramuscular (IM) injections, transdermal gels and patches, and subcutaneous (SQ) pellets7,15. However, coinciding with an FDA communication about potential cardiovascular events following testosterone therapy, there was a decrease of 3.2% use of testosterone in men in 2013 to 1.67% in 2016, with new users decreasing from 1.26% to 0.48%5. For instance, Canada had a four-fold increase in per capita testosterone prescribing due to internet pharmacies physically based in the country which are not subjected to national prohibitions of import/export controls of androgens4. In the former case, testosterone (T) replacement is prescribed for pathologic androgen deficiency, including disorders affecting the hypothalamic-pituitary-testicular (HPT) axis where luteinizing hormone or testosterone secretion is reduced.

Gender: Female

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