Almost a decade later, a study comparing the pharmacokinetics of testosterone esters administered via IM or SC route to hypogonadal men was performed (25). As discussed, SC administration of testosterone esters should result in a more stable absorption and release of testosterone into the circulation due to less fluctuation of lymphatic flow in the hypodermis with physical activity. Since the blood flow at the site of drug administration influences the pharmacokinetics of the administered drug, SC injections display more stable vascular absorption patterns compared to IM injection. As the lymphatic drainage from SC tissue is largely dependent on intrinsic pumping, while IM lymphatic flow is also substantially influenced by extrinsic pumping during physical activity (43), these drainage patterns suggest that testosterone esters administered SC likely have more stable absorption kinetics compared to IM administration. Therefore, the pharmacokinetics of testosterone esters administered via IM vs SC route will vary according to the lymphatic circulation of the tissue. Injectable forms of testosterone can cause a lung problem called pulmonary oil microembolism (POME). The FDA has required that testosterone pharmaceutical labels include warning information about the possibility of an increased risk of heart attacks and stroke. Other side effects include increased hematocrit, which can require venipuncture in order to treat, and exacerbation of sleep apnea. Gynecomastia and breast tenderness may occur with high dosages of testosterone due to peripheral conversion of testosterone by aromatase into excessive amounts of the estrogen estradiol. Many bodybuilders share this experience. Keep testosterone vials in a cool, dry place. This step keeps your dose steady and safe. Subcutaneous injections deliver testosterone into the fatty tissue layer just beneath the skin, rather than into muscle. Intramuscular injections deliver testosterone cypionate directly into muscle tissue. However, subcutaneous injections have gained significant traction in recent years, offering patients a potentially more comfortable alternative with comparable results. For decades, intramuscular injections were the standard for testosterone cypionate delivery. Read these subcutaneous injection instructions to make sure you understand how to administer your medication correctly. Smaller needles lead to more painless injections, but larger gauges can be necessary for a variety of reasons. Additionally, advertising from drug companies selling testosterone and human growth hormone, as well as dietary supplement companies selling all kinds of "boosters" for aging men, have emphasized the "need" of middle-aged or ageing men for testosterone. Shortly thereafter, in 1937, testosterone first became commercially available as a pharmaceutical drug in the form of pellets and then in ester form for intramuscular injection as the relatively short-acting testosterone propionate. Unlike testosterone ester and ether prodrugs however, these prohormones are only weakly androgenic/anabolic. In addition to ester and ether prodrugs, androgen prohormones or precursors of testosterone, such as dehydroepiandrosterone (DHEA), androstenediol, and androstenedione, exist as well, and convert into testosterone to variable extents upon oral ingestion. These metabolites, along with estradiol, may be involved in a number of the effects of testosterone in the brain, including its antidepressant, anxiolytic, stress-relieving, rewarding, and pro-sexual effects. In contrast to the case of testosterone, such potentiation occurs to a reduced extent or not at all with most synthetic AAS (as well as with DHT), and this is primarily responsible for the dissociation of anabolic and androgenic effects with these agents. Antiandrogens like cyproterone acetate, spironolactone, and bicalutamide can block the androgenic and anabolic effects of testosterone. In accordance, men experience sexual dysfunction at testosterone levels of below 300 ng/dL, and men that have levels of testosterone of approximately 200 ng/dL frequently experience such problems. Although testosterone has been found to be effective at improving sexual function in postmenopausal women, the doses employed have been supraphysiological. Testosterone therapy is effective in the short-term for the treatment of hypoactive sexual desire disorder (HSDD) in women. The United States Food and Drug Administration (FDA) stated in 2015 that neither the benefits nor the safety of testosterone supplement have been established for low testosterone levels due to aging. Similar to IM injections, periodic monitoring of the patients for risks and benefits should continue as recommended by clinical practice guidelines (1). Patients should be informed that currently, data and experience with SC testosterone therapy both are limited.
