Testosterone Propionate

Testosterone was the first successfully synthesized anabolic steroid. Testosterone propionate is a fast-acting, short-ester, oil-based injectable testosterone compound that is commonly prescribed for the treatment of hypogonadism – low testosterone levels and various related symptoms in males.

Testosterone propionate was first described in 1935 to increase synthetic testosterone’s therapeutic usefulness by slowing its release into the bloodstream. It was released for clinical use two years later by Schering AG in Germany, featured in a hybrid blend with testosterone enanthate under the brand name Testoviron. This was also the first commercially available version on the U.S. prescription drug market and remained the dominant form of testosterone globally prior to 1960.

Testosterone

Testosterone is the primary androgen found in the body. Endogenous testosterone is synthesized by cells in the testis, ovary, and adrenal cortex. Therapeutically, testosterone is used in the management of hypogonadism, either congenital or acquired. Testosterone is also the most effective exogenous androgen for the palliative treatment of carcinoma of the breast in postmenopausal women. Testosterone was in use in 1938 and approved by the FDA in 1939. Anabolic steroids, derivatives of testosterone, have been used illicitly and are now controlled substances. Testosterone, like many anabolic steroids, was classified as a controlled substance in 1991. Testosterone is administered parenterally in regular and delayed-release (depot) dosage forms. In September 1995, the FDA initially approved testosterone transdermal patches (Androderm); many transdermal forms and brands are now available including implants, gels, and topical solutions. A testosterone buccal system, Striant, was FDA approved in July 2003; the system is a mucoadhesive product that adheres to the buccal mucosa and provides a controlled and sustained release of testosterone. In May 2014, the FDA approved an intranasal gel formulation (Natesto). A transdermal patch (Intrinsa) for hormone replacement in women is under investigation; the daily dosages used in women are much lower than for products used in males. The FDA ruled in late 2004 that it would delay the approval of Intrinsa women’s testosterone patch and has required more data regarding safety, especially in relation to cardiovascular and breast health.

The Propionate Ester: An ester is any of a class of organic compounds that react with water to produce alcohols and organic or inorganic acids. Most esters are derived from carboxylic acids, and injectable testosterone is typically administered along with one or multiple esters. The addition of a carbon chain (ester) attached to the testosterone molecule controls how soluble it will be once it’s inside the bloodstream. The larger the carbon chain, the longer the ester, and the less soluble the medication; a large/long ester will have a longer half-life. The inverse is true of short carbon chains, like the propionate ester, which acts rapidly upon the body and evacuates the body at a similar rate. With a three-carbon chain, the testosterone ester possesses the shortest half life of all testosterone esters at 4 days.

Mechanism of Action

Endogenous testosterone is responsible for sexual maturation at all stages of development throughout life. Synthetically, it is prepared from cholesterol. The function of androgens in male development begins in the fetus, is crucial during puberty, and continues to play an important role in the adult male. Women also secrete small amounts of testosterone from the ovaries. The secretion of androgens from the adrenal cortex is insufficient to maintain male sexuality.

Increased androgen plasma concentrations suppress gonadotropin-releasing hormone (reducing endogenous testosterone), luteinizing hormone, and follicle-stimulating hormone by a negative-feedback mechanism. Testosterone also affects the formation of erythropoietin, the balance of calcium, and blood glucose. Androgens have a high lipid solubility, enabling them to rapidly enter cells of target tissues. Within the cells, testosterone undergoes enzymatic conversion to 5-alpha-dihydrotestosterone and forms a loosely bound complex with cystolic receptors. Androgen action arises from the initiation of transcription and cellular changes in the nucleus brought about by this steroid-receptor complex.

Normally, endogenous androgens stimulate RNA polymerase, resulting in an increased protein production.These proteins are responsible for normal male sexual development, including the growth and maturation of the prostate, seminal vesicle, penis, and scrotum. During puberty, androgens cause a sudden increase in growth and development of muscle, with redistribution of body fat. Changes also take place in the larynx and vocal cords, deepening the voice. Puberty is completed with beard development and growth of body hair. Fusion of the epiphyses and termination of growth is also governed by the androgens, as is the maintenance of spermatogenesis. When endogenous androgens are unavailable, use of exogenous androgens are necessary for normal male growth and development.

Mechanism of Action

Pharmacokinetics

Testosterone is administered intramuscularly (IM); via subcutaneous injection; to the skin as a topical gel, solution, ointment or transdermal systems for transdermal absorption; by implantation of long-acting pellets, or; via buccal systems.

In serum, testosterone is bound to protein. It has a high affinity for sex hormone binding globulin (SHBG) and a low affinity for albumin. The albumin-bound portion freely dissociates. The affinity for SHBG changes throughout life. It is high during prepuberty, declines during adolescence and adult life, then rises again in old age. The active metabolite DHT has a greater affinity for SHBG than testosterone. Elimination half-life is 10—100 minutes and is dependent on the amount of free testosterone in the plasma.

Testosterone is metabolized primarily in the liver to various 17-keto steroids. It is a substrate for hepatic cytochrome P450 (CYP) 3A4 isoenzyme.1 Estradiol and dihydrotestosterone (DHT) are the major active metabolites, and DHT undergoes further metabolism. Testosterone activity appears to depend on formation of DHT, which binds to cytosol receptor proteins. Further metabolism of DHT takes place in reproductive tissues. About 90% of an intramuscular testosterone dose is excreted in the urine as conjugates of glucuronic and sulfuric acids. About 6% is excreted in the feces, largely unconjugated. There is considerable variation in the half-life of testosterone as reported in the literature, ranging from 10 to 100 minutes.

Affected cytochrome P450 isoenzymes and drug transporters: CYP3A4, P-gp

Testosterone is a substrate for CYP3A4 and is also both transported by and an inhibitor of P-glycoprotein (P-gp) transport.

Route-Specific Pharmacokinetics:

Intramuscular Route: Parenteral testosterone formulations have been developed that reduce the rate of testosterone secretion, with esters being less polar and slowly absorbed from intramuscular sites. Esters have a duration of action of 2—4 weeks following IM administration. The esters are hydrolyzed to free testosterone, which is inactivated in the liver.

Possible interactions include: certain medicines for diabetes; certain medicines that treat or prevent blood clots like warfarin; oxyphenbutazone; propranolol; steroid medicines like prednisone or cortisone. This list may not describe all possible interactions.

Interactions

NOTE: Testosterone is a substrate for hepatic cytochrome P450 (CYP) 3A4 isoenzyme. Testosterone is also both transported by and an inhibitor of P-glycoprotein transport.

Testosterone can increase the anticoagulant action of warfarin. Serious bleeding has been reported in some patients with this drug-drug interaction. Although the mechanism is unclear, testosterone may reduce procoagulant factors. Reduction of warfarin dosage may be necessary if testosterone therapy is coadministered. More frequent monitoring of INR and prothrombin time in patients taking such oral anticoagulants is recommneded, especially at the initiation and termination of androgen therapy. It is unclear if testosterone can augment the anticoagulant response to heparin therapy or if testosterone alters the effect of other non-coumarin oral anticoagulants in a similar manner.

Based on case reports with methyltestosterone and danazol, androgens may increase plasma concentrations of cyclosporine, leading to a greater risk of nephrotoxicity.

Coadministration of corticosteroids and testoterone may increase the risk of edema, especially in patients with underlying cardiac or hepatic disease. Corticosteroids with greater mineralocorticoid activity, such as fludrocortisone, may be more likely to cause edema. Administer these drugs in combination with caution.

Goserelin and leuprolide inhibit steroidogenesis. Concomitant use of androgens with goserelin or leuprolide is relatively contraindicated and would defeat the purpose of goserelin or leuprolide therapy.

Androgens can increase the risk of hepatotoxicity and therefore should be used with caution when administered concomitantly with other hepatotoxic medications. Patients should be monitored closely for signs of liver damage, especially those with a history of liver disease.

Androgens may be necessary to assist in the growth response to human growth hormone, but excessive doses of androgens in prepubescent males can accelerate epiphyseal maturation.

The antiandrogenic effects of the 5-alpha reductase inhibitors (i.e., dutasteride, finasteride) are antagonistic to the actions of androgens; it would be illogical for patients taking androgens to use these antiandrogenic drugs.

Androgens are known to stimulate erythropoiesis. Despite the fact that endogenous generation of erythropoietin is depressed in patients with chronic renal failure, other tissues besides the kidney can synthesize erythropoietin, albeit in small amounts. Concurrent administration of androgens can increase the patient’s response to epoetin alfa, reducing the amount required to treat anemia. Because adverse reactions have been associated with an abrupt increase in blood viscosity, this drug combination should be avoided, if possible. Further evaluation of this combination needs to be made.

Drug interactions with Saw palmetto, Serenoa repens have not been specifically studied or reported. Saw palmetto extracts appear to have antiandrogenic effects. The antiandrogenic effects of Saw palmetto, Serenoa repens would be expected to antagonize the actions of androgens; it would seem illogical for patients taking androgens to use this herbal supplement.

Limited data suggest that testosterone concentrations increase during fluconazole administration. It appears that fluconazole doses of 200 mg/day or greater are more likely to produce this effect than doses of 25—50 mg/day. The clinical significance of this interaction is unclear at this time. Although data are not available, a similar reaction may occur with voriconazole. Both fluconazole and voriconazole are inhibitors of CYP3A4, the hepatic microsomal isoenzyme responsible for metabolism of testosterone.

Exogenously administered androgens (testosterone derivatives or anabolic steroids) have variable effects on blood glucose control in patients with diabetes mellitus. In general, low testosterone concentrations are associated with insulin resistance. Further, when hypogonadal men (with or without diabetes) are administered exogenous androgens, glycemic control typically improves as indicated by significant reductions in fasting plasma glucose concentrations and HbA1c. In one study in men with diabetes, testosterone undecenoate 120 mg PO/day for 3 months decreased HbA1c concentrations from a baseline of 10.4% to 8.6% (p < 0.05); fasting plasma glucose concentrations decreased from 8 mmol/l at baseline to 6 mmol/l (p < 0.05). Significant reductions in HbA1c and fasting plasma glucose concentrations did not occur in patients taking placebo. Similar results have been demonstrated with intramuscular testosterone 200 mg administered every 2 weeks for 3 months in hypogonadal men with diabetes. In healthy men, testosterone enanthate 300 mg IM/week for 6 weeks or nandrolone 300 mg/week IM for 6 weeks did not adversely affect glycemic control; however, nandrolone improved non-insulin mediated glucose disposal. It should be noted that some studies have shown that testosterone supplementation in hypogonadal men has no effect on glycemic control. Conversely, the administration of large doses of anabolic steroids in power lifters decreased glucose tolerance, possibly through inducing insulin resistance. While data are conflicting, it would be prudent to monitor all patients with type 2 diabetes on antidiabetic agents receiving androgens for changes in glycemic control, regardless of endogenous testosterone concentrations. Hypoglycemia or hyperglycemia can occur; dosage adjustments of the antidiabetic agent may be necessary.

In vitro, both genistein and daidzein inhibit 5 alpha-reductase isoenzyme II, resulting in decreased conversion of testosterone to the potent androgen 5-alpha-dihydrotestosterone (DHT) and a subsequent reduction in testosterone-dependent tissue proliferation. The action is similar to that of finasteride, but is thought to be less potent. Theoretically, because the soy isoflavones appear to inhibit type II 5-alpha-reductase, the soy isoflavones may counteract the activity of the androgens.

Interactions

Conivaptan is a potent inhibitor of CYP3A4 and may increase plasma concentrations of drugs that are primarily metabolized by CYP3A4. Testosterone is a substrate for CYP3A4 isoenzymes. The clinical significance of this theoretical interaction is not known.

Testosterone is an inhibitor of P-glycoprotein transport. Ranolazine is a substrate of P-glycoprotein, and inhibitors of P-glycoprotein may increase the absorption of ranolazine. In addition, ranolazine inhibits CYP3A and may increase plasma concentrations of drugs that are primarily metabolized by CYP3A4 such as testosterone.

Ambrisentan is a substrate for P-glycoprotein transport, an energy-dependent drug efflux pump. The inhibition of P-glycoprotein, by drugs such as testosterone, may lead to a decrease in the intestinal metabolism and an increase in the oral absorption of ambrisentan. If ambrisentan is coadministered with a P-glycoprotein inhibitor, patients should be monitored closely for adverse effects.

Coadministration of oxyphenbutazone and testosterone may lead to elevated concentrations of oxyphenbutazone. Monitor patients for adverse effects when coadministering these drugs together.

Testosterone cypionate has been shown to increase the clearance of propranolol in one study. Monitor patients taking testosterone and propranolol together for decreased therapeutic efficacy of propranolol.

Coadministration of dabigatran and testosterone may result in increased dabigatran serum concentrations, and, therefore, an increased risk of adverse effects. Coadministration of dabigatran and testosterone should be avoided in patients with severe renal impairment (CrCl 15—30 ml/min). Dabigatran is a substrate of P-gp; testosterone is a P-gp inhibitor. P-gp inhibition and renal impairment are the major independent factors that result in increased exposure to dabigatran.

Concomitant use of testosterone, a P-glycoprotein (P-gp) inhibitor, and afatinib, a P-gp substrate, may increase the exposure of afatinib. If the use of both agents is necessary, consider reducing the afatinib dose if the original dose is not tolerated.

Concomitant use of intranasal testosterone (e.g., Natesto) and other intranasally administered drugs in not recommended; the drug interaction potential between these agents is unknown. Eighteen males with seasonal allergic rhinitis were treated with intranasal testosterone and randomized to receive oxymetazoline (30 minutes prior to intranasal testosterone) or no treatment. In general, serum total testosterone concentrations were decreased by 21—24% in males with symptomatic allergic rhinitis, due to the underlying condition. A mean decrease in AUC and Cmax (2.6% and 3.6%, respectively) for total testosterone was observed in males with symptomatic seasonal rhinitis when treated with oxymetazoline compared to untreated patients. Concomitant use of oxymetazoline does not impact the absorption of testosterone.

This list may not include all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.

Storage

Store this medication at 68°F to 77°F (20°C to 25°C) and away from heat, moisture and light. Keep all medicine out of the reach of children. Throw away any unused medicine after the beyond use date. Do not flush unused medications or pour down a sink or drain. NOTE: Warming and shaking the vial should redissolve any crystals that may have formed during storage temperatures lower than recommended.