The therapeutically useful androgens are synthetic derivatives of naturally occurring testosterone. They include:
· testosterone enanthate
· testosterone propionate.
The pharmacokinetic properties of therapeutic androgens resem-ble those of naturally occurring testosterone.
The oral androgens—fluoxymesterone and testolactone—are well absorbed. The parenteral ones—testosterone enanthate and testosterone propionate—are designed specifically for slow ab-sorption after I.M. injection.
Androgens are well distributed throughout the body, metabolized extensively in the liver, and excreted in urine.
The duration of the parenteral forms is longer because the oil sus-pension is absorbed slowly. Parenteral androgens are adminis-tered one to three times per week.
Androgens probably act by one or more mechanisms. They may reduce the number of prolactin receptors or may bind competi-tively to those that are available.
Androgens may inhibit estrogen synthesis or competitively bind at estrogen receptors. These actions prevent estrogen from affect-ing estrogen-sensitive tumors.
Androgens are indicated for the palliative treatment of advanced breast cancer, particularly in postmenopausal women with bone metastasis.
Androgens may alter dose requirement in patients receiving in-sulin, oral antidiabetic drugs, or oral anticoagulants. Taking them with drugs that are toxic to the liver increases the risk of liver tox-icity. (See Adverse reactions to androgens.)