Fluoxymesterone/Halotestin Introduction Fluoxymesterone, sold under the brand names Halotestin and Ultandren among others, is an androgen and anabolic steroid (AAS) medication which is used in the treatment of low testosterone levels in men, delayed puberty in boys, breast cancer in women, and anemia. It is taken by mouth. Fluoxymesterone was first described in 1956 and was introduced for medical use in 1957. In addition to its medical use, fluoxymesterone is used to improve physique and performance. The drug is a controlled substance in many countries and so non-medical use is generally illicit. As an AAS, fluoxymesterone is an agonist of the androgen receptor (AR), similarly to androgens like testosterone and DHT. It is a substrate for 5 α -reductase like testosterone, and so is potentiated in so-called "androgenic" tissues like the skin, hair follicles, and prostate gland via transformation into 5α-dihydrofluoxymesterone. As such, fluoxymesterone has a relatively poor ratio of anabolic to androgenic activity similarly to testosterone and methyltestosterone. Fluoxymesterone has been reported to be non-aromatizable due to steric hindrance by its C11β hydroxyl group, and hence is not considered to have a propensity for producing estrogenic effects such as gynecomastia or fluid retention. However, paradoxically, a case report of severe fluoxymesterone-induced gynecomastia exists, and gynecomastia associated with fluoxymesterone has also been reported in other publications, although this may not be due to estrogenic activity. Fluoxymesterone is thought to possess little or no progestogenic activity. Because of the presence of its 17 α -methyl group, the metabolism of fluoxymesterone is impeded, resulting in it being orally active, although also hepatotoxic. Fluoxymesterone has approximately 80% oral bioavailability, unlike testosterone, as the C17 α methyl group of fluoxymesterone inhibits first-pass metabolism. It has very low affinity for human serum sex hormone-binding globulin (SHBG), less than 5% of that of testosterone and less than 1% of that of DHT. The drug is metabolized in the liver, mainly by 6β-hydroxylation, 5 αand 5β-reduction, 3α- and 3β-keto-oxidation, and 11β-hydroxy-oxidation. Its known active metabolites include 5 α -dihydrofluoxymesterone and 11-oxofluoxymesterone. Fluoxymesterone has an elimination half-life of approximately 9.2 hours, which is long relative to that of testosterone. It is eliminated in the urine, with less than 5% excreted unchanged. In a test for halotestin, a dry residue obtained from a urine sample is dissolved in dimethylformamide and a sulfur trioxide-pyridine complex and is heated with 1% potassium carbonate solution. Halotestin and many of its metabolites contain two polar hydroxyl groups, leading to intermolecular hydrogen bonding that increases their boiling point and reduces volatility. In order to attain a gaseous sample for GC-MS, the products of hydrolysis are extracted, dissolved in methanol and derivatised to form volatile trimethylsilyl (TMS) esters by adding 1
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