Clearance has been shown from population pharmacokinetic studies to decrease significantly with age, increased alpha1 acid glycoprotein and albumin concentrations and decreased body surface area.Renal impairment is unlikely to affect metabolism or excretion of docetaxel as renal excretion contributes less than 5% of elimination. Limited data is available for docetaxel use in children with dosage between 55 and 75 mg/m2. Two paediatric studies have taken place that show a mean clearance of 33 L/h/m2 and concentration-time profiles best fitted by a two-compartmental model of distribution and elimination. Mean distribution half-life was 0.09 hours and mean elimination half-life was 1.4 hours in paediatric studies.Biodistribution of 14C-labelled docetaxel in three patients showed the bulk of the drug to be metabolised and excreted in bile to the faeces. Of the radioactively labelled docetaxel administered, 80% was eliminated to the faeces with 5% in the urine over seven days, an indication that urinary excretion of docetaxel is minimal. Saliva contributed minimal excretion and no excretion was detected through pulmonary means. The terminal half-life of docetaxel was determined as approximately 86 hours, through prolonged plasma sampling, contrary to the clinically stated terminal half-life of 10–18 hours. Mechanism of action
Molecular target
Docetaxel binds to microtubules reversibly with high affinity and has a maximum stoichiometry of 1 mole docetaxel per mole tubulin in microtubules. This binding stabilizes microtubules and prevents depolymerisation from calcium ions, decreased temperature and dilution, preferentially at the plus end of the microtubule.
Uses
Medical
Methyltestosterone is or has been used in the treatment of delayed puberty, hypogonadism, cryptorchidism, and erectile dysfunction in males, and in low doses to treat menopausal symptoms (specifically for osteoporosis, hot flashes, and to increase libido and energy), postpartum breast pain and engorgement, and breast cancer in women. It is specifically approved in the United States for the treatment of hypogonadism and delayed puberty in males and the treatment of advanced inoperable breast cancer in females. It was also approved in low doses in combination with esterified estrogens for the treatment of moderate to severe vasomotor symptoms associated with menopause in women in the United States, but this formulation was discontinued and hence is no longer used.Methyltestosterone is less effective in inducing masculinization than testosterone, but is useful for maintaining established masculinization in adults.The dosages of methyltestosterone used are 10 to 50 mg/day in men for common medical uses like hypogonadism and delayed puberty as well as physique- and performance-enhancing purposes and 2.5 mg/day in women for menopausal symptoms. Higher dosages of 50 to 200 mg/day have been used to treat women with inoperable breast cancer that has failed to respond to other therapies, although such dosages are associated with severe irreversible virilization. Non-medical
Methyltestosterone is used for physique- and performance-enhancing purposes by competitive athletes, bodybuilders, and powerlifters, although it is not commonly used relative to other AAS for such purposes. Available forms
Methyltestosterone is typically used as an oral medication.