Pharmacology: Pharmacodynamics: Cyproterone acetate is a competitive antagonist on the androgen receptor, has inhibitory effects on the androgen synthesis in target cells and produces a decrease of the androgen blood concentration through an antigonadotropic effect. This antigonadotropic effect is amplified by ethinylestradiol which up-regulates the synthesis of sexual hormone binding globulin (SHBG) in plasma. It thereby reduces free, biologically-available androgen in the circulation.
Pharmacokinetics: Cyproterone Acetate: Absorption: Orally administered cyproterone acetate is rapidly and completely absorbed. Peak serum concentrations of 15 ng/mL are reached at about 1.6 hrs after single ingestion. Bioavailability is about 88%.
Distribution: Cyproterone acetate is almost exclusively bound to serum albumin. Only 3.5-4% of the total serum drug concentrations are present as free steroid. The ethinylestradiol-induced increase in SHBG does not influence the serum protein binding of cyproterone acetate. The apparent volume of distribution of cyproterone acetate is about 986±437 L.
Metabolism: Cyproterone acetate is almost completely metabolized. The main metabolite in plasma was identified as 15β-OH-CPA which is formed via the cytochrome P-450 enzyme CYP3A4. The clearance rate from serum is about 3.6 mL/min/kg.
Elimination: Cyproterone acetate serum levels decrease in 2 phases which are characterized by half-lives of about 0.8 hr and about 2.3-3.3 days. Cyproterone acetate is partly excreted in unchanged form. Its metabolites are excreted at a urinary to biliary ratio of about 1:2. The half-life of metabolite excretion is about 1.8 days.
Steady-State Conditions: Cyproterone acetate pharmacokinetics are not influenced by SHBG levels. Following daily ingestion, drug serum levels increase by about 2.5-fold reaching steady-state conditions during the 2nd half of a treatment cycle.
Ethinylestradiol: Absorption: Orally administered ethinylestradiol is rapidly and completely absorbed. Peak serum concentrations of about 71 pg/mL are reached at 1.6 hrs. During absorption and first-liver passage, ethinylestradiol is metabolized extensively, resulting in a mean oral bioavailability of about 45% with a large interindividual variation of about 20-65%.
Distribution: Ethinylestradiol is highly but nonspecifically bound to serum albumin (approximately 98%) and induces an increase in the serum concentrations of SHBG. An apparent volume of distribution of about 2.8-8.6 L/kg was determined.
Metabolism: Ethinylestradiol is subject to presystemic conjugation in both small bowel mucosa and the liver. Ethinylestradiol is primarily metabolized by aromatic hydroxylation, but a wide variety of hydroxylated and methylated metabolites are formed, and these are present as free metabolites and as conjugates with glucuronides and sulfate. The clearance rate was reported to be about 2.3-7 mL/min/kg.
Elimination: Ethinylestradiol serum levels decrease in 2 disposition phases characterized by half-lives of about 1 hr and 10-20 hrs, respectively. Unchanged drug is not excreted, ethinylestradiol metabolites are excreted at a urinary to biliary ratio of 4:6. The half-life of metabolite excretion is about 1 day.
Steady-State Conditions: Steady state conditions are reached during the 2nd half of a treatment cycle when serum drug levels are higher by 60% as compared to single dose.
Toxicology: Preclinical Safety Data: Ethinylestradiol: The toxicity profile of ethinylestradiol is well-known. There are no preclinical data of relevance to the prescriber that provide additional safety information.
Cyproterone Acetate: Systemic Toxicity: Preclinical data reveal no specific risk for humans based on conventional studies of repeated dose toxicity.
Embryotoxicity/Teratogenicity: Investigations into embryotoxicity using the combination of the 2 active ingredients showed no effects indicative of a teratogenic effect following treatment during organogenesis before development of the external genital organs.
Administration of cyproterone acetate during the hormone-sensitive differentiation phase of the genital organs led to signs of feminization in male fetuses following higher doses. Observation of male newborn children who had been exposed in utero to cyproterone acetate did not show any signs of feminization. However, pregnancy is a contraindication for the use of Diane-35.
Genotoxicity and Carcinogenicity: Recognized 1st-line tests of genotoxicity gave negative results when conducted with cyproterone acetate. However, further tests showed that cyproterone acetate was capable of producing adducts with DNA (and an increase in DNA repair activity) in liver cells from rats and monkeys and also in freshly isolated human hepatocytes, the DNA-adduct level in dog liver cells was extremely low.
This DNA adduct formation occurred at systemic exposures that might be expected to occur in the recommended dose regimens for cyproterone acetate. In vivo consequences of cyproterone acetate treatment were the increased incidence of focal, possibly pre-neoplastic liver lesions in which cellular enzymes were altered in female rats and an increase of mutation frequency in transgenic rats carrying a bacterial gene as target for mutations.
Clinical experience and well-conducted epidemiological trials to date would not support an increased incidence of hepatic tumors in man. Nor did investigations into the tumorigenicity of cyproterone acetate in rodents reveal any indication of a specific tumorigenic potential.
However, it must be borne in mind that sexual steroids can promote the growth of certain hormone-dependent tissues and tumors.
On the whole, the available findings do not raise any objection to the use of Diane-35 in humans if used in accordance with the directions for the given indication and at the recommended dose.