formestane formestane formestane, formerly sold under the brand name lentaron among others, is a steroidal, selective aromatase inhibitor which is used in the treatment of estrogen receptor-positive breast cancer in postmenopausal women. the drug is not active orally, and was available only as an intramuscular depot injection. formestane was not approved by the united states fda and the injectable form that was used in europe in the past has been withdrawn from the market. formestane is an analogue of androstenedione. formestaneclinical datatrade nameslentaron, othersother names4-hydroxyandrost-4-ene-3,17-dioneahfs/drugs.cominternational drug namesroutes ofadministrationintramuscular injectiondrug classaromatase inhibitor; antiestrogenatc codel02bg02 (who) identifiers iupac name (8r,9s,10r,13s,14s)-4-hydroxy-10,13-dimethyl-2,6,7,8,9,11,12,14,15,16-decahydro-1h-cyclopentaphenanthrene-3,17-dione cas number566-48-3 ypubchem cid11273chemspider10799 yuniipub9t8t355keggd07260 ychebichebi:75172 nchemblchembl132530 ycomptox dashboard (epa)dtxsid3034113 echa infocard100.153.838 chemical and physical dataformulac19h26o3molar mass302.414 g·mol−13d model (jsmol)interactive image smiles o=c4c(/o)=c3/cc2(cc1(c(=o)cc12)c)3(c)cc4 inchi inchi=1s/c19h26o3/c1-18-10-8-15(20)17(22)14(18)4-3-11-12-5-6-16(21)19(12,2)9-7-13(11)18/h11-13,22h,3-10h2,1-2h3/t11-,12-,13-,18+,19-/m0/s1 ykey:osvmtwjcgufaod-kzqroqtasa-n y ny (what is this?) (verify) formestane is often used to suppress the production of estrogens from anabolic steroids or prohormones. it also acts as a prohormone to 4-hydroxytestosterone, an active steroid which displays weak androgenic activity in addition to acting as a weak aromatase inhibitor. pharmacodynamics of aromatase inhibitors generationmedicationdosage % inhibitionaclassbic50c firsttestolactone250 mg 4x/day p.o. ?type i ? 100 mg 3x/week i.m. ? rogletimide200 mg 2x/day p.o.400 mg 2x/day p.o.800 mg 2x/day p.o.50.6%63.5%73.8%type ii ? aminoglutethimide250 mg mg 4x/day p.o.90.6%type ii4,500 nm secondformestane125 mg 1x/day p.o.125 mg 2x/day p.o.250 mg 1x/day p.o.72.3%70.0%57.3%type i30 nm 250 mg 1x/2 weeks i.m.500 mg 1x/2 weeks i.m.500 mg 1x/1 week i.m.84.8%91.9%92.5% fadrozole1 mg 1x/day p.o.2 mg 2x/day p.o.82.4%92.6%type ii ? thirdexemestane25 mg 1x/day p.o.97.9%type i15 nm anastrozole1 mg 1x/day p.o.10 mg 1x/day p.o.96.7–97.3%98.1%type ii10 nm letrozole0.5 mg 1x/day p.o.2.5 mg 1x/day p.o.98.4%98.9%–>99.1%type ii2.5 nm footnotes: a = in postmenopausal women. b = type i: steroidal, irreversible (substrate-binding site). type ii: nonsteroidal, reversible (binding to and interference with the cytochrome p450 heme moiety). c = in breast cancer homogenates. sources: see template.