Lentaron — formestane

Formestane is classified as a selective irreversible steroidal aromatase inhibitor. This agent is structurally a derivative of androstenedione, differing from this well known prohormone only by the addition of a 4-hydroxyl group. This group, however, is responsible for causing an irreversible attachment between formestane and aromatase when the two come into contact with each other. This means that formestane will bond with the enzyme and never let it go, permanently deactivating it as a result. The enzyme will need to be replaced, through normal attrition, before the body will recover its lost estrogen synthesizing capacity. This may take several days or more following cessation of therapy. Given this mode of action, formestane is also referred to as a “suicide” aromatase inhibitor, as the drug essentially sacrifices itself in the process of blocking estrogen conversion. As a class of drugs, aromatase inhibitors are used (off-label) by male bodybuilders and athletes to prevent the estrogenic side effects of certain anabolic/androgenic steroids, and to increase fat loss and muscle definition while dieting.

Because of its potent estrogen-suppressing action, formestane has been used clinically to treat breast cancer patients in a number of countries including England, Germany, Switzerland, Spain, Australia, New Zealand, Italy, and Malaysia. It has been shown to be an effective option as a second line of defense after tamoxifen, an estrogen receptor antagonist, has failed to elicit a positive response with patients, and produces an overall response statistically similar to tamoxifen when administered as the first-line therapy. In terms of overall potency, formestane is not as strong as the selective third generation inhibitors likeArimidex (anastrozole) orFemara (letrozole). One study, for example, notes a 79% level of suppression of estrogen levels with 4 weeks use ofArimidex 1 mg daily (on par with levels noted withFemara use), but only a 58% level of suppression with intramuscular formestane injections (250 mg every two weeks). But next to estrogen receptor antagonists likeClomid (clomiphene citrate) andNolvadex (tamoxifen citrate), formestane is significantly more effective at blocking the effects of estrogen in the body.

Brand name Lentaron, Formestane, Lentaron depot

Formestane History

Formestane was the first selective aromatase inhibitor to be developed as a prescription drug, first appearing in Europe during the mid-1990s under the Lentaron Depot brand name. It was sold by Novartis, which marketed Lentaron Depot in two-dozen countries including Argentina, Austria, Belgium, Brazil, Canada, Chile, Czech Republic, Denmark, France, Germany, Greece, Hong Kong, Ireland, Israel, Italy, Malaysia, Netherlands, Portugal, South Africa, Spain, Switzerland, Turkey, and the United Kingdom. With the emergence of newer and more effective aromatase inhibitors, however, formestane soon lost market presence at a rapid rate. Most of the initial Lentaron Depot preparations have since been discontinued. The drug remains available today, but only in a small number of nations. This includes Austria, Brazil, Czech Republic, Hong Kong, and Turkey.

How is Formestane Supplied

Formestane is most commonly supplied in a sterile solution containing 125 mg/mL of drug in a 2 mL ampule.

Structural Characteristics of Formestane

Formestane is classified a steroidal selective irreversible aromatase inhibitor. It has the chemical designation 4- Hydroxyandrost-4-ene-3,17-dione.

Formestane Side Effects

Common side effects associated with the use of an aromatase inhibitor include hot flashes, joint pain, weakness, fatigue, mood changes, depression, high blood pressure, swelling of the arms/legs, and headache. Aromatase inhibitors may also decrease bone mineral density, which may lead to osteoporosis and an increase in fractures in susceptible patients. Some individuals may also respond to the medication with gastrointestinal side effects including nausea and vomiting. Aromatase inhibitors can harm the development of an unborn fetus, and should never be taken or handled during pregnancy. When taken by men (as an off-label use) to reduce estrogenicity during prolonged periods of steroid treatment, aromatase inhibitors may increase cardiovascular disease (CVD) risk by retarding some beneficial properties of estrogen on cholesterol values. Studies have demonstrated that when an aromatizable steroid such as testosterone enanthate is taken in conjunction with an aromatase inhibitor, suppression of HDL (good) cholesterol levels becomes significantly more pronounced. Since the estrogen receptor agonist/antagonist Nolvadex generally does not display the same anti-estrogenic (negative) effect on cholesterol values, it is usually favored over aromatase inhibitors for estrogen maintenance by male bodybuilders and athletes concerned with cardiovascular health.

Formestane Administration

Formestane is indicated for the treatment of advanced breast cancer in postmenopausal women. The recommended dosage is 250 mg by intramuscular injection (buttock) every two weeks. Although not a medically approved form of the drug, studies have demonstrated that a similar level of estrogen suppression can also be achieved with oral use of formestane. Due to poor bioavailability, however, the dose needed is around 250 mg per day . When used (off-label) to mitigate the estrogenic side effects of anabolic/androgenic steroid use or increase muscle definition, male athletes and bodybuilders often take 250 mg every two weeks by injection, or 250 mg per day orally.

Formestane Availability

Formestane is not widely available as a prescription drug, and consequently is rarely circulated in the athletic community.

Newbies Research Guide reference

Formestane is the first in a new line of selective, steroidal-based aromatase inhibitors. It is currently available in a few European countries, and is expected to reach U.S. shelves before long. Formestane is structurally a derivative of androstenedione, most specifically 4-OH androstenedione. Androstenedione is a readi- ly aromatized steroid, so clearly this similarity welcomes interaction with the aromatase enzyme. Its activity in the body is in fact that of a suicide inhibitor, meaning that the compound will become inextricably bound to the aromatase enzyme upon contacting it. Its effect is therefore comparatively much more lasting than that seen with reversible, competitive inhibitors. This is no doubt the reason formestane was shown in studies to be as much as 60 times more potent than aminoglutethimide. As with Arimidex, this compound can help achieve near total suppression of aromatase.

Due to poor oral bioavailability, formestane is commercially prepared as an injectable product. The typical recommendation is an injection of 250mg (typically 1 ampule or injection) every two weeks. Though estrogen suppression can be marked with this dosing pattern, some studies do suggest that by the second week (near the time the dosage is to be repeated) estrogen levels may begin to recover. Although a more frequent schedule may provide more stable results, again cost is a prohibiting factor. I am looking at a current mail-order list in which a single 250mg ampule of formestane sells for $249. This would equate to a monthly expense of around $500, roughly twice the cost of the recommended anastrozole dose. It is of course also very doubtful that, with the high potency of this compound, an athlete would ever have trouble with the recommended schedule.


Wlliam Llewellyn (2011) - Anabolics
Newbies Research Guide

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