Clomifene


Clomifene, also known as clomiphene, is a medication used to treat infertility in women who do not ovulate. This includes those who have polycystic ovary syndrome. Use results in a greater chance of twins. It is taken by mouth once a day with a course of treatment generally lasting five days.
Common side effects include pelvic pain and hot flashes. Other side effects can include changes in vision, vomiting, trouble sleeping, ovarian cancer, and seizures. It is not recommended in people with liver disease, abnormal vaginal bleeding of unknown cause, or who are pregnant. Clomifene is in the selective estrogen receptor modulator family of medication and is a nonsteroidal medication. It works by causing the release of GnRH by the hypothalamus, and subsequently gonadotropin from the anterior pituitary.
Clomifene was approved for medical use in the United States in 1967. It is on the World Health Organization's List of Essential Medicines. Its introduction began the era of assisted reproductive technology.

Medical uses

Ovulation induction

Clomifene is one of several alternatives for ovulation induction in those who are infertile due to anovulation or oligoovulation. Evidence is lacking for the use of clomifene in those who are infertile without a known reason. In such cases, studies have observed a clinical pregnancy rate 5.6% per cycle with clomifene treatment vs. 1.3%–4.2% per cycle without treatment.
Proper timing of the drug is important; it should be taken starting on about the fifth day of the cycle, and there should be frequent intercourse.
The following procedures may be used to monitor induced cycles:
Repeat dosing: This 5-day treatment course can be repeated every 30 days. The dosage may be increased by 50-mg increments in subsequent cycles until ovulation is achieved. It is not recommended by the manufacturer to use clomifene for more than 6 cycles.
It is no longer recommended to perform an ultrasound examination to exclude any significant residual ovarian enlargement before each new treatment cycle.

Other uses

Clomifene has also been used with other assisted reproductive technology to increase success rates of these other modalities.
Clomifene is sometimes used in the treatment of male hypogonadism as an alternative to testosterone replacement therapy. The medication has been used at a dosage of 20 to 50 mg three times per week to once day for this indication. It has been found to increase testosterone levels by 2- to 2.5-times in hypogonadal men at such dosages. Despite the use of questionnaires in testosterone replacement comparator trials being called into question, clomifene's lower cost, therapeutic benefits, and greater value towards hypogonadism improvement have been noted.
Clomifene has been used in the treatment of gynecomastia. It has been found to be useful in the treatment of some cases of gynecomastia but it is not as effective as tamoxifen or raloxifene for this indication. It has shown variable results for gynecomastia and hence is not recommended for treatment of the condition.

Contraindications

Contraindications include an allergy to the medication, pregnancy, prior liver problems, abnormal vaginal bleeding of unclear cause, ovarian cysts other than those due to polycystic ovarian syndrome, unmanaged adrenal or thyroid problems, and pituitary tumors.

Side effects

The most common adverse drug reaction associated with the use of clomifene is reversible ovarian enlargement.
Less common effects include visual symptoms, headaches, vasomotor flushes, light sensitivity and pupil constriction, abnormal uterine bleeding and/or abdominal discomfort.
Rare adverse events include: high blood level of triglycerides, liver inflammation, reversible baldness and/or ovarian hyperstimulation syndrome.
Clomifene can lead to multiple ovulation, hence increasing the chance of twins and triplets.
Rates of birth defects and miscarriages do not appear to change with the use of clomifene for fertility. Clomifene has been associated with liver abnormalities and a couple of cases of hepatotoxicity.

Cancer risk

Some studies have suggested that clomifene if used for more than a year may increase the risk of ovarian cancer. This may only be the case in those who have never been and do not become pregnant. Subsequent studies have failed to support those findings.
Clomifene has been shown to be associated with an increased risk of malignant melanomas and thyroid cancer. Thyroid cancer risk was not associated with the number of pregnancies carried to viability.

Pharmacology

Pharmacodynamics

Selective estrogen receptor modulator activity

Clomifene is a nonsteroidal triphenylethylene derivative that acts as a selective estrogen receptor modulator. It consists of a racemic mixture of zuclomifene and enclomifene, each of which has unique pharmacologic properties. It is a mixed agonist and antagonist of the estrogen receptor. Clomifene activates the ERα in the setting of low baseline estrogen levels and partially blocks the receptor in the context of high baseline estrogen levels. Conversely, it is an antagonist of the ERβ. Clomifene is a long-acting ER ligand, with a nuclear retention of greater than 48 hours.
Even though clomifene has some estrogenic effect, the antiestrogenic property is believed to be the primary source for stimulating ovulation. Clomifene appears to act mostly in the hypothalamus where it depletes hypothalamic ERs and blocks the negative feedback effect of circulating endogenous estradiol, which in turn results in an increase in hypothalamic gonadotropin-releasing hormone pulse frequency and circulating concentrations of follicle-stimulating hormone and luteinizing hormone.
In normal physiologic female hormonal cycling, at 7 days past ovulation, high levels of estrogen and progesterone produced from the corpus luteum inhibit GnRH, FSH, and LH at the hypothalamus and anterior pituitary. If fertilization does not occur in the post-ovulation period the corpus luteum disintegrates due to a lack of human chorionic gonadotropin. This would normally be produced by the embryo in the effort of maintaining progesterone and estrogen levels during pregnancy.
Therapeutically, clomifene is given early in the menstrual cycle. It is typically prescribed beginning on day 3 and continuing for 5 days. By that time, FSH levels are rising steadily, causing the development of a few follicles. Follicles, in turn, produce the estrogen, which circulates in serum. In the presence of clomifene, the body perceives a low level of estrogen, similar to day 22 in the previous cycle. Since estrogen can no longer effectively exert negative feedback on the hypothalamus, GnRH secretion becomes more rapidly pulsatile, which results in increased pituitary gonadotropin release. Increased FSH levels cause the growth of more ovarian follicles, and subsequently rupture of follicles resulting in ovulation. Ovulation occurs most often 6 to 7 days after a course of clomifene.
Clomifene has antiestrogenic effects in the uterus. There is little clinical research on the influence of clomifene in many target tissues, such as lipids, the cardiovascular system, and the breasts. Positive effects of clomifene on bone have been observed. Clomifene has been found to decrease insulin-like growth factor 1 levels in women.
In normal men, 50 mg/day clomifene for 8 months has been found to increase testosterone levels by around 870 ng/dL in younger men and by around 490 ng/dL in elderly men. Estradiol levels increased by 62 pg/mL in younger men and by 40 pg/mL in elderly men. These findings suggest that the progonadotropic effects of clomifene are stronger in younger men than in older men. In men with hypogonadism, clomifene has been found to increase testosterone levels by 293 to 362 ng/dL and estradiol levels by 5.5 to 13 pg/mL. In a large clinical study of men with low testosterone levels, 25 mg/day clomifene increased testosterone levels from 309 ng/dL to 642 ng/dL after 3 months of therapy. No significant changes in HDL cholesterol, triglycerides, fasting glucose, or prolactin levels were observed, although total cholesterol levels decreased significantly.

Other activities

Clomifene is an inhibitor of the conversion of desmosterol into cholesterol by the enzyme 24-dehydrocholesterol reductase. Concerns about possible induction of desmosterolosis and associated symptoms such as cataracts and ichthyosis with extended exposure precluded the use of clomifene in the treatment of breast cancer. Continuous use of clomifene has been found to increase desmosterol levels by 10% and continuous high doses of clomifene have been reported to produce visual disturbances.

Pharmacokinetics

Clomifene produces N-desmethylclomifene, clomifenoxide, and 4-hydroxyclomifene as metabolites. Clomifene has an onset of action of 5 to 10 days following course of treatment and an elimination half-life about 5 days. Most clomifene metabolism occurs hepatically, where it undergoes enterohepatic recirculation. Clomifene and its metabolites are excreted primarily through feces, and excretion can occur up to 6 weeks after discontinuation.

Chemistry

Clomifene is a triphenylethylene derivative. It is a mixture of two geometric isomers, enclomifene and zuclomifene. These two isomers have been found to contribute to the mixed estrogenic and antiestrogenic properties of clomifene.

History

A team at William S. Merrell Chemical Company led by Frank Palopoli synthesized clomifene in 1956; after its biological activity was confirmed a patent was filed and issued in November 1959. Scientists at Merrell had previously synthesized chlorotrianisene and ethamoxytriphetol. Clomifene was studied in the treatment of advanced breast cancer during the period of 1964 to 1974 and was found to be effective but was abandoned due to concerns about desmosterolosis with extended use. Short-term use did not raise the same concerns however and clomifene continued to be studied for other indications.
Clinical studies were conducted under an Investigational New Drug Application; clomifene was third drug for which an IND had been filed under the 1962 Kefauver Harris Amendment to the Federal Food, Drug, and Cosmetic Act that had been passed in response to the thalidomide tragedy. It was approved for marketing in 1967 under the brand name Clomid. It was first used to treat cases of oligomenorrhea but was expanded to include treatment of anovulation when women undergoing treatment had higher than expected rates of pregnancy.
The drug is widely considered to have been a revolution in the treatment of female infertility, the beginning of the modern era of assisted reproductive technology, and the beginning of what in the words of Eli Y. Adashi, was "the onset of the US multiple births epidemic".
The company was acquired by Dow Chemical in 1980, and in 1989 Dow Chemical acquired 67 percent interest of Marion Laboratories, which was renamed Marion Merrell Dow. In 1995 Hoechst AG acquired the pharmaceutical business of Marion Merrell Dow. Hoechst in turn became part of Aventis in 1999, and subsequently a part of Sanofi. It became the most widely prescribed drug for ovulation induction to reverse anovulation or oligoovulation.

Society and culture

Brand names

Clomifene is marketed under many brand names worldwide, including Beclom, Bemot, Biogen, Blesifen, Chloramiphene, Clofert, Clomene, ClomHEXAL, Clomi, Clomid, Clomidac, Clomifen, Clomifencitrat, Clomifene, Clomifène, Clomifene citrate, Clomifeni citras, Clomifeno, Clomifert, Clomihexal, Clomiphen, Clomiphene, Clomiphene Citrate, Cloninn, Clostil, Clostilbegyt, Clovertil, Clovul, Dipthen, Dufine, Duinum, Fensipros, Fertab, Fertec, Fertex, Ferticlo, Fertil, Fertilan, Fertilphen, Fertin, Fertomid, Ferton, Fertotab, Fertyl, Fetrop, Folistim, Genoclom, Genozym, Hete, I-Clom, Ikaclomin, Klofit, Klomen, Klomifen, Lomifen, MER 41, Milophene, Ofertil, Omifin, Ova-mit, Ovamit, Ovinum, Ovipreg, Ovofar, Ovuclon, Ovulet, Pergotime, Pinfetil, Profertil, Prolifen, Provula, Reomen, Serofene, Serophene, Serpafar, Serpafar, Surole, Tocofeno, and Zimaquin.

Regulation

Clomifene is included on the World Anti-Doping Agency list of illegal doping agents in sport. It is listed because it is an "anti-estrogenic substance".

Research

Clomifene has been used almost exclusively for ovulation induction in premenopausal women, and has been studied very limitedly in postmenopausal women.
Clomifene was studied for treatment and prevention of breast cancer, but issues with toxicity led to abandonment of this indication, as did the discovery of tamoxifen. Like the structurally related drug triparanol, clomifene is known to inhibit the enzyme 24-dehydrocholesterol reductase and increase circulating desmosterol levels, making it unfavorable for extended use in breast cancer due to risk of side effects like irreversible cataracts.