|Systematic (IUPAC) name|
|Metabolism||Hepatic (with enterohepatic circulation)|
|Excretion||Mainly renal, some biliary|
|Mol. mass||406 or 598.10 (with citrate)|
|(what is this?)|
Clomifene (INN) or clomiphene (USAN) (trademarked as Androxal, Clomid and Omifin) is a selective estrogen receptor modulator (SERM) that has become the most widely prescribed drug for ovulation induction to reverse anovulation or oligoovulation.
Use in anovulation
Clomifene is useful 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.
Clomid can be initiated at a dose of 50 mg daily for 5 days, starting on cycle day 3, 4, or 5 (where cycle day 1 is the first day of the menstrual period), thus being taken on cycle days 3-7, 4-8 or 5-9. During a clomifene-induced cycle, there should be frequent intercourse (every other day) the week before and including the estimated day of ovulation, (cycle days 9-18). If LH surge detection tests are used, these tests should be started 3 to 4 days after the last clomifene tablet is taken (that is, if taking clomifene on cycle days 4-8, LH surge tests should be started on cycle day 11) and continue until ovulation is indicated (that is, the test becomes positive.) or through cycle day 18. If there is no spontaneous surge, there may be an artificial triggering of oocyte release if there is an ovarian follicle of over 20 mm in size, such as by an intramuscular injection of 10,000 units of hCG. However, routinely using oocyte release triggering with hCG appears to decrease pregnancy chances compared to frequent monitoring with LH tests.
The following procedures may be used to monitor induced cycles:
- Follicular monitoring with vaginal ultrasound, starting 4-6 days after last pill. Serial transvaginal ultrasound can reveal the size and number of developing follicles. It can also provide presumptive evidence of ovulation such as sudden collapse of the preovulatory follicle, and an increase in fluid volume in the rectouterine pouch. After ovulation, it may reveal signs of luteinization such as loss of clearly defined follicular margins and appearance of internal echoes.
- Serum estradiol levels, starting 4-6 days after last pill
- Post-coital test 1-3 days before ovulation to check whether there are at least 5 progressive sperm per HPF
- Adequacy of LH surge by urine LH surge tests 3 to 4 days after last clomifene pill
- Mid-luteal progesterone, with at least 10 ng/ml 7-9 days after ovulation being regarded as adequate.
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.
The most common adverse drug reaction associated with the use of clomifene (>10% of people) is reversible ovarian enlargement. Less common effects (1-10% of people) include visual symptoms (blurred vision, double vision, floaters, eye sensitivity to light, scotomata), headaches, vasomotor flushes (or hot flashes), abnormal uterine bleeding and/or abdominal discomfort. Rare adverse events (<1% of people) include: high blood level of triglycerides, liver inflammation, reversible baldness and/or ovarian hyperstimulation syndrome.
Some studies have suggested that clomifene citrate 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 corroborate those findings. This however is disputed and some feel there is no significant increase in risk.
The incidence of fetal and neonatal abnormalities for patients on clomifene for fertility is similar to that seen in the general population. There is no data to suggest a higher rate of congenital anomalies or spontaneous abortions after using this drug.
Mechanism of action
Clomifene inhibits estrogen receptors in the hypothalamus, inhibiting negative feedback of estrogen on gonadotropin release, leading to up-regulation of the hypothalamic–pituitary–gonadal axis. Zuclomifene, a more active isomer, stays bound for longer periods of time. Clomifene is not a steroid drug.
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 beta-hCG. 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 level is rising steadily, causing 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 (FSH, LH) release. (It should be noted that more rapid, lower amplitude pulses of GnRH lead to increased LH/FSH secretion, while more irregular, larger amplitude pulses of GnRH leads to a decrease in the ratio of LH/FSH.) Increased FSH level causes growth of more ovarian follicles, and subsequently rupture of follicles resulting in ovulation. Ovulation occurs most often 6–7 days after a course of clomifene.
Clomifene is a mixture of two geometric isomers, enclomifene (E-clomifene) and zuclomifene (Z-clomifene). These two isomers have been found to contribute to the mixed estrogenic and anti-estrogenic properties of clomifene.
Off-label use in the treatment of male hypogonadism
Clomifene citrate has been found very effective in the treatment of secondary male hypogonadism in many cases. This has shown to be a much more attractive option than testosterone replacement therapy (TRT) in many cases because of the reduced cost and convenience of taking a pill as opposed to testosterone injections or gels. Unlike traditional TRT it also does not shrink the testes and as a result can enhance fertility. Traditional TRT has the risk of inducing a chemical gonadectomy, although with monitoring and low-dose hCG as adjunct, this is usually preventable and reversible. Because clomifene citrate has not been FDA approved for use in males it is prescribed off-label. Due to the fact that Clomifene is now a generic medication in most markets, it is unlikely that a drug company would pursue FDA approval for use in men now because of limited profit incentive, mostly due to the relatively small market potential. However, the single isomer of clomifene, enclomiphene under the brand name Androxal, is currently under phase 3 trials for use in men.
Clomifene is used by males (especially steroid users at the end of a cycle) to reduce the physical effects caused by high oestrogen levels, such as gynecomastia. The drug binds to oestrogen receptors to prevent the hormone from binding and therefore taking effect. It also restores the body's natural production of testosterone. It is included on the World Anti-Doping Agency list of illegal doping agents in sport.
Clomifene has been used since the 1960s. 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.
In April 1989, a patent was awarded to Yale University Medical researchers Dr. Florence Comite and Dr. Pamela Jensen for the use of clomiphene to predict fertility in women. A woman capable of sustaining pregnancy would develop denser bone mass while on clomiphene; the bone mass increase would be predictive of fertility, and the changes could be detected on a CT scanner.
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