Tamoxifen (Zitazonium) Review Article
Tamoxifen, discovered by ICI Pharmaceuticals and sold under the trade names Nolvadex, Zitazonium, is an anti-oestrogen drug which is widely use to treat breast cancer that has spread to other parts of the body in men and women, to treat early breast cancer in women who have already been treated with surgery, radiation or chemotherapy. Is is also known to reduce the risk of developing a more serious type of breast cancer in women who had ductal carcinoma and who have been treated with surgery and radiation and also reduces the risk of breast cancer in women who are at high risk for the disease due their age, personal medical history or family medical history. Tamoxifen is sold as tablets, which come in different strengths: 10mg, 20mg or 30mg and can be taken with or without food. Most common side effects are hot flushes and sweats, nausea and indigestion, change in periods, weight gain or leg cramps, depression or voice changes. Tamoxifen can interact with other medicines so let your doctor know about any drugs you are taking, including non-prescribed drugs. Other Names of Tamoxifen: Nolvadex, Dignatomoxi, Emblon, Fentamox, Istubol, Kessar, Mamofen, Noltam, Novofen, Oestrifen, Tamaxin, Tamifen, Tamoplex, Tamoxen, Valodex, Zitazonium.
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The etiology of breast cancer is unknown, but risk factors have been identified to be associated with it, which includes family history, genetics, gynecological history, oral contraceptive pills, radiation and to a lesser content, diet.
Because of the hazard it poses, several organizations and health activists have advocated the fight against breast cancer. According to the World Health Organization, breast cancer is a type of cancer that is preventable and treatable. With the appropriate awareness, education, and therapy, breast cancer mortalities can be prevented.
Selective Estrogen Receptor Modulator
Tamoxifen is the most widely studied estrogen treatment for breast cancer. It was first synthesized in 1966, and after three decades, it was proven that the success in the fight against breast cancer have been due to its widespread use. In fact, according to Hermon and Beral (1996), the reduction in breast cancer mortality is due Tamoxifen.
ER+ breast cancer is a type of cancer wherein the tumor cells are dependent on estrogen for proliferation - requiring it for their growth. Therefore, selectively antagonizing estrogen on these tumor cells will lead to their diminished activity, leading to decreased proliferation and growth.
Tamoxifen is the first compound of the SERMs drug class. Being a SERM, it acts selectively as an antagonist on estrogen receptors in the breast tissue, but acts as an agonist in other tissues like the uterine endometrium, the coagulation system, bone homeostatis and liver function. The decreased estrogen levels in the breast leads to breast tumor cell inhibition, an effective targeted approach for treating this type of cancer. The agonist effects of Tamoxifen on other systems are responsible for its side effects, as well as other possible indications: endometrial hypertrophy, vaginal bleeding, uterine and endometrial cancers, thromboembolism, bone density modulation and altered blood lipid profile (Ellis and Swain, 2001).
Several studies have proven the effectiveness of Tamoxifen for the treatment of breast cancer. The Tamoxifen Adjuvant Tiral Organization (NATO) study has concluded that there is an overall disease-free survival advantage for patients using Tamoxifen. Two studies made by the Swedish Breast Cancer Cooperative Group in 1996 and Early Breast Cancer Trialists’ Collaborative Group in 1998 have found that a five adjuvant therapy of Tamoxifen is the superior duration of therapy as compared to one or two year use.
Tamoxifen has also been proven to be effective as a prophylactic agent. In the study made by the National Cancer Institute in 1998 and 2005, they have found that Tamoxifen can prevent the development of breast cancer. This finding was similar to the results obtained by Strasser-Weippl and Goss (2004). The National Cancer Institute recommends a five year prophylactic therapy with Tamoxifen; beyond five years, no further benefit has been observed. A 69% reduction in the occurence of ER+ breast cancer was observed in the said study.
In a study made by Williamson and Ellis (2005), they have found that Tamoxifen is an effective agent for inducing ovulation. In their study, 81% patients with anovulatory infertility had a successful ovulation. In the meta-analysis made by Steiner, Terplan and Paulson (2005), they found that the efficacy of Tamoxifen to for inducing ovulation is similar to clomiphene, the first line ovulating agent (Wolf, 2000).
Other Indications: Osteoporosis, Brain Tumors, Gynecomastia
It is known that when a woman reaches the menopausal age, hormonal levels are decreased significantly, specifically estrogen. This decrease in estrogen levels is the reason for the several observed physiological changes in the body, the most significant of which is the effects on the skeletal system. Estrogen promotes bone formation and decreased bone resorption. Due to the decreased estrogen level, menopausal women experiences bone deterioration, and are at a significant risk for having osteoporosis (Prince et al., 1991; Belchetz, 1994).
Tamoxifen, being a SERM, have agonist effects at the bone tissues. It is used as a drug therapy for osteoporosis. Studies made by Love and colleagues (1992), Ramaswamy and Shapiro (2003) have found that Tamoxifen in osteoporosis is therapeutically beneficial. Love and colleagues found that a 0.61% increase in lumbar bone density is possible, while Ramaswamy and Shapiro found that Tamoxifen is able to preserve the mineral density of bones in post menopausal women.
In a study made by Fine and colleagues (2006), they explored the possibility of using Tamoxifen as a treatment for brain tumors. Tamoxifen was found to inhibit P-glycoprotein, an important agent in the development of brain tumors. Fine and colleagues determined the possibility of using Tamoxifen as an adjuvant to paclitaxel for the treatment of metastatic brain tumors – they found that Tamoxifen may be used for brain tumors. Further research is needed to determine if it can be used clinically.
Gynecomastia is a hormonal disorder wherein men develops breast tissue enlargement. It is commonly caused as a consequence of some drugs, but in some instances it is estrogen mediated. Tamoxifen may be used for estrogen mediated gynecomastia, antagonizing estrogen in breast tissues.
Hot flushes is the most common side effect of Tamoxifen (Sweetman, 2009). Hot flushes, nausea and vomiting is experienced by 25% of patients. Other side effects include fluid retention, gastrointestinal intolerance, rashes, dry skin, vaginal bleeding/discharge, dizziness, headache, fatigue and muscle cramps (Sweetman, 2009).
There is a potentially life threatening drug interaction between coumarin anticoagulants like warfarin and Tamoxifen (Ritchie, 1989; Tenni, et al., 1989), where the anticoagulant effects are increased. Prothrombin time prolongation, as well as hematuria and hematoma have all been reported with concomitant use of the two drugs.
In a study made by Kivisto, et al. (1998), it was found that the plasma levels of Tamoxifen are reduced when used together with rifampicin, an antibacterial used for tuberculosis. It was hypothesized that this was due to the enzyme inducing effects of the said antibacterial.
The effects of bromocriptine, a dopaminergic agent used in Parkinson’s disease, are increased when concomitantly used with Tamoxifen.
Precautions and Safety
It is recommended that the patients who are at risk for thromboembolism to avoid using Tamoxifen, due to the reports of thromboembolitic and pulmonary embolitic events. In a cohort study by McDonald and colleagues (1995), they have proven that Tamoxifen predisposes patients to a higher risk for thromboembolism. Though anticoagulants may be used, drug interaction is also of concern.
As mentioned, Tamoxifen is a SERM with agonistic effects in the uterus. Tamoxifen stimulates the endometrieum, which may predispose patients to the development of uterine (Wickerham, 2002) and endometrial cancer (Fisher, et.al., 1998, 2005), as well as endometrial polyps (Buijs, et al., 2004). The increased risk of developing cancer was found to be 2.53x more than those not using Tamoxifen (Fisher, et al., 1998). According to the American College of Obstetrics and Gynecologists, it is recommended that should the first signs of hyperplasia develops, Tamoxifen is stopped and hysterectomy is considered.
As a treatment for breast cancer, the recommended dose of Tamoxifen is 20mg daily, given once or in two divided doses. Studies suggest that adjuvant therapy be continued up to five years (Sweetman, 2009).
As a prophylactic agent for high risk patients, the approved dose of Tamoxifen is 20mg daily given for five years (Sweetman, 2009).
Lastly, for induction of ovulation, 20mg Tamoxifen on day 2 to day 5 of the menstrual cycle is recommended. For patients with irregular menstrual cycle, Tamoxifen is given on any day. If menstruation occurs, dosing is then given every day 2 of the cycle. If there is no response, a subsequent dose is given 45 days after the initial treatment (Sweetman, 2009).
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Tamoxifen (Zitazonium) Review Article