Tamoxifen

Benjamin Clanner-Engelshofen is a freelance writer in the medical department. He studied biochemistry and pharmacy in Munich and Cambridge / Boston (USA) and noticed early on that he particularly enjoyed the interface between medicine and science. That is why he went on to study human medicine.

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The active ingredient tamoxifen is used in the treatment of breast cancer. It works specifically at the docking points (receptors) of female sex hormones (estrogen and progesterone) and can thus inhibit the growth of hormone-dependent tumors. Compared to other active ingredients for cancer treatment, tamoxifen has a clear potential for side effects. It has therefore been used frequently for the treatment of breast cancer, especially since patent protection expired in 2002. Here you can read everything you need to know about the effects of tamoxifen, side effects and use.

This is how tamoxifen works

The body's own female hormone estrogen (also: estrogen) not only determines the woman's cycle, but also has other tasks in the body. Among other things, it ensures strong bones (a lack of estrogen can lead to osteoporosis) and stimulates the immune system. When estrogens are released in the body, they reach the target tissue via the bloodstream. Once there, they specifically influence the target cell and can, among other things, stimulate cell growth. If a cell has many docking points (receptors) for estrogens, it is particularly sensitive to the hormone.

In a large number of breast tumors there is an increased number of estrogen receptors. The cells, which are already degenerate, are stimulated by the natural estrogen to grow and divide, i.e. to multiply, which causes the tumor to grow in an uncontrolled manner.

Tamoxifen and especially its metabolite hydroxytamoxifen can bind to the estrogen receptors without stimulating cell division and reproduction. This blocks the existing receptors and can no longer be activated by the natural estrogen.

Uptake, breakdown and excretion of tamoxifen

After taking tamoxifen tablets, the active ingredient is well absorbed in the intestine and reaches its maximum blood level after four to seven hours. The metabolism, which takes place mainly in the liver, leads to much more effective breakdown products. These are then mainly excreted with the stool, but this takes some time: the active ingredient is only half broken down and excreted after about a week.

When is tamoxifen used?

The active ingredient tamoxifen is approved for the treatment of hormone-dependent breast tumors: It can be used as a support after primary treatment for breast cancer or for breast cancer that has already formed daughter tumors (metastases). The application usually takes place over a longer period of time.

This is how tamoxifen is used

The active ingredient is administered in the form of tablets. The usual tamoxifen dosage is twenty milligrams per day, but it can be increased up to forty milligrams if necessary. It is taken with a meal to reduce undesirable effects such as nausea.

What are the side effects of tamoxifen?

Tamoxifen side effects in more than one in ten women treated are nausea, rash, fluid retention in the tissues, vaginal discharge and bleeding, cycle changes and menopausal symptoms such as hot flashes and exhaustion.

Every hundredth to tenth patient experiences drowsiness, headache, visual disturbances, vomiting, diarrhea, constipation, hair loss, hypersensitivity reactions, muscle pain, leg cramps, blood clots, temporary anemia and itching of the genitals. Another tamoxifen side effect may be a change in laboratory values ​​(increased blood lipid values, changes in liver enzyme values).

What should be considered when taking tamoxifen?

Tamoxifen therapy aims to reduce the effect of the body's own estrogen. An additional supply of estrogen in the form of hormonal contraceptives (for example "the pill") would not make sense and should therefore be avoided.

Tamoxifen affects blood clotting by reducing the number of platelets in the blood. If anticoagulant medication is also given, the anticoagulant effect can be increased. Examples of such “anticoagulants” are acetylsalicylic acid and other platelet aggregation inhibitors, as well as coumarin-like anticoagulants such as warfarin and phenprocoumon.

Tamoxifen is converted into the more active form of action by certain liver enzymes. Medicinal substances that inhibit these enzymes or promote their activity can thereby influence the metabolism and thus the effectiveness of the cancer drug. For example, antidepressants from the group of selective serotonin reuptake inhibitors (SSRIs, such as paroxetine and fluoxetine) and the antidepressant bupropion can reduce the effectiveness of tamoxifen by inhibiting enzymes. The simultaneous use of such drugs should therefore be avoided as far as possible.

Since there is little data on the use of tamoxifen during pregnancy and breastfeeding, the active ingredient must not be taken during this time. In animal studies, the use of tamoxifen caused harm to the unborn child.

Also, due to a lack of knowledge, its use in children and adolescents is not indicated (contraindicated).

How to get medication with tamoxifen

Preparations containing tamoxifen can be obtained from pharmacies with a prescription.

Since when has tamoxifen been known?

As early as the late 1950s, pharmaceutical companies were actively researching anti-estrogens (i.e. active ingredients that inhibit the effects of estrogen) for effective contraception. In doing so, Dr. Dora Richardson, an employee of an English pharmaceutical company, discovered the active ingredient tamoxifen in 1966. However, this was not suitable for contraception, which is why it was first forgotten. It was later discovered that estrogens can also accelerate the growth of breast cancer. As a result, a clinical study on tamoxifen was started in 1971 at Christie Hospital in Manchester, one of the largest cancer clinics in Europe. Based on the positive study results, tamoxifen was marketed for late-stage breast cancer treatment in 1973.

More interesting facts about tamoxifen

Tamoxifen is misused by male athletes as a doping agent: it increases testosterone levels, which stimulates muscle growth. Tamoxifen also prevents a common side effect of anabolic steroids, the so-called "man's breasts" (gynecomastia).

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