Buserelin is a synthetic analog of natural gonadotropin-releasing hormone and is used to treat prostate cancer. Buserelin, also called buserelin acetate, is sold under the brand name Suprefact in Canada. It is not commercially available in the U.S. for human use.
Androgens, particularly testosterone, appear to play a major role in prostate cancer. Buserelin inhibits production of luteinizing hormone from the pituitary gland which decreases the levels of testosterone. Prostate cancer is often sensitive to testosterone levels, thus, a reduction in testosterone may influence the rate of cancer growth progression and affect the size of the tumor. Hormone therapy with buserelin cannot cure prostate cancer but may decrease symptoms and improve the quality of life for most patients.
Breast cancer may also treated with buserelin. A research study examined combined treatment with buserelin and tamoxifen in women with premenopausal metastatic breast cancer. Together, these drugs were more effective and resulted in longer overall survival than treatment with either drug alone.
Buserelin indirectly decreases the testosterone levels in the body. Testosterone is produced in the testes and the adrenal glands, but the testes will only produce testosterone if adequate levels of luteinizing hormone are present. Buserelin reduces the production of luteinizing hormone, thus causing a drop in testosterone levels. When buserelin administration is started, a brief increase in the hormone levels in the first few days or weeks may occur.
Two dosage forms of buserelin are available. Either as an injection (1 mg/mL multidose vial) or as an intranasal spray (100 mcg/spray).
A dose of 500 mcg (0.5 milligrams [mg]) is injected under the skin three times per day for seven days every eight hours. The doctor may lower the dose to 200 micrograms (mcg) or 0.2 mg once a day with time if required. Treatment with the nasal spray form of the drug is administered at 200 mcg, (2 sprays) into each nostril every eight hours. The doctor determines the duration of treatment.
Buserelin induces a temporary rise in sex hormones at the start of treatment, but they usually remain within the normal range. This rise may be associated with an increase in disease symptoms in some patients. Symptoms such as bone pain, impaired urination, and muscular weakness in the legs may occur with the temporary increase in tumor activity. These symptoms usually ease gradually, although they can be avoided altogether by prescribing an antiandrogen such as cyproterone acetate or flutamide at the same time.
Due to these effects, it is advisable for patients to also take an antiandrogen with buserelin if a temporary increase in the size of the tumor may lead to: urinal tract obstruction, increased intracranial pressure (in rare cases with brain metastases), or paresis (slight or incomplete paralysis) due to increased pressure on the spinal cord. Antiandrogen treatment should be started about five days before buserelin and for three to four weeks along with buserelin therapy until the sex hormones have returned to an acceptable level.
Buserelin causes sterility in men and menopause in women which may be permanent. It is not known if buserelin is safe to use during pregnancy. Due to the secretion into breast milk, breast-feeding is not recommended. In addition, it is not known if buserelin is mutagenic or carcinogenic.
Alert doctors or dentists about buserelin therapy before receiving any treatment.
Many people have very few side effects with buserelin, while others may experience more.
Skin reaction at the injection site. The injection may be slightly uncomfortable, and redness might occur at the injection site following administration.
Headache (when administered through the nasal passage).
Burning, swelling, and/or itching at place of injection.
Loss of libido and impotence during treatment.
Breast tenderness or fullness. Slight breast swelling and tenderness may occur. This side effect can be reduced with medication.
Feelings of sickness and diarrhea. They are usually mild and controlled easily.
Dry nose (when administered through the nasal passage).
Tumor flare. Because buserelin may temporarily increase testosterone levels for the first few days or weeks of treatment, an increase in symptoms may be experienced. Serious disease flare reactions may occur such as an increase in bone pain, spinal cord compression, or urinary tract obstruction.
Thrombosis with pulmonary embolism.
Calcium loss in the skeleton (women).