What Is Goserelin (Zoladex<sup>®</sup>)?
Zoladex® (goserelin) is a Gonadotropin Releasing Hormone (GnRH) agonist (also called LHRH agonists). It is indicated for use as a palliative treatment option for individuals with advanced carcinoma of the prostate. Goserelin is also used in combination with flutamide for locally confined carcinoma of the prostate. Zoladex is administered as a subcutaneous injection every 28 days, or every 12 weeks, depending on the patient’s dosage schedule. Individuals taking goserelin should be closely monitored, especially during the first several weeks of treatment, as tumor flare can occur. Tumor flare is the worsening of tumor symptoms early on during treatment that can lead to spinal cord compression and other adverse effects. Individuals taking goserelin should also be monitored for high blood sugar and the development of diabetes, as well as for cardiovascular complications.
How does goserelin work?
Goserelin’s active ingredient is a Gonadotropin-Releasing Hormone (GnRH) agonist. This means, that its purpose is to activate the GnRH receptor by mimicking the receptor’s normal activator. Prostate cancer tumors are often fueled to grow by androgens, including testosterone. Turning off the body’s ability to produce testosterone, or reducing the amount made can potentially halt tumor growth. Goserelin continuously activates a key receptor in the pathway to making testosterone, and eventually overwhelms the receptor. When the receptor is overwhelmed, or desensitized, it decreases luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are key in making testosterone. This is also known as medical or chemical castration.
However, a major concern with desensitizing the GnRH receptor is that before the receptor becomes overwhelmed, it will be continuously activated for the first few weeks of treatment. This means that more testosterone will be produced than usual, and could potentially cause a short term surge in tumor growth, known as Tumor Flare Phenomenon. Risk of tumor flare can be decreased by taking an antiandrogen at the start of treatment with goserelin.
What are the possible side effects of goserelin?
Multiple clinical trials evaluated the safety and efficacy of goserelin. The most common side effects of goserelin in men include hot flashes, sexual dysfunction, lower urinary tract symptoms, and decreased erections. Injection site reactions are also possible while receiving goserelin. This is not an exhaustive list of all potential side effects of goserelin. Talk to your healthcare provider or pharmacist for further information.
Things to note about goserelin
Several rare but more serious side effects can accompany goserelin including increased blood sugar, increased calcium levels, hypersensitivity, and injection site injury. Additionally, goserelin may increase an individual’s risk of developing diabetes and cardiovascular complications, including an increased risk of heart attack, stroke, and sudden cardiac death. Individuals taking goserelin should be monitored for any cardiovascular concerns. Goserelin may also cause a decrease in bone mineral density, leading to osteoporosis (thinning of the bones).
Tumor Flare Phenomenon is possible while taking goserelin, in which tumor growth is accelerated for a short time before it is halted. Alert your provider immediately if you notice any serious signs of Tumor Flare Phenomenon including:
- Weakness or loss of feeling in legs
- Have blood in the urine
- Have trouble urinating or are unable to urinate
- Experience new or worsening bone pain
There is also a risk of developing an injection site injury while taking goserelin. Alert your provider immediately if you notice any of the following symptoms related to an injection site injury:
- Abdominal bloating or pain
- Dizziness or lightheadedness
- Shortness of breath
- Signs of confusion
You should also contact your provider if you notice any signs of an allergic reaction to the medication, including chest pain or difficulty breathing. It is also important to consult the prescribing information for any other medications taken with goserelin, including flutamide.
Before starting goserelin talk to your provider if you:
- Have any heart or blood vessel conditions such as irregular heart beat
- Are taking any medications for any cardiovascular conditions
- Have high blood pressure
- Have a condition that affects the strength of your bones
- If you are a heavy drinker or smoker
- Are taking any other medications (prescription and over-the-counter), vitamins, or herbal supplements
Goserelin is administered subcutaneously (an injection under the skin) under the supervision of a healthcare provider. Your doctor will determine the appropriate dosage and administration timeline for you; however, depending on the medication dosage, goserelin is typically administered either every 28 days or every 12 weeks. Patients should talk to their doctor if they have any questions, or if they have questions regarding their goserelin regimen.1
These are not all the possible side effects of goserelin. Patients should talk to their doctor about what to expect with treatment with goserelin.