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. Zoladex is also used in combination with flutamide for locally confined carcinoma of the prostate. Zoladex is administered as a subcutaneous injection every 28 days. Individuals taking Zoladex 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 Zoladex should also be monitored for high blood sugar and the development of diabetes, as well as for cardiovascular complications.
Zoladex’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. Zoladex 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 with Zoladex.
What are the possible side effects of Zoladex?
Multiple clinical trials evaluated the safety and efficacy of Zoladex. The most common side effects of Zoladex in men are hot flashes, sexual dysfunction, lower urinary tract symptoms, and decreased erections. Injection site reactions are also possible while receiving Zoladex. This is not an exhaustive list of all potential side effects of Zoladex. Talk to your healthcare provider or pharmacist for further information.
Things to note about Zoladex
Several rare but more serious side effects can accompany Zoladex including increased blood sugar, increased calcium levels, hypersensitivity, and injection site injury. Additionally, Zoladex 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 Zoladex should be monitored for any cardiovascular concerns. Zoladex may also cause a decrease in bone mineral density, leading to osteoporosis (thinning of the bones).
Tumor Flare Phenomenon is possible while taking Zoladex, 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 Zoladex. 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 Zoladex, including flutamide.
Before starting Zoladex 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, especially steroids or anticonvulsants, vitamins, or herbal supplements
Zoladex 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, common dosages include 3.6 mg of Zoladex every 28 days or 10.8 mg every 12 weeks.1
Written by: Casey Hribar | Last reviewed: January 2019
Zoladex Prescribing Information. FDA.gov. Feb 2015. Available from: https://www.accessdata.fda.gov/drugsatfda_docs/label/2015/019726s059,020578s037lbl.pdf