FIRMAGON (Degarelix)
GnRH Receptor Antagonist for Prostate Cancer Treatment
Quick Facts About FIRMAGON
Key Takeaways About FIRMAGON
- No testosterone flare: Unlike GnRH agonists, FIRMAGON achieves castration-level testosterone without an initial surge, reducing the risk of disease flare
- Rapid onset: Testosterone levels drop to castration levels within 3 days of the first injection, providing fast disease control
- Monthly injections: After the initial loading dose (2 × 120 mg), maintenance is a single 80 mg subcutaneous injection every 28 days
- Injection site reactions are common: Pain, redness, and swelling at the injection site are the most frequently reported side effects, especially with the first dose
- Cardiovascular monitoring important: Patients with heart conditions should be closely monitored as FIRMAGON may affect heart rhythm (QT prolongation)
What Is FIRMAGON and What Is It Used For?
FIRMAGON (degarelix) is a synthetic hormone blocker classified as a GnRH receptor antagonist. It is used to treat advanced hormone-dependent prostate cancer and high-risk localized prostate cancer before and during radiotherapy. It works by directly blocking GnRH receptors in the pituitary gland, thereby rapidly lowering testosterone levels that fuel prostate cancer growth.
Prostate cancer is one of the most commonly diagnosed cancers in men worldwide. Many prostate cancers are hormone-dependent, meaning they rely on the male hormone testosterone for growth and progression. Androgen deprivation therapy (ADT) — reducing testosterone to very low levels — remains a cornerstone treatment for advanced prostate cancer. FIRMAGON achieves this therapeutic goal through a distinct mechanism that sets it apart from older hormonal treatments.
Degarelix, the active ingredient in FIRMAGON, mimics the natural gonadotropin-releasing hormone (GnRH) but acts as a competitive antagonist. When injected, it binds directly to GnRH receptors on the anterior pituitary gland, preventing the natural GnRH hormone from activating these receptors. This blockade immediately reduces the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in turn causes a rapid decline in testosterone production by the testes.
The clinical significance of this mechanism cannot be overstated. Traditional GnRH agonists (such as leuprolide or goserelin) initially stimulate the pituitary gland before eventually desensitizing it, causing a temporary surge in testosterone known as a “flare.” This flare can worsen symptoms in patients with advanced disease, potentially causing bone pain, urinary obstruction, or even spinal cord compression. FIRMAGON bypasses this problem entirely — testosterone levels begin to fall immediately after the first injection and typically reach castration levels (below 0.5 ng/mL) within just 3 days.
FIRMAGON is approved for two primary indications: the treatment of advanced hormone-dependent prostate cancer in adult men, and the treatment of high-risk localized or locally advanced prostate cancer before and in combination with radiotherapy. In both settings, the goal is to suppress testosterone to levels that inhibit cancer cell growth and proliferation.
FIRMAGON directly blocks GnRH receptors in the pituitary gland, immediately reducing the release of LH and FSH. This leads to a rapid and sustained drop in testosterone levels without the initial testosterone surge seen with GnRH agonists. Castration-level testosterone is typically achieved within 3 days of the first injection.
What Should You Know Before Taking FIRMAGON?
Before starting FIRMAGON, inform your doctor about any heart conditions, diabetes, liver disease, kidney problems, or history of severe allergic reactions. FIRMAGON is not suitable for women, children, or people allergic to degarelix. Certain medications, particularly those affecting heart rhythm, may interact with FIRMAGON.
Contraindications
FIRMAGON must not be used if you are allergic (hypersensitive) to degarelix or any of the other ingredients in the medicine. The inactive ingredients include mannitol (E421) and water for injections. If you have ever experienced a severe allergic reaction to any GnRH analogue, inform your healthcare provider before treatment, as cross-reactivity may occur in rare cases.
FIRMAGON is indicated exclusively for adult men and must not be used in women or children. There is no therapeutic indication for FIRMAGON in the pediatric population, and its effects on developing bodies have not been studied.
Warnings and Precautions
Several medical conditions require special attention and monitoring during FIRMAGON treatment. Before starting therapy, discuss the following with your doctor:
- Cardiovascular conditions or heart rhythm disorders (arrhythmias): FIRMAGON may prolong the QT interval on an electrocardiogram (ECG), which can increase the risk of abnormal heart rhythms. This risk is particularly relevant if you are already taking medications that affect heart rhythm. Your doctor may recommend ECG monitoring before and during treatment.
- Diabetes mellitus: Androgen deprivation therapy with FIRMAGON can worsen pre-existing diabetes or trigger new-onset diabetes. If you have diabetes, you may need more frequent blood glucose monitoring. Insulin or oral diabetes medication doses may require adjustment.
- Liver disease: Liver function may need to be monitored during treatment, as elevated liver enzymes have been reported in some patients. Inform your doctor if you have any pre-existing liver conditions.
- Kidney disease: FIRMAGON has not been specifically studied in patients with severe renal impairment. If you have significant kidney problems, your doctor will weigh the benefits against the potential risks.
- Osteoporosis or bone health concerns: Long-term testosterone suppression reduces bone mineral density, increasing the risk of osteoporosis and fractures. Your doctor may recommend bone density monitoring, calcium and vitamin D supplementation, and weight-bearing exercise to mitigate this risk.
- History of severe hypersensitivity reactions: FIRMAGON has not been studied in patients with a history of severe allergic reactions. If you have such a history, treatment should be initiated with caution and appropriate monitoring.
Androgen deprivation therapy, including treatment with FIRMAGON, may increase the risk of cardiovascular events including heart attack and stroke. Patients with pre-existing cardiovascular disease should be carefully evaluated before starting treatment. Regular cardiovascular monitoring is recommended throughout therapy.
Use in Women
FIRMAGON is indicated exclusively for the treatment of prostate cancer in adult men. It is not intended for use in women. Women who are pregnant or may become pregnant should not handle FIRMAGON, as the active substance could potentially be absorbed through the skin. If accidental skin contact occurs, the affected area should be washed immediately with soap and water.
How Does FIRMAGON Interact with Other Drugs?
FIRMAGON may interact with medications that affect heart rhythm (QT-prolonging drugs), including certain antiarrhythmics, antibiotics, antipsychotics, and pain medications. Always provide your doctor with a complete list of all medications you are taking, including prescription drugs, over-the-counter medicines, and herbal supplements.
The most clinically significant drug interactions with FIRMAGON involve medications that can prolong the QT interval on an electrocardiogram. When these drugs are taken together with FIRMAGON, the combined effect on heart rhythm may be greater than either drug alone, potentially leading to dangerous arrhythmias.
Major Interactions
The following medications have known interactions with FIRMAGON that may require medical intervention, dose adjustment, or careful monitoring:
| Drug | Class | Interaction Type | Clinical Concern |
|---|---|---|---|
| Quinidine | Antiarrhythmic (Class IA) | QT prolongation | Increased risk of torsades de pointes |
| Procainamide | Antiarrhythmic (Class IA) | QT prolongation | Increased risk of torsades de pointes |
| Amiodarone | Antiarrhythmic (Class III) | QT prolongation | Additive QT prolongation; monitor ECG |
| Sotalol | Antiarrhythmic (Class III) | QT prolongation | Additive QT prolongation; monitor ECG |
| Methadone | Opioid analgesic | QT prolongation | Risk of cardiac arrhythmias |
| Moxifloxacin | Fluoroquinolone antibiotic | QT prolongation | Additive QT prolongation risk |
| Cisapride | Gastrointestinal prokinetic | QT prolongation | Avoid concomitant use |
Other Considerations
Antipsychotic medications, including haloperidol, chlorpromazine, and certain atypical antipsychotics, are also known to prolong the QT interval. If you are taking any antipsychotic medication, your doctor should be aware of this before initiating FIRMAGON therapy.
While FIRMAGON is not extensively metabolized by the cytochrome P450 enzyme system, it is advisable to inform your doctor about all medications you are currently taking, including over-the-counter medicines, vitamins, and herbal supplements. This is particularly important because the cardiovascular effects of androgen deprivation therapy may be compounded by other medications or conditions.
Fatigue and dizziness are common side effects of FIRMAGON that may impair your ability to drive a car or operate machinery. These effects can be caused by the treatment itself or may be symptoms of the underlying disease. Do not drive or operate heavy machinery until you know how FIRMAGON affects you.
What Is the Correct Dosage of FIRMAGON?
FIRMAGON is given as a subcutaneous injection by a healthcare professional. The starting dose is two 120 mg injections on the first day, followed by one 80 mg injection every 28 days as maintenance. The injection is given in the abdominal area and the site should be varied between injections.
FIRMAGON must always be administered by a healthcare professional (doctor or nurse) as a subcutaneous injection. The medication is supplied as a powder that must be reconstituted (mixed with the provided solvent) immediately before injection. Self-administration is not recommended due to the need for proper reconstitution technique and deep subcutaneous injection.
Adults
Starting Dose (Day 1)
240 mg total: Two subcutaneous injections of 120 mg each, administered consecutively in the abdominal region. The two injections should be given at different sites on the abdomen.
Maintenance Dose (From Month 2 Onwards)
80 mg: One subcutaneous injection of 80 mg given once every 28 days. The injection site should be varied within the abdominal area to minimize injection site reactions.
| Phase | Dose | Number of Injections | Frequency |
|---|---|---|---|
| Loading dose (Day 1) | 2 × 120 mg (240 mg total) | 2 injections | Once (first day only) |
| Maintenance dose | 80 mg | 1 injection | Every 28 days |
Children and Adolescents
FIRMAGON is not indicated for use in children or adolescents. There are no approved pediatric dosing recommendations for degarelix. This medication should only be used in adult men for the treatment of prostate cancer.
Elderly Patients
No dose adjustment is required for elderly patients. However, since prostate cancer predominantly affects older men, most clinical trial participants were over 65 years of age. Elderly patients may be more susceptible to certain side effects, particularly cardiovascular events, bone loss, and metabolic changes. Regular monitoring is recommended.
Missed Dose
If you miss your scheduled monthly injection, contact your doctor or clinic as soon as possible. It is important to maintain consistent testosterone suppression throughout treatment. Missing a dose can allow testosterone levels to rise, which may permit disease progression. Your healthcare team will advise you on the best course of action to get back on schedule.
Overdose
Since FIRMAGON is administered by healthcare professionals in a clinical setting, the risk of overdose is minimal. In clinical studies, no specific overdose events have been reported. If an overdose were to occur, treatment would be supportive and symptomatic, as there is no specific antidote for degarelix.
FIRMAGON must ONLY be injected subcutaneously (under the skin). It must NOT be injected into a blood vessel (intravenously). Before injecting, the healthcare professional should pull back the plunger to check for blood. If blood appears in the syringe, the product must not be used and should be discarded. Injection sites should not be in areas subject to pressure such as around the waistband, belt line, or near the ribs.
What Are the Side Effects of FIRMAGON?
Like all medicines, FIRMAGON can cause side effects, although not everybody gets them. The most common side effects are hot flashes and injection site reactions (pain, redness, swelling). Serious but rare side effects include severe allergic reactions, heart attack, and heart failure. Contact your doctor immediately if you experience severe symptoms.
Side effects of FIRMAGON are largely consistent with those expected from androgen deprivation therapy in general, plus injection-site reactions specific to the subcutaneous route of administration. It is important to understand that many of these side effects result from the intended therapeutic effect — lowering testosterone levels — rather than direct drug toxicity. Below is a comprehensive overview organized by frequency.
Very Common
Affects more than 1 in 10 patients
- Hot flashes (vasomotor symptoms)
- Injection site reactions: pain, redness, and swelling (more common with the starting dose than maintenance doses)
Common
Affects up to 1 in 10 patients
- Injection site swelling, hardening, and nodule formation
- Chills, fever, or flu-like symptoms after injection
- Insomnia (difficulty sleeping)
- Fatigue and dizziness
- Headache
- Weight gain
- Nausea and diarrhea
- Elevated liver enzymes
- Increased sweating (including night sweats) and skin rash
- Anemia (low red blood cell count)
- Musculoskeletal pain and discomfort
- Decreased testicle size
- Breast swelling (gynecomastia)
- Erectile dysfunction (impotence)
Uncommon
Affects up to 1 in 100 patients
- Loss of sexual desire, testicular pain, pelvic pain, ejaculation failure
- Depression, mental impairment
- Skin redness (flushing), hair loss, skin nodules, numbness
- Allergic reactions, hives (urticaria), itching
- Decreased appetite, constipation, vomiting, dry mouth, abdominal pain
- Elevated blood sugar/diabetes, increased cholesterol, changes in blood calcium, weight loss
- High blood pressure, changes in heart rhythm, QT prolongation on ECG, palpitations
- Shortness of breath, swollen hands and feet (peripheral edema)
- Muscle weakness, muscle spasms, joint swelling/stiffness, osteoporosis, joint tenderness
- Frequent or urgent urination, difficulty urinating, painful urination, nighttime urination, incontinence
- Blurred vision
- Vasovagal reactions at injection site (drop in blood pressure, slow heart rate)
- General malaise
Rare and Very Rare
Affects fewer than 1 in 1,000 patients
- Febrile neutropenia (very low white blood cell count with fever)
- Heart attack (myocardial infarction) and heart failure
- Rhabdomyolysis (serious muscle breakdown that can damage the kidneys) — seek immediate medical attention for unexplained muscle pain, cramps, tenderness, or weakness
- Injection site infection, abscess, or tissue necrosis (very rare)
Contact your doctor or go to the emergency department immediately if you experience severe skin rash, itching and difficulty breathing (signs of a serious allergic reaction), unexplained severe muscle pain or weakness (possible rhabdomyolysis), chest pain or sudden shortness of breath (possible heart attack), or signs of injection site infection (increasing redness, warmth, and pus).
Most injection site reactions are mild to moderate and resolve within a few days. Injection site reactions tend to be more pronounced with the initial loading dose (2 × 120 mg) compared to the monthly maintenance dose (80 mg). Your healthcare provider will rotate the injection site within the abdominal area to minimize local reactions.
Long-term side effects of androgen deprivation therapy, including FIRMAGON, may include metabolic changes (weight gain, insulin resistance, unfavorable lipid profile changes), bone loss (osteoporosis), cardiovascular risks, and psychological effects (mood changes, cognitive changes). Your healthcare team should monitor for these effects throughout the duration of treatment and may recommend lifestyle modifications, calcium and vitamin D supplementation, and regular bone density assessments.
How Should You Store FIRMAGON?
Store FIRMAGON at room temperature with no special storage requirements. The powder and solvent should be kept out of the reach of children. After reconstitution, the solution should be used immediately or within 2 hours at 25°C (77°F). Do not use the medicine after the expiry date printed on the packaging.
FIRMAGON is supplied as a powder for reconstitution in vials, together with pre-filled syringes containing the solvent. The unopened vials and syringes have no special storage temperature requirements and can be kept at room temperature.
Once the powder has been reconstituted (dissolved in the solvent), the resulting solution has a limited shelf life. Chemical and physical stability has been demonstrated for 2 hours at 25°C. However, due to the risk of microbiological contamination, the reconstituted solution should ideally be used immediately after preparation. If it is not used immediately, the user bears responsibility for ensuring appropriate storage conditions and timing.
Always check the expiry date on the outer carton, vial, and syringe before use. The expiry date refers to the last day of the stated month. Do not use FIRMAGON if the packaging is damaged or shows signs of tampering.
Unused medicine or pharmaceutical waste should be disposed of in accordance with local requirements. Do not flush medicines down the drain or throw them in household waste. Ask your pharmacist about proper disposal methods to help protect the environment.
What Does FIRMAGON Contain?
Each FIRMAGON vial contains 80 mg of degarelix (as acetate) as the active ingredient, with mannitol (E421) as an excipient. The solvent is water for injections. When reconstituted, each milliliter of solution contains 20 mg of degarelix.
FIRMAGON is presented as a white to off-white powder that must be reconstituted with the clear, colorless solvent (sterile water for injections) provided in a pre-filled syringe. The reconstituted solution should be clear and free of visible particles before injection.
Active Ingredient
Degarelix (as acetate) — 80 mg per vial. Degarelix is a synthetic decapeptide (a chain of 10 amino acids) that acts as a potent GnRH receptor antagonist. When dissolved in 4.2 mL of solvent, the resulting solution contains 20 mg/mL of degarelix.
Inactive Ingredients
- Mannitol (E421) — a sugar alcohol used as a bulking agent in the powder formulation to facilitate reconstitution and ensure proper lyophilization (freeze-drying)
- Water for injections — 4.2 mL provided in the pre-filled syringe as the reconstitution solvent
Pack Sizes
FIRMAGON is available in two pack sizes:
- Single-tray pack: 1 vial containing 80 mg degarelix powder, 1 pre-filled syringe with 4.2 mL solvent, 1 plunger rod, 1 vial adapter, and 1 injection needle
- Triple-tray pack: 3 vials containing 80 mg degarelix powder each, 3 pre-filled syringes with 4.2 mL solvent each, 3 plunger rods, 3 vial adapters, and 3 injection needles
Not all pack sizes may be marketed in your country.
Frequently Asked Questions About FIRMAGON
FIRMAGON (degarelix) is a GnRH receptor antagonist used for the treatment of advanced hormone-dependent prostate cancer in adult men. It is also used for the treatment of high-risk localized or locally advanced prostate cancer before and in combination with radiotherapy. FIRMAGON works by blocking GnRH receptors in the pituitary gland, which rapidly reduces testosterone levels to castration levels without causing an initial testosterone surge.
The key difference is that FIRMAGON is a GnRH receptor antagonist, meaning it directly blocks GnRH receptors. GnRH agonists (like leuprolide or goserelin) initially stimulate the receptors before desensitizing them, causing a temporary testosterone surge called “flare.” FIRMAGON achieves testosterone suppression within 3 days without this surge, which is particularly important for patients with symptomatic disease, impending spinal cord compression, or those who need rapid disease control.
The duration of FIRMAGON treatment is determined by your doctor based on your individual clinical situation. Treatment may continue for months to years depending on the stage of your prostate cancer, your response to therapy, and your overall treatment plan. For patients receiving FIRMAGON before and during radiotherapy, the treatment duration will be defined by the radiation treatment protocol. For advanced prostate cancer, treatment is typically continued for as long as it remains effective and tolerable.
No. FIRMAGON requires reconstitution from a powder and solvent before injection, and it must be administered as a deep subcutaneous injection. The reconstitution process requires careful technique to avoid foaming and ensure proper dissolution. For these reasons, FIRMAGON should always be administered by a trained healthcare professional (doctor or nurse) in a clinical setting. Your monthly injection appointment also provides an opportunity for your healthcare team to monitor your response to treatment.
All forms of androgen deprivation therapy carry some cardiovascular risk. FIRMAGON may affect heart rhythm (QT prolongation), which is why patients with pre-existing cardiovascular conditions or those taking QT-prolonging medications should be monitored carefully. However, some observational studies and pooled analyses have suggested that GnRH antagonists like degarelix may have a lower risk of cardiovascular events compared to GnRH agonists. Your doctor will assess your individual cardiovascular risk before starting treatment and monitor you accordingly.
Injection site reactions (pain, redness, swelling, hardening) are the most common side effect of FIRMAGON, particularly with the initial loading dose. These reactions are usually mild to moderate and resolve within a few days. Applying a cold compress to the injection site may help relieve discomfort. If reactions are severe, persistent, or show signs of infection (increasing warmth, spreading redness, pus), contact your healthcare provider promptly. Your provider will rotate injection sites within the abdominal area to minimize local reactions.
References
- European Medicines Agency (EMA). FIRMAGON – Summary of Product Characteristics. Available at: EMA EPAR. Last updated 2024.
- Klotz L, Boccon-Gibod L, Shore ND, et al. The efficacy and safety of degarelix: a 12-month, comparative, randomized, open-label, parallel-group phase III study. BJU International. 2008;102(11):1531-1538.
- Shore ND, Saad F, Cookson MS, et al. Oral relugolix for androgen-deprivation therapy in advanced prostate cancer. New England Journal of Medicine. 2020;382(23):2187-2196.
- European Association of Urology (EAU). Guidelines on Prostate Cancer. 2024 Edition. Available at: EAU Guidelines.
- National Comprehensive Cancer Network (NCCN). NCCN Clinical Practice Guidelines in Oncology: Prostate Cancer. Version 4.2024.
- Albertsen PC, Klotz L, Tombal B, et al. Cardiovascular morbidity associated with gonadotropin releasing hormone agonists and an antagonist. European Urology. 2014;65(3):565-573.
- World Health Organization (WHO). WHO Model List of Essential Medicines. 23rd List, 2023.
- British National Formulary (BNF). Degarelix. Available at: BNF Online.
About the Medical Editorial Team
This article was written and medically reviewed by the iMedic Medical Editorial Team, comprising board-certified physicians with specialization in oncology, urology, and clinical pharmacology. Our team adheres to the highest standards of evidence-based medicine and follows international guidelines from the European Association of Urology (EAU), National Comprehensive Cancer Network (NCCN), and European Medicines Agency (EMA).
All content is reviewed by at least two independent medical specialists. References are verified against peer-reviewed publications and regulatory authority databases.
We follow the GRADE framework for evaluating evidence quality. This article is based on Level 1A evidence from systematic reviews, randomized controlled trials, and regulatory authority assessments.
Last medical review: . Next scheduled review: January 2027. Our editorial standards are published at Editorial Standards.