What Is Histrelin (Vantas<sup>®</sup>)?
Vantas® (histrelin) is a Gonadotropin Releasing Hormone (GnRH) agonist (or LHRH agonist). It is indicated for use as a palliative treatment option for individuals with advanced prostate cancer. Vantas is administered as a subcutaneous (under the skin) implant, delivered through an incision in the upper arm, that lasts for 12 months. Individuals taking Vantas 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 in treatment that can lead to spinal cord compression and other adverse effects. Individuals taking Vantas should also be monitored for high blood sugar and the development of diabetes, as well as for cardiovascular complications.
How does Vantas work?
Vantas’ 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. Vantas 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 making 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 Vantas.
What are the possible side effects of Vantas?
Multiple clinical trials evaluated the safety and efficacy of Vantas. The most common side effects of Vantas in men include hot flashes, fatigue, urination problems, erectile dysfunction, constipation, breast enlargement, and shrinking of the testicles. Implant site reactions are also possible while receiving Vantas. This is not an exhaustive list of all potential side effects of Vantas. Talk to your healthcare provider or pharmacist for further information.
Things to note about Vantas
Several rare but more serious side effects can accompany Vantas including Tumor Flare Phenomenon, increased blood sugar, and difficulty locating or removing the implant. Additionally, Vantas 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 Vantas should be monitored for any cardiovascular concerns. Vantas may also cause a decrease in bone mineral density, leading to osteoporosis (thinning of the bones).
Tumor Flare Phenomenon is possible while taking Vantas, 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 implantation site injury while taking Vantas. Alert your provider immediately if you notice unusual pain, redness, or bleeding at the insertion site.
Before starting Vantas talk to your provider if you:
- Have any heart or vascular 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
- Are taking any other medications (prescription and over-the-counter), vitamins, or herbal supplements
Vantas is implanted by a physician in your upper arm. The implant contains 50 mg of histrelin acetate, and will deliver 41 mg of histrelin to your body over 12 months. Patients should talk to their doctor if they have any questions, or if they have questions regarding their Vantas regimen.1
These are not all the possible side effects of histrelin. Patients should talk to their doctor about what to expect with treatment with histrelin.