What are the approved indications, dosing regimens, contraindications, common adverse effects, and monitoring recommendations for relugolix?

Relugolix: Clinical Overview

Approved Indications

Relugolix (ORGOVYX) is FDA-approved for the treatment of adult patients with advanced prostate cancer [1, 1. In the EU, it is indicated specifically for advanced hormone-sensitive prostate cancer 2. Additionally, when combined with estradiol and norethindrone acetate as a fixed-dose combination, relugolix is FDA-approved for fibroid-related heavy menstrual bleeding [3, 3.

Dosing Regimens

For Prostate Cancer:

• Loading dose: 360 mg orally on Day 1
• Maintenance: 120 mg orally once daily at approximately the same time each day
• Can be taken with or without food
• Swallow tablets whole—do not crush or chew [1, 1

Missed Dose Management:

• If missed by ≤12 hours: Take as soon as remembered
• If missed by >12 hours: Skip and resume next scheduled dose
• If treatment interrupted >7 days: Restart with 360 mg loading dose, then continue 120 mg daily 1

Dose Modifications:

With P-gp Inhibitors:

• Avoid co-administration if possible
• If unavoidable: Take relugolix first, separate dosing by ≥6 hours
• May interrupt treatment up to 2 weeks for short-course P-gp inhibitor 1

With Combined P-gp and Strong CYP3A Inducers:

• Avoid co-administration if possible
• If unavoidable: Increase dose to 240 mg once daily
• Resume 120 mg daily after inducer discontinuation 1

For Uterine Fibroids:

Relugolix is used as second-line medical management (after NSAIDs, oral contraceptives, and tranexamic acid) for fibroid-related heavy menstrual bleeding. Combination therapy with low-dose estrogen and progestin is FDA-approved and mitigates hypoestrogenic effects [3, 3.

Contraindications

Relugolix is contraindicated in patients with severe hypersensitivity to relugolix or any product components [1, 1. This includes patients who have experienced angioedema or pharyngeal edema with prior exposure.

Common Adverse Effects

Most common adverse reactions (≥10%):

• Hot flushes (57% in prostate cancer trials) [1, 1, 4
• Musculoskeletal pain
• Fatigue
• Constipation
• Diarrhea

Laboratory Abnormalities (≥15%):

• Increased glucose
• Increased triglycerides
• Decreased hemoglobin
• Elevated ALT and AST [1, 1

Hypoestrogenic Effects (as monotherapy):

• Headaches
• Hot flushes
• Hypertension
• Loss of bone mineral density [3, 3

Important Safety Considerations:

• Hypersensitivity reactions including angioedema reported in 0.2% of patients 1
• Generally well-tolerated with mostly grade 1-2 adverse events [2, 5
• Injection site reactions avoided compared to injectable GnRH antagonists 6

Monitoring Recommendations

Cardiovascular Monitoring:

Consider periodic ECG and electrolyte monitoring, particularly in patients with:

• Congenital long QT syndrome
• Congestive heart failure
• Frequent electrolyte abnormalities
• Concurrent QT-prolonging medications 1

Correct electrolyte abnormalities before and during treatment 1. Notably, relugolix demonstrated a 54% reduction in major adverse cardiovascular events compared to leuprolide in the HERO trial [7, [2, 8, 5.

Hormonal and Oncologic Monitoring:

• Monitor PSA levels periodically to assess therapeutic effect 1
• If PSA increases, measure serum testosterone concentrations 1
• Therapy results in suppression of pituitary-gonadal system; diagnostic tests of pituitary gonadotropic and gonadal function may be affected during and after treatment 1

Efficacy Benchmarks:

• 56% of patients achieve castrate testosterone levels (<50 ng/dL) by Day 4
• 97% maintain castrate levels through 48 weeks 1
• Median time to castration: 4 days 4
• Castration rates: 95% at <1.73 nmol/L threshold 4

Testosterone Recovery:

After discontinuation, 55% of patients achieve testosterone >280 ng/dL or baseline at 90 days 1. In comparative studies, 52% on relugolix vs 16% on degarelix experienced testosterone recovery at 3 months [8, 4.

Key Clinical Advantages

Relugolix offers several advantages over traditional GnRH agonists:

• No initial testosterone flare (unlike GnRH agonists) [2, 6, 5
• Rapid testosterone suppression (median 4 days) [1, 4
• Oral once-daily administration (patient-friendly vs injections) [2, 6
• Superior cardiovascular safety profile (54% reduction in major adverse cardiac events vs leuprolide) [7, 2, 8, 5
• Faster testosterone recovery after discontinuation [8, 4, 5

Important Caveats

• Fertility is suppressed during treatment; rapid symptom recurrence after cessation [3, 3
• Embryo-fetal toxicity: Males with female partners of reproductive potential must use effective contraception during treatment and for 2 weeks after last dose 1
• Safety and efficacy not established in females (for prostate cancer indication) 1
• Treatment continuation is typical upon development of castration-resistant prostate cancer 1