Relugolix Dosing for Advanced Prostate Cancer and Uterine Fibroids
Advanced Prostate Cancer
For advanced prostate cancer, relugolix (ORGOVYX) is dosed as a 360 mg loading dose on day 1, followed by 120 mg once daily thereafter. 1
Dosing Details
- Loading dose: 360 mg orally on the first day of treatment 1
- Maintenance dose: 120 mg orally once daily starting on day 2 1
- Administration: Can be taken with or without food, as no clinically meaningful differences in pharmacokinetics were observed with high-fat meals 1
Efficacy Timeline
- Rapid castration: 56% of patients achieved castrate testosterone levels (<50 ng/dL) by day 4, with 97% maintaining castration through 48 weeks 1
- Sustained suppression: In the HERO trial, relugolix achieved 96.7% sustained castration rates compared to 88.8% with leuprolide 2, 3
Special Populations
- No dose adjustment needed for age (45-91 years), mild to severe renal impairment (CrCl 15-89 mL/min), or mild to moderate hepatic impairment (Child-Pugh A or B) 1
- Not studied in end-stage renal disease requiring hemodialysis or severe hepatic impairment (Child-Pugh C) 1
Combination Therapy Considerations
- When combined with abiraterone: Standard relugolix dose (120 mg daily) is used with abiraterone 1,000 mg daily plus corticosteroid 4
- When combined with apalutamide: A higher dose of relugolix (240 mg daily) was studied with apalutamide 240 mg daily, though standard dosing remains 120 mg 4
- Radiotherapy: Standard dosing (120 mg daily after 360 mg loading) is used with concurrent radiotherapy for both short-term (24 weeks) and longer-term (48 weeks) ADT 2
Uterine Fibroids
For uterine fibroids, relugolix is dosed as 40 mg once daily in combination with estradiol 1 mg and norethindrone acetate 0.5 mg (relugolix combination therapy). 5, 6
Dosing Details
- Fixed-dose combination: 40 mg relugolix + 1 mg estradiol + 0.5 mg norethindrone acetate taken once daily 6
- No loading dose required for the fibroid indication 6
- Duration: Studied for 24 weeks in the LIBERTY trials, with demonstrated efficacy in reducing heavy menstrual bleeding and fibroid symptoms 6
Rationale for Combination Therapy
- Bone preservation: The addition of estradiol and norethindrone acetate prevents bone mineral density loss that occurs with relugolix monotherapy 5, 6
- Hypoestrogenic symptom mitigation: Combination therapy reduces hot flushes, headaches, and other hypoestrogenic effects while maintaining efficacy 5
Efficacy
- Primary endpoint: 73% (LIBERTY 1) and 71% (LIBERTY 2) of patients achieved menstrual blood loss <80 mL with ≥50% reduction from baseline, compared to 19% and 15% with placebo 6
- Quality of life: Significant improvements in symptom severity scores (-33.5 vs -12.1 with placebo) and health-related quality of life (+37.6 vs +13.1 with placebo) at 24 weeks 7, 6
Critical Drug Interactions
Avoid or Use with Caution
- Combined P-gp and moderate CYP3A inhibitors (e.g., erythromycin): Increase relugolix exposure by 3.5-fold for AUC and 2.9-fold for Cmax 1
- Combined P-gp and strong CYP3A inducers (e.g., rifampin): Decrease relugolix exposure by 55% for AUC and 23% for Cmax, potentially reducing efficacy 1
No Clinically Significant Interactions
- Strong CYP3A inhibitors alone (voriconazole), atorvastatin, enzalutamide, or acid-reducing agents do not significantly affect relugolix pharmacokinetics 1
- Cardiovascular medications (antihypertensives, antithrombotics, lipid-modifying agents) do not impact relugolix efficacy or substantially alter safety profile 8, 9
Key Safety Considerations
Cardiovascular Benefits (Prostate Cancer)
- 54% reduction in major adverse cardiovascular events compared to leuprolide in the HERO trial, making relugolix particularly advantageous for patients with cardiovascular comorbidities 8, 3
Testosterone Recovery (Prostate Cancer)
- Rapid recovery: 55% of patients achieved testosterone >280 ng/dL or baseline levels at 90 days post-discontinuation, compared to 16% with degarelix 1, 3
- Mean testosterone levels 90 days post-treatment: 310.5 ng/dL (relugolix) vs 53.0 ng/dL (leuprolide) 2