FertirelinvsLeuprolide

Molecular Formula

C₅₅H₇₆N₁₆O₁₂

Molecular Weight

1153.3 g/mol

Half-Life

Variable depending on formulation; sustained-release formulations extend duration

Bioavailability

High when administered via injection

CAS Number

66002-66-2

Molecular Formula

C₅₉H₈₄N₁₆O₁₂

Molecular Weight

1209.4 g/mol

Half-Life

Approximately 2-6 hours (varies by route of administration)

Bioavailability

~95% (subcutaneous injection)

CAS Number

74381-53-6

Common

• Mild discomfort at treatment site
• Transient hormone fluctuations
• Temporary behavioral changes in animals
• Mild injection site reactions
• Short-term changes in appetite
• Temporary mood variations
• Minimal systemic effects at therapeutic doses

Uncommon

• Occasional swelling at injection site

Serious

• Severe allergic reaction

Common

• Hot flashes (very common in men)
• Decreased libido and erectile dysfunction
• Injection site pain or swelling
• Nausea
• Fatigue
• Mood changes or depression
• Joint or muscle pain
• Headaches
• Dizziness
• Thinning hair
• Decreased bone density (osteoporosis with long-term use)
• QT prolongation (rare but serious cardiac effect)
• Tumor flare (temporary worsening of cancer symptoms in first weeks)
• Severe allergic reactions
• Spinal cord compression risk in men with metastatic disease

Serious

• Severe allergic reaction

Evidence Level

Moderate human trials (Phase 1-2)

FDA Status

Research compound

Safety Overview

Fertirelin is a GnRH agonist developed specifically for veterinary use in livestock, particularly cattle breeding and fertility management. The peptide has been safely used in veterinary medicine for over 40 years with a well-documented safety profile in animals. Important limitation: Fertirelin is NOT approved for human use. All safety and efficacy data comes from veterinary applications in cattle and limited laboratory research. Human safety data is minimal and extrapolation from veterinary use is problematic. The biphasic response (initial hormone surge followed by suppression) must be carefully managed in any application. Individual responses can vary significantly based on age, hormonal status, and concurrent medications.

Contraindications

• xPregnancy (may disrupt existing pregnancy)
• xHypersensitivity to GnRH analogs
• xActive reproductive infections
• xConcurrent use with certain medications
• xUndiagnosed reproductive disorders

Evidence Level

Strong human trials (Phase 3 or FDA approved)

FDA Status

FDA approved for this use

Safety Overview

Leuprolide (Lupron) is an FDA-approved GnRH agonist with 35+ years of clinical safety data involving millions of patients in oncology and endocrinology. The critical safety issue is the initial 5-7 day flare effect—temporary surge in FSH/LH causing symptom worsening before hormone suppression begins—particularly dangerous for prostate cancer patients (flare can cause urinary obstruction or spinal cord compression). Bone density loss is a dose-dependent long-term risk in both men and women requiring monitoring. Injection site reactions, hot flushes, and initial hypogonadal symptoms are expected and typically transient.

Contraindications

• xPregnancy or breastfeeding (teratogenic)
• xUndiagnosed vaginal bleeding
• xActive bone metastases with spinal cord compression (increased fracture risk)
• xAllergy to GnRH agonists or components
• xSevere cardiovascular disease with QT prolongation risk