Half-Life of Triptorelin
The half-life of triptorelin varies by route of administration, with a biological half-life approximately 3-5 hours when administered parenterally. 1
Pharmacokinetic Properties
Triptorelin (also known as triptorelin pamoate or embonate) is a synthetic gonadotropin-releasing hormone (GnRH) agonist with specific pharmacokinetic characteristics:
- Distribution half-life: Approximately 40 minutes 2
- Elimination half-life: Approximately 4.5 hours 2
- Biological half-life: 10 times greater when administered subcutaneously compared to intravenous injection due to progressive release from the injection site 1
Formulations and Sustained Release
Triptorelin is available in several sustained-release formulations that significantly extend its clinical effect beyond its basic half-life:
- Monthly formulation: 3.75 mg (administered every 28 days) 3
- 3-month formulation: 11.25 mg
- 6-month formulation: 22.5 mg (administered every 24 weeks) 4
These sustained-release formulations were developed to offer greater convenience to both patients and physicians by reducing injection frequency while maintaining therapeutic efficacy 4.
Pharmacodynamic Effects
Despite its relatively short half-life, triptorelin's clinical effects are prolonged due to its mechanism of action:
- Initially stimulates luteinizing hormone (LH) and testosterone secretion
- Subsequently causes suppression of these hormones
- Achieves castration levels of testosterone (≤50 ng/dL) in 91.2% of patients by day 29 3
- Maintains castration in 97.7% of patients by day 57 3
Clinical Significance of Half-Life
The pharmacokinetic profile of triptorelin offers several advantages:
- Compared to other GnRH agonists like leuprolide, triptorelin has a slightly slower onset of action but maintains castration equally effectively 3
- The sustained efficacy even after one or two days of withdrawal provides an advantage over GnRH antagonists, whose effect disappears as soon as administration is stopped 1
- The long-acting formulations reduce the need for frequent injections, improving patient compliance and quality of life 5
Metabolism and Elimination
Triptorelin undergoes metabolic breakdown in the body:
- A unique in vivo metabolite, triptorelin (5-10), has been identified in urine and serum 6
- This metabolite can be detected even when parent triptorelin levels are undetectable 6
Understanding triptorelin's half-life is crucial for appropriate dosing and monitoring in clinical practice, particularly in the treatment of prostate cancer and other conditions requiring hormonal manipulation.