에스트라디올 운데실레이트 (EU)

雌激素 C

Estradiol Undecylate Injection

Estradiol Undecylate (EU)

Intramuscular (IM)

Estradiol undecylate (EU) is one of the longest-acting injectable estradiol esters, with a half-life of approximately 20-30 days, allowing for monthly or longer injection intervals ^[1] . Formerly sold as Progynon Depot 100 and other brands, global availability is now very limited. Evidence level is C due to the lack of large-scale HRT clinical trial data.

Pharmacokinetics

Pharmacokinetic profile of estradiol undecylate ^{[1] [2]} :

• Half-life: ~20-30 days (longest of all injectable esters)
• Peak time: ~3-7 days post-injection
• Duration of action: A single injection maintains effective E2 levels for ~30-40 days
• Steady state: Due to the very long half-life, requires ~2-3 months to reach steady state

Comparison with Other Injectable Esters

Parameter	EV (Valerate)	EC (Cypionate)	EU (Undecylate)
Half-life	~4-5 days	~8-10 days	~20-30 days
Injection interval	5-7 days	7-14 days	21-30 days
Dose adjustment flexibility	High	Moderate	Low
Serum level fluctuation	Larger	Moderate	Smaller
Global availability	Widely available	Americas	Very limited
Evidence level	A	B	C

Evidence Level C

Clinical data on estradiol undecylate in transgender HRT is very limited. Most pharmacokinetic data comes from small studies conducted in the 1970s-1980s. When other injectable esters (EV or EC) are available, they are generally recommended as first-line options with stronger evidence.

Dosing

Adult Dosing (Reference Only)

Phase	Dose	Notes
Starting dose	20-40 mg/month	Conservative start
Maintenance dose	40-100 mg/month	Adjust based on trough E2
Maximum dose	100 mg/month	Do not exceed

Due to its very long half-life, EU dose adjustments are slow to take effect. For situations requiring rapid level adjustment, shorter-acting esters (EV) are more appropriate ^[3] .

Brands & Availability

Brand	Concentration	Region	Status
Progynon Depot 100	100 mg/mL	Formerly Europe/Asia	Discontinued
Compounding pharmacies	Various	Very few regions	Limited

EU has extremely limited global availability. Most users should choose EV or EC as their preferred injectable estradiol.

Monitoring

• E2: Every 3 months, trough draw 1-2 days before injection. Target 100-200 pg/mL
• T: Every 3 months. Target <50 ng/dL
• Liver function (ALT/AST): Baseline + every 6 months

Due to the very long half-life, more frequent blood monitoring is needed during initial use to confirm accumulation levels.

Safety Limits

• EU’s ultra-long half-life means higher accumulation risk — if side effects occur, the drug will remain in the body for weeks after discontinuation
• Not suitable for situations requiring rapid dose adjustment
• E2 >200 pg/mL does not produce stronger feminization ^[3]
• Due to extremely unstable global supply, EU is not recommended as a primary HRT regimen