Estradiol Undecylate (EU)
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
Section titled “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
Section titled “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 |
Dosing
Section titled “Dosing”Adult Dosing (Reference Only)
Section titled “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
Section titled “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
Section titled “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.