Estradiol Cypionate (EC)
Estradiol Cypionate Injection
Estradiol Cypionate (EC)
Intramuscular (IM) / Subcutaneous (SC)
Estradiol cypionate (EC) is a long-acting injectable estradiol ester, primarily used in the Americas. Compared to estradiol valerate (EV), EC has a longer half-life (~8-10 days vs 4-5 days), allowing for extended injection intervals [1] . Brand name: Depo-Estradiol.
Pharmacokinetics
Section titled “Pharmacokinetics”Pharmacokinetic profile of estradiol cypionate [1] [2] :
- Half-life: ~8-10 days (vs ~4-5 days for EV)
- Peak time: 2-4 days post-injection
- Trough time: 7-10 days post-injection
- Steady state: Reached after ~3-4 regular cycles
Comparison with Estradiol Valerate (EV)
Section titled “Comparison with Estradiol Valerate (EV)”| Parameter | Estradiol Cypionate (EC) | Estradiol Valerate (EV) |
|---|---|---|
| Half-life | ~8-10 days | ~4-5 days |
| Peak time | 2-4 days | 2-3 days |
| Recommended interval | 7-14 days | 5-7 days |
| Serum level fluctuation | Smaller | Larger |
| Primary region | Americas | Global |
| VTE risk (RR) | ~1.0 (bypasses first-pass) | ~1.0 |
| Evidence level | B | A |
The longer half-life of EC results in less E2 decline at trough, producing a smoother concentration curve [3] .
Dosing
Section titled “Dosing”Adult Dosing
Section titled “Adult Dosing”| Phase | Dose | Notes |
|---|---|---|
| Starting dose | 2-3 mg/week | Low-dose start (first 1-6 months) to protect breast development |
| Maintenance dose | 3-5 mg/week | Adjust based on trough E2; target 100-200 pg/mL |
| Maximum dose | 7 mg/10-14 days | Do not exceed |
Dosing references: Endocrine Society 2017 [4] and WPATH SOC 8 [5] . Due to EC’s longer half-life, some users opt for 10-14 day injection intervals.
Brands & Availability
Section titled “Brands & Availability”| Brand | Concentration | Region |
|---|---|---|
| Depo-Estradiol | 5 mg/mL | United States |
| Compounding pharmacies | Various | Select regions |
EC is primarily available in the US and Latin America. In regions where it is unavailable, estradiol valerate injection is the standard alternative.
Monitoring
Section titled “Monitoring”Same as other injectable estradiol esters:
- E2: Every 3 months, trough draw (morning before injection). Target 100-200 pg/mL
- T: Every 3 months. Target <50 ng/dL
- Liver function (ALT/AST): Baseline + every 6 months
Injection Technique
Section titled “Injection Technique”Injection procedure is identical to estradiol valerate injection. Both SC and IM routes are suitable.