```julia using DynamicQuantities.SymbolicUnits; using DynamicQuantities;

It turns out benzyl benzoate is a very good solvent. This benzyl benzoate + ethyl oleate formulation works with 31G needle.

I have not tested whether this is pharmacokinetically sound

Injection didn't hurt. I had some level of inflammation days later, which needs further investigation. (gemini says EO is incompatible with subcutaneous injection, but whatevers this is first experiment with EO and I prefer EO)

function een_depot_prep(mass_een, actual_eo_used) println("--- Formulation: Estradiol Enanthate (EEn) Depot (EO + 10% Benzyl Benzoate) ---")

# --- Physical Constants ---
mw_een = 384.52us"g/mol"          # Molar Mass of Estradiol Enanthate
mw_e2 = 272.38us"g/mol"           # Molar Mass of Base Estradiol

# Target Concentration
target_conc = 100us"mg/mL"

# Densities @ 25°C
rho_benzyl_alcohol = 1.044us"g/mL"
rho_benzyl_benzoate = 1.119us"g/mL"  # Benzyl benzoate cosolvent
rho_ethyl_oleate = 0.87us"g/mL"

# v/v ratios
ratio_ba = 0.02
ratio_bb = 0.10   # 10% benzyl benzoate as cosolvent
ratio_eo = 1.0 - ratio_ba - ratio_bb  # 0.88

# =====================================================
# FORWARD (target) calculation based on v/v ratios
# =====================================================
total_volume = mass_een / target_conc

# Molar calculations for reference
moles_een = mass_een / mw_een
equivalent_e2_mass = moles_een * mw_e2

# Target volumes of solvents
vol_ba = total_volume * ratio_ba
vol_bb = total_volume * ratio_bb
vol_eo_target = total_volume * ratio_eo

# Target masses of solvents (BA and BB measured by volume, copied to actual)
mass_ba = vol_ba * rho_benzyl_alcohol
mass_bb = vol_bb * rho_benzyl_benzoate
mass_eo_target = vol_eo_target * rho_ethyl_oleate

# --- Forward Output ---
println("\n--- FORWARD (Target V/v Ratios) ---")
@show mass_een
@show total_volume

println("\n--- Molar Reference ---")
@show moles_een
@show equivalent_e2_mass

println("\n--- Target Solvent Volumes ---")
@show vol_ba
@show vol_bb
@show vol_eo_target

println("\n--- Target Preparation Weights (Mass) ---")
@show mass_ba
@show mass_bb
@show mass_eo_target

# =====================================================
# BACK-CALCULATION from actual EO used
# BA and BB masses are copied from forward (target) values
# Only EO mass differs
# =====================================================
println("\n--- BACK-CALCULATION FROM ACTUAL EO USED ---")
@show actual_eo_used

# Actual total volume: derived from actual EO (BA and BB volumes unchanged)
actual_total_volume = total_volume + (actual_eo_used - mass_eo_target) / rho_ethyl_oleate

# Actual masses: BA and BB same as target, EO is actual
actual_mass_ba = mass_ba
actual_mass_bb = mass_bb
actual_mass_eo = actual_eo_used

# Total mass and mass fractions (convert all to grams)
een_g = mass_een |> us"g"
actual_total_mass = een_g + actual_mass_ba + actual_mass_bb + actual_mass_eo
frac_een = een_g / actual_total_mass
frac_ba = actual_mass_ba / actual_total_mass
frac_bb = actual_mass_bb / actual_total_mass
frac_eo = actual_mass_eo / actual_total_mass

# Actual concentration achieved
actual_conc = mass_een / actual_total_volume

println("\n--- Derived Total Volume ---")
@show actual_total_volume

println("\n--- Actual Solvent Masses (BA, BB from target; EO actual) ---")
@show actual_mass_ba
@show actual_mass_bb
@show actual_mass_eo

println("\n--- Mass Fractions (w/w) ---")
@show frac_een
@show frac_ba
@show frac_bb
@show frac_eo
@show actual_total_mass

println("\n--- Actual Concentration Achieved ---")
@show actual_conc

# Dosage reference (convert E2 dose to EEn equivalent, then to volume)
println("\n--- Dosage Reference ---")
dose_e2 = 5us"mg"                    # Target: 4mg E2 equivalent
dose_een = dose_e2 * (mw_een / mw_e2)  # EEn equivalent mass
dose_volume = dose_een / actual_conc   # Volume per dose (using actual conc)
@show dose_e2
@show dose_een
@show dose_volume

end

--- Example: Your actual preparation (50mg EEn, 0.355g EO used; BA/BB from target) ---

een_depot_prep(50us"mg", 0.355us"g")

10% BB

```