Estradiol Transdermal System

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Estradiol Transdermal System contains NLT 85.0% and NMT 120.0% of the labeled amount of estradiol (C₁₈H₂₄O₂).

2 IDENTIFICATION

A. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

Procedure

Diluent: Acetonitrile and water (1:1)

Mobile phase: Acetonitrile and water (55:45)

Standard solution: 0.1 mg/mL of USP Estradiol RS in Diluent

Sample solutions: Equivalent to 0.1 mg/mL of estradiol in Diluent, prepared as follows. Cut 10 Transdermal Systems into pieces, and keep the pieces from each system separate. Remove and discard the protective liners, if present, from the strips. Transfer the pieces of each system into separate stoppered asks of suitable size, and add a measured volume of Diluent to each flask to provide the target estradiol concentration. Shake by mechanical means for about 3 h, and sonicate for 15 min.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 4.6-mm × 15-cm; packing L1

Column temperature: 35°

Flow rate: 1 mL/min

Injection size: 25 μL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: 0.9–1.6

Relative standard deviation: NMT 2.5%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of estradiol (C₁₈H₂₄O₂) in each Transdermal System taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of USP Estradiol RS in the Standard solution (mg/mL)

C_U = nominal concentration of estradiol in the Sample solution (mg/mL)

Use the individual assays to determine Uniformity of Dosage Units.

Acceptance criteria: 85.0%–120.0%

4 OTHER COMPONENTS

Alcohol Content (if present)

Diluent: Acetonitrile and water (1:1)

Internal standard solution: Prepare by diluting 4.0 mL of dehydrated methanol with water to 100 mL.

Standard stock solution: 5.0 mg/mL of Ethanol in Diluent. Prepare by weighing by difference 1.6 mL of dehydrated alcohol into a tared 50-mL volumetric flask containing 15 mL of water, and dilute with Diluent to volume. Pipet 10.0 mL of this solution into a 50-mL volumetric flask, and dilute with Diluent to volume.

Standard solution: 2.5 mg/mL of ethanol. Prepare by pipeting 25.0 mL of the Standard stock solution into a 50-mL volumetric flask. Add 5.0mL of the Internal standard solution, and dilute with water to volume.

Sample solutions: Prepare as directed for the Sample solutions in the Assay, with the following changes. Pipet 25.0 mL of each solution into individual 50-mL volumetric flasks. Add 5.0 mL of the Internal standard solution, and dilute with water to volume.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 2-mm × 2-m glass; support S2

Temperature

Column: 100°

Injection port: 200°

Detector: 200°

Carrier gas: Helium

Flow rate: 30 mL/min

Injection size: 2 μL

System suitability

Sample: Standard solution

[Note—The relative retention times for the methanol and alcohol peaks are 0.4 and 1.0, respectively.]

Suitability requirements

Relative standard deviation: NMT 1.5% from the peak response ratio of alcohol to methanol

Analysis

Samples: Standard solution and Sample solutions

Calculate the percentage of alcohol (C₂H₅OH) in each Transdermal System taken:

Result = (R_U/R_S) × (C_S/C_U) × 100

R_U = peak response ratio of alcohol to methanol from the Sample solution

R_S = peak response ratio of alcohol to methanol from the Standard solution

C_S = concentration of dehydrated alcohol in the Standard solution (mg/mL)

C_U = nominal concentration of alcohol in the Sample solution (mg/mL)

Average the percentage of alcohol found in the Transdermal Systems analyzed.

Acceptance criteria: 80%–120% of the labeled amount of C₂H₅OH

5 PERFORMANCE TESTS

Change to read:

Drug Release 〈724〉

Test 1: For products labeled for dosing every 84 h

Medium: Water; 900 mL, deaerated

Apparatus 5: 50 rpm

Times: 24, 48, and 96 h

Mobile phase: Water and acetonitrile (3:2)

Standard solution: 9 μg/mL of USP Estradiol RS in dehydrated alcohol. Dilute this solution with Medium to obtain solutions having concentrations of about 0.9, 0.45, and 0.045 μg/mL.

Sample solution: At each sampling time interval, withdraw a 10-mL aliquot of the solution under test.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Fluorimetric, with excitation at 220 nm and emission at 270 nm

Column: 4.6-mm × 3-cm; packing L1

Temperature: 40°

Flow rate: 1.0 mL/min

Injection size: 50 μL

System suitability

Sample: Standard solution

Tailing factor: 0.9–2.5

Relative standard deviation: NMT 3.0%, using 0.45 μg/mL of the Standard solution

Analysis: Plot the peak responses of the Standard solutions versus concentration, in μg/mL, of estradiol. From the graph determine the amount, in μg/mL, of estradiol released. Calculate the cumulative release rate as percentage of the labeled amount of estradiol:

At 24 h:

Result = {[900(A₁ − b)]/(1000 × m × L)} × 100

At 48 h:

Result = {[890(A₂ − b) + 10(A₁ − b]/(1000 × m × L)} × 100

At 96 h:

Result = {[880(A₃ − b) + 10(A₂ − b) + 10(A₁ − b)]/(1000 × m × L)} × 100

A₁ = peak area of estradiol in the Sample solution at the first time interval

A_n = peak area of estradiol in the Sample solution at the release interval n

m = slope of the calibration curve

b = y-intercept of the calibration curve

L = Transdermal System label claim (mg)

Tolerances: See Table 1.

Table 1

The percentages of the labeled amount of estradiol (C H O ) released at the times specified conform to Drug Release 〈724〉, Acceptance Table 1.

Test 2: If the product complies with this test, the labeling indicates that it meets USP Drug Release Test 2.

Medium: 0.005 M phosphate buffer, pH 5.5, containing 0.3% sodium lauryl sulfate; 500 mL

Apparatus 5: 100 rpm. Use a 76-mm stainless steel disk assembly. Adhere the patch to the disk assembly using transfer tape. [Note—A suitable tape is available as 3M adhesive transfer tape 927, www.mmm.com.]

Times: 1, 4, 8, and 24 h

Mobile phase: Acetonitrile and water (1:1)

Standard stock solution: 800 μg/mL of USP Estradiol RS in acetone

Standard solution: Dilute the Standard stock solution with Medium to obtain a solution having a known concentration close to that expected in the solution under test, assuming 100% drug release.

Sample solution: At each sampling time interval, withdraw a known volume aliquot of the solution under test.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 205 nm

Column: 3.9-mm × 30-cm; packing L1

Flow rate: 1.0 mL/min

Injection size: 100 μL

System suitability

Sample: Standard solution

Tailing factor: NMT 2.0

Relative standard deviation: NMT 3.0%

Analysis: Calculate the amount of estradiol released at each sampling time:

M_i = (r_U/r_S) × C_S × V_i

m₁ = M₁

m₂ = M₂ + M₁(V_a/V₁)

m₃ = M₃ + M₂(V_a/V₂) + M₁(V_a/V₁)

m₄ = M₄ + M₃(V_a/V₃) + M₂(V_a/V₂) + M₁(V_a/V₁)

Calculate the percentage of the labeled amount of estradiol released at each sampling time:

Result = (m_i/L) × 100

M_i = amount of estradiol released into the Medium at a given sampling time (mg)

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of the Standard solution (mg/mL)

V_i = corrected volume of the Medium at a given sampling time (mL)

m₁ , m₂ , m₃ , m₄ = total amounts of estradiol released from the patch at given sampling times (mg)

M₁, M₂, M₃, M₄ = amounts of estradiol released into the Medium at given sampling times (mg)

V_a = volume of the aliquot taken from the dissolution vessel at each sampling time (mL)

V₁ , V₂ , V₃ = volumes of Medium at given sampling times (mL)

L = Transdermal System label claim (mg)

Tolerances: See Table 2.

Table 2

The percentages of the labeled amount of estradiol (C₁₈H₂₄O₂) released at the times specified conform to Drug Release 〈724〉, Acceptance

Table 1.

Test 3: If the product complies with this test, the labeling indicates that it meets USP Drug Release Test 3.

Medium: 1% (v/v) polysorbate 40 in water; 900 mL

Apparatus 5: 50 rpm

Times: 4, 8, and 24 h

Standard stock solution: Known concentration (mg/mL) of USP Estradiol RS in methanol

Standard solution: Five different concentrations within the range of the expected release amounts of estradiol, prepared as follows. Add 1.0mL of polysorbate 40 into a 100-mL volumetric flask, and then add the required amount of Standard stock solution. Mix well to dissolve the polysorbate 40, and dilute with water to volume.

Sample solution: At each sampling time interval, withdraw a known volume aliquot of the solution under test.

Mobile phase: Acetonitrile and water (2:3)

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.6-mm × 15-cm, 5-μm packing L1 for 9-cm2

systems; 4.6-mm × 12.5-cm, 5-μm packing L1 for 18-, 27-, or 36-cm2

systems. In any

case, a guard column containing packing L1 is used.

Flow rate: 1.0 mL/min

Injection size: 50 μL

System suitability

Sample: Standard solution

Relative standard deviation: NMT 2.0%

Analysis: Calculate the cumulative release rate as a percentage of the labeled amount of estradiol:

Result = {[900(A − b)]/(1000 × m × L)} × 100

A = peak area of estradiol in the Sample solution at each time interval

b = y-intercept of the calibration curve

m = slope of the calibration curve

L = Transdermal System label claim (mg)

Tolerances: The percentages of the labeled amount of estradiol (C₁₈H₂₄O₂) released at the times specified conform to Table 3, Table 4, and Table 5.

L1 (6 units)

Table 3

L2 (12 units)

Table 4

L3 (24 units)

Table 5

Test 4: If the product complies with this test, the labeling indicates that it meets USP Drug Release Test 4.

Medium: Water; 500 mL for 0.025 mg/day and 0.0375 mg/day dosage; 900 mL for 0.05 mg/day, 0.075 mg/day, and 0.1 mg/day dosage

Apparatus 6: 50 rpm. Use a stainless steel cylinder assembly. Adhere the Transdermal System to the cylinder assembly using a strip of suitable double-sided transfer tape.

Times: 2, 6, and 12 h

Buffer solution: 25 mM of monobasic sodium phosphate, adjusted with phosphoric acid to a pH of 3.0

Mobile phase: Acetonitrile and Buffer solution (40:60)

Standard stock solution: 0.2 mg/mL of USP Estradiol RS in methanol

Standard solution: Dilute the Standard stock solution with Medium to obtain a solution having a known concentration that is approximately 90% of the concentration expected from complete release in the solution under test.

Sample solution: At each sampling time interval, withdraw about 1.5 mL of the solution under test. Place each sample aliquot into an amber HPLC vial.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 3.0-mm × 10-cm; 3.5-μm packing L1

Flow rate: 0.5 mL/min

Injection volume: 15 μL

Run time: 2.5 times the retention time of estradiol

System suitability

Sample: Standard solution

Tailing factor: NMT 1.8

Relative standard deviation: NMT 3.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the concentration (C_i) of estradiol (C₁₈H₂₄O₂) in the sample withdrawn from the vessel at time point i:

C_i = (r_i /r_S) × C_S

r_i = peak response of estradiol from the Sample solution at time point i

r_S = peak response of estradiol from the Standard solution

C_S = concentration of USP Estradiol RS in the Standard solution (mg/mL)

Calculate the percentage of the labeled amount of estradiol (C₁₈H₂₄O₂) released at each time point (i):

Result₁ = C₁ × V × (1/L) × 100

Result₂ = {[C₂ × (V − V_S)] + (C1 × V_S)} × (1/L) × 100

Result₃ = ({C₃ × [V − (2 × V_S)]} + [(C₂ + C₁) × V_S]) × (1/L) × 100

C_i = concentration of estradiol in the portion of the sample withdrawn at each time point (i) (mg/mL)

V = volume of Medium, 900 or 500 mL

L = Transdermal System label claim (mg)

V_S = volume of Sample solution withdrawn from the Medium (mL)

Tolerances: See Table 6.

Table 6

The percentages of the labeled amount of estradiol (C H O ) released at the times specified conform to Dissolution 〈711〉, Acceptance

Table 2.

Test 6: If the product complies with this test, the labeling indicates that it meets USP Drug Release Test 6.

Medium: Water; 500 mL for 0.025 and 0.0375 mg/day dosages; 900 mL for 0.05, 0.075, and 0.1 mg/day dosages

Apparatus 6: 50 rpm. Use a stainless steel cylinder assembly. Adhere the Transdermal System to the bottom of the cylinder by using a suitable adhesive.

Times: 1, 4, 8, and 12 h

Mobile phase: Acetonitrile and water (60:40)

Diluent: Absolute alcohol and water (50:50)

Standard stock solution: 500 μg/mL of USP Estradiol RS in absolute alcohol prepared as follows. Transfer a suitable amount of USP

Estradiol RS to a suitable volumetric flask, add absolute alcohol to 50% of the flask volume, and sonicate to dissolve. Dilute with absolute alcohol to volume.

Standard solution: Dilute the Standard stock solution with Diluent to obtain a solution with a known concentration that is approximately 80% of the concentration expected from complete release in the solution under test.

Sample solution: Accurately transfer 4.0 mL of absolute alcohol as a stabilizer to each sample tube prior to sampling. At each sampling time interval, withdraw about 4.0 mL of the solution under test, and pass through a suitable filter of 10-μm pore size. Mix 4.0 mL of the filtered test solution with 4.0 mL of absolute alcohol in the sample tube.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 220 nm

Column: 4.6-mm × 15-cm; 3.5-μm packing L1

Flow rate: 1.0 mL/min

Injection volume: 50 μL

Run time: 4.5 times the retention time of estradiol

System suitability

Sample: Standard solution

Tailing factor: NMT 2.0

Relative standard deviation: NMT 3.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the concentration (C_i) of estradiol (C₁₈H₂₄O₂) in the sample withdrawn from the vessel at time point i:

C_i = (r_i/r_S) × C_S × D

r_i = peak response of estradiol from the Sample solution at time point i

r_S = peak response of estradiol from the Standard solution

C_S = concentration of USP Estradiol RS in the Standard solution (mg/mL)

D = dilution factor, 2

Calculate the percentage of the labeled amount of estradiol (C₁₈H₂₄O₂) released at each time point (i):

Result₁ = C₁ × V₁ × (1/L) × 100

Result₂ = {[C₂ × (V − V_S)] + (C₁ × V_S)} × (1/L) × 100

Result₃ = ({C₃× [V − (2 × V_S)]} + [(C₂ +C₁) × V_S]) × (1/L) × 100

Result₄ = ({C₄ × [V − (3 × V_S)]} + [(C₃ + C₂+ C₁) × V_S]) × (1/L) × 100

C_i = concentration of estradiol in the portion of the sample withdrawn at each time point (i) (mg/mL)

V = volume of Medium, 900 or 500 mL

L = Transdermal System label claim (mg)

V_S = volume of Sample solution withdrawn from the Medium (mL)

Tolerances: See Table 7.

Table 7

The percentages of the labeled amount of estradiol (C₁₈H₂₄O₂) released at the times specified conform to Drug Release 〈724〉, Acceptance

Table 1. (RB 1-Dec-2019)

Uniformity of Dosage Units 〈905〉: The results from the Transdermal Systems used in the Assay meet the requirements.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in hermetic, light-resistant, unit-dose pouches.

Labeling: The label states the total amount of estradiol in the Transdermal System and the release rate, in mg/day, for the duration of application of one system. When more than one Drug Release test is given, the labeling states the Drug Release test used only if Test 1 is not used.

USP Reference Standards 〈11〉

USP Estradiol RS