Levothyroxine Sodium Tablets

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

Levothyroxine Sodium Tablets contain NLT 95.0% and NMT 105.0% of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄).

2 IDENTIFICATION

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

3 ASSAY

Procedure

[Note—Use Sample solution 2 for Tablets labeled to meet the requirements of Dissolution Test 3. For all other products, use the Sample solution.]

Mobile phase: Acetonitrile and water (4:6) containing 0.5 mL of phosphoric acid per liter of mixture

Solution A: Dissolve 400 mg of sodium hydroxide in 500 mL of water. Cool, and add 500 mL of methanol.

Diluent: Methanol and water (6:4) containing 0.5 mL of phosphoric acid per liter of mixture

Levothyroxine stock solution: 0.4 mg/mL of USP Levothyroxine RS in Solution A

Liothyronine stock solution: 0.4 mg/mL of USP Liothyronine RS in Solution A. Make a 1:100 dilution of this solution using Mobile phase.

Standard solution: 10 μg/mL of levothyroxine from Levothyroxine stock solution and 0.2 μg/mL of liothyronine from Liothyronine stock solution, in Mobile phase

Sample solution: Transfer an equivalent to about 100 μg of levothyroxine sodium, from finely powdered Tablets (NLT 20), to a centrifuge tube, add two glass beads, pipet 10 mL of Mobile phase into the tube, and mix on a vortex mixer for 3 min. Centrifuge to obtain a clear supernatant, filtering if necessary.

Sample solution 2 (for Tablets labeled to meet the requirements of Dissolution Test 3): Place the appropriate number of Tablets (see Table 1) into a suitable container, add 100.0 mL of Diluent, and shake by mechanical means for at least 30 min, or until the Tablets are fully disintegrated. Pass through a PTFE filter of 0.45-μm pore size.

Table 1

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.6-mm × 25-cm; packing L10

Flow rate: 1.5 mL/min

Injection volume: 100 μL

System suitability

Sample: Standard solution

Suitability requirements

Resolution: NLT 5.0 between liothyronine and levothyroxine

Relative standard deviation: NMT 2.0% for the levothyroxine peak

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) in the portion of Tablets taken:

Result = (r_U/r_S) × (C_S/C_U) × (M_r1/M_r2) × 100

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S  = concentration of USP Levothyroxine RS in the Standard solution (μg/mL)

C_U = nominal concentration of levothyroxine sodium in the Sample solution (μg/mL)

M_r1 = molecular weight of levothyroxine sodium, 798.85

M_r2 = molecular weight of levothyroxine, 776.87

Acceptance criteria: 95.0%–105.0%

4 PERFORMANCE TESTS

Change to read:

Dissolution 〈711〉

[Note—All containers that are in contact with solutions containing levothyroxine sodium are to be made of glass.]

Test 1

Medium: 0.01 N hydrochloric acid containing 0.2% sodium lauryl sulfate; 500 mL

Apparatus 2: 50 rpm

Time: 45 min

Mobile phase: Methanol and 0.1% phosphoric acid (6:4)

Standard stock solution: 0.1 mg/mL of USP Levothyroxine RS in methanol

Standard solution: Dilute the Standard stock solution with Medium to obtain a solution having a concentration similar to that expected in the Sample solution.

Sample solution: Pass a portion of the solution under test through a suitable filter. [Note—Before use, check the filters for absorptive loss of drug.]

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.6-mm × 25-cm; packing L1

Flow rate: 2 mL/min

Injection volume: 800 μL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 4.0% for levothyroxine

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) dissolved.

Tolerances: NLT 70% (Q) of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) is dissolved.

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

Medium, Apparatus 2, Mobile phase, Standard solution, Sample solution, Chromatographic system, and System suitability: Proceed as

directed for Test 1.

Time: 15 min

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) dissolved.

Tolerances: NLT 80% (Q) of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) is dissolved.

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

Medium, Apparatus 2, Time, Standard solution, and Sample solution: Proceed as directed for Test 1. [Note—Filter the Standard solution in a manner identical to that used for the Sample solution.]

Mobile phase: Acetonitrile and water (35:65) that contains 0.5 mL of phosphoric acid per liter of mixture

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.6-mm × 25-cm; 5-μm packing L10

Column temperature: 30°

Flow rate: 1.5 mL/min

Injection volume: 100 μL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 4.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) dissolved.

Tolerances: NLT 80% (Q) of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) is dissolved.

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

[Note—Do not use paddle stirrers with synthetic coating.]

Medium: 0.01 N hydrochloric acid; 500 mL for Tablets labeled to contain between 25 and 175 μg of levothyroxine sodium; and 900 mL for Tablets labeled to contain 200 or 300 μg of levothyroxine sodium

Apparatus 2: 75 rpm

Time: 45 min

Mobile phase: Acetonitrile, water, and phosphoric acid (500:700:2)

Standard stock solution: Transfer about 100 mg of USP Levothyroxine RS to a 100-mL volumetric flask. Add 80 mL of alcohol and 1 mL of 1N hydrochloric acid, sonicate for 2 min, dilute with alcohol to volume, and mix.

Standard solution: Dilute the Standard stock solution with a mixture of alcohol and water (1:1) to obtain a concentration of 0.01 mg/mL of levothyroxine. Dilute the resulting solution with Medium to obtain a final concentration similar to that expected in the Sample solution.

Sample solution: Sample per Dissolution 〈711〉. Centrifuge the solution under analysis.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.0-mm × 12.5-cm; packing L7

Flow rate: 1.5 mL/min

Injection volume: 500 μL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 4.0% of levothyroxine

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) dissolved.

Tolerances: NLT 80% (Q) of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) is dissolved.

Test 5: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 5.

Medium: 0.01 N hydrochloric acid containing 0.2% sodium lauryl sulfate; 500 mL

Apparatus 2: 50 rpm

Time: 30 min

Mobile phase: Acetonitrile, water, and phosphoric acid (32: 68: 0.05)

Standard stock solution: Transfer about 25 mg of USP Levothyroxine RS to a 250-mL volumetric flask. Add 50 mL of methanol, sonicate to dissolve, and dilute with methanol to volume.

Standard solution: 0.0004 mg/mL of USP Levothyroxine RS from Standard stock solution in Medium

Sample solution: Collect the sample using a suitable glass syringe and cannula.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.6-mm × 7.5-cm; 5-μm packing L10

Temperatures

Autosampler: 10°

Column: 30°

Flow rate: 1 mL/min

Injection volume: 80 μL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 4.0% for levothyroxine

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) dissolved.

Result = (r_U/r_S) × C_S × V × (M_r1/M_r2) × (1/L) × 100

r_U = peak response of levothyroxine from the Sample solution

r_S = peak response of levothyroxine from the Standard solution

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

V = volume of Medium, 500 mL

M_r1 = molecular weight of levothyroxine sodium, 798.85

M_r2 = molecular weight of levothyroxine, 776.87

L = label claim (mg/Tablet)

Tolerances: NLT 80% (Q) of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) is dissolved.

Test 7: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 7.

Medium: 0.01 N hydrochloric acid containing 0.2% sodium lauryl sulfate; 500 mL

Apparatus 2: 75 rpm

Time: 15 min

Solution A: 0.1% (v/v) phosphoric acid in water

Mobile phase: Methanol and Solution A (63:37)

Sample solution: Pass a portion of the solution under test through a suitable filter, discarding the first few milliliters.

Standard stock solution: 0.1 mg/mL of USP Levothyroxine RS in methanol. Sonicate as needed to dissolve.

Standard solution: USP Levothyroxine RS in Medium, from the Standard stock solution at a concentration similar to that of the Sample solution

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.6-mm × 25-cm; 10-μm packing L1

Temperatures

Autosampler: 12°

Column: 25°

Flow rate: 2 mL/min

Injection volume: 800 μL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 4.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) dissolved:

Result = (r_U/r_S) × C_S × V × (M_r1/M_r2) × (1/L) × 100

r_U = peak response of levothyroxine from the Sample solution

r_S = peak response of levothyroxine from the Standard solution

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

V = volume of Medium, 500 mL

M_r1 = molecular weight of levothyroxine sodium, 798.85

M_r2 = molecular weight of levothyroxine, 776.87

L = label claim (mg/Tablet)

Tolerances: NLT 80% (Q) of the labeled amount of levothyroxine sodium (C₁₅H₁₀I₄NNaO₄) is dissolved. (RB 1-Jun-2022)

Uniformity of Dosage Units 〈905〉: Meet the requirements

5 IMPURITIES

Limit of Liothyronine Sodium

[Note—Use Sample solution 2 for Tablets labeled to meet the requirements of Dissolution Test 3. For all other products, use the Sample solution.]

Mobile phase, Liothyronine stock solution, Standard solution, Sample solution, Chromatographic system, and System suitability: Proceed as directed in the Assay.

Liothyronine standard solution: 0.2 μg/mL of liothyronine from Liothyronine stock solution, in Mobile phase

Analysis

Samples: Sample solution and Liothyronine standard solution

Calculate the percentage of liothyronine sodium (C₁₅H₁₀I₄NNaO₄) in the portion of Tablets taken:

Result = (r_U/r_S) × (C_S/C_U) × (M_r1/M_r2) × 100

r_U = peak response of liothyronine from the Sample solution

r_S = peak response of liothyronine from the Liothyronine standard solution

C_S = concentration of USP Liothyronine RS in the Liothyronine standard solution (μg/mL)

C_U = nominal concentration of levothyroxine sodium in the Sample solution (μg/mL)

M_r1 = molecular weight of liothyronine sodium, 672.96

M_r2 = molecular weight of liothyronine, 650.98

Acceptance criteria: NMT 2.0% of liothyronine sodium

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers.

Labeling: When more than one Dissolution test is given, the labeling states the Dissolution test used only if Test 1 is not used.

USP Reference Standards 〈11〉

USP Levothyroxine RS

USP Liothyronine RS