Levothyroxine Sodium Tablets
DEFINITION
Levothyroxine Sodium Tablets contain NLT 95.0% and NMT 105.0% of the labeled amount of levothyroxine sodium (C15H10I4NNaO4).
IDENTIFICATION
•  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.
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:  Mixture of acetonitrile and water (4:6) containing 0.5 mL of phosphoric acid in each L of the mixture
Solution A:  Dissolve 400 mg of sodium hydroxide in 500 mL of water. Cool, and add 500 mL of methanol.
Diluent:  Mixture of methanol and water (6:4), containing 0.5 mL of phosphoric acid in each L of the 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:  Weigh and finely powder NLT 20 Tablets. Transfer a portion of the powder, equivalent to about 100 µg of levothyroxine sodium, to a centrifuge tube, add 2 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 below) 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
Tablet Strength
(µg/Tablet of Levothyroxine Sodium)
Number of Tablets
Less than 100 20
At least 100 but less than 200 15
200 or more 10
Chromatographic system  
Mode:  LC
Detector:  UV 225 nm
Column:  4.6-mm × 25-cm; packing L10
Flow rate:  1.5 mL/min
Injection size:  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 C15H10I4NNaO4 in the portion of Tablets taken:
Result = (rU/rS) × (CS/CU) × (Mr1/Mr2) × 100
rU== peak response from the Sample solution
rS== peak response from the Standard solution
CS== concentration of USP Levothyroxine RS in the Standard solution (µg/mL)
CU== nominal concentration of levothyroxine sodium in the Sample solution (µg/mL)
Mr1== molecular weight of levothyroxine sodium, 798.85
Mr2== molecular weight of levothyroxine, 776.87
Acceptance criteria:  95.0%–105.0%
PERFORMANCE TESTS
•  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
Determine the amount of C15H10I4NNaO4 dissolved by using the following method.
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  
Mode:  LC
Detector:  UV 225 nm
Column:  4.6-mm × 25-cm; packing L1
Flow rate:  2 mL/min
Injection size:  800 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 amount of C15H10I4NNaO4 dissolved.
Tolerances:  NLT 70% (Q) of the labeled amount of C15H10I4NNaO4 is dissolved.
Test 2:  If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 2.
Medium, Apparatus, 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 amount of C15H10I4NNaO4 dissolved.
Tolerances:  NLT 80% (Q) of the labeled amount of C15H10I4NNaO4 is dissolved.
Test 3:  If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 3.
Medium, Apparatus, Time, Standard solution, and Sample solution:  Proceed as directed in Test 1. [Note—Filter the Standard solution in a manner identical to the Sample solution. ]
Determine the amount of C15H10I4NNaO4 dissolved by employing the following method.
Mobile phase:  Acetonitrile and water (35:65) that contains 0.5 mL/L of phosphoric acid
Chromatographic system 
Mode:  LC
Detector:  UV 225 nm
Column:  4.6-mm × 25-cm; 5-µm packing L10
Temperature:  30
Flow rate:  1.5 mL/min
Injection size:  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 amount of C15H10I4NNaO4 dissolved.
Tolerances:  NLT 80% (Q) of the labeled amount of 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
Determine the amount of C15H10I4NNaO4 dissolved by using the following method.
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 1 N 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 solution having 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  
Mode:  LC
Detector:  UV 225 nm
Column:  4.0-mm × 12.5-cm; packing L7
Flow rate:  1.5 mL/min
Injection size:  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 amount of C15H10I4NNaO4 dissolved.
Tolerances:  NLT 80% (Q) of the labeled amount of C15H10I4NNaO4 is dissolved.
•  Uniformity of Dosage Units 905: Meet the requirements
IMPURITIES
Organic Impurities 
•  Procedure: 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, Standard solution, Sample solution, Chromatographic system, and System suitability:  Proceed as directed in the Assay.
Analysis:  Calculate the percentage of C15H11I3NNaO4 in the portion of Tablets taken:
Result = (rU/rS) × (CS/CU) × (Mr1/Mr2) × 100
rU== peak response of liothyronine from the Sample solution
rS== peak response of liothyronine from the Standard solution
CS== concentration of USP Liothyronine RS in the Standard solution (µg/mL)
CU== nominal concentration of levothyroxine sodium in the Sample solution (µg/mL)
Mr1== molecular weight of liothyronine sodium, 672.96
Mr2== molecular weight of liothyronine, 650.98
Acceptance criteria:  NMT 2.0% of liothyronine
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 Click to View Structure
USP Liothyronine RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Principal Scientific Liaison
1-301-816-8251
(SM32010) Monographs - Small Molecules 3
711 Margareth R.C. Marques, Ph.D.
Senior Scientific Liaison
1-301-816-8106
(GCDF2010) General Chapters - Dosage Forms
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 3679
Pharmacopeial Forum: Volume No. 34(4) Page 954