Liothyronine Sodium

(lye'' oh thye' roe neen soe' dee um).

C15H11I3NNaO4

672.96

l-Tyrosine, O-(4-hydroxy-3-iodophenyl)-3,5-diiodo-, monosodium salt.
Monosodium l-3-[4-(4-hydroxy-3-iodophenoxy)-3,5-diiodophenyl]alanine

[55-06-1].

» Liothyronine Sodium is the sodium salt of l-3,3¢,5-triiodothyronine. It contains not less than 95.0 percent and not more than 101.0 percent of C15H11I3NNaO4, calculated on the dried basis.

Packaging and storage— Preserve in tight containers.

USP Reference standards

—

USP Levothyroxine RS

USP Liothyronine RS

Identification—

A: The UV absorption spectrum of a 1 in 10,000 solution in dilute hydrochloric acid (1 in 50) in 80 percent alcohol exhibits maxima at the same wavelengths as that of a similar solution of USP Liothyronine RS, concomitantly measured; and the respective absorptivities, both calculated on the dried basis in terms of the acid, at the wavelength of maximum absorbance at about 297 nm, do not differ by more than 5.0%.

B: Heat about 50 mg with a few drops of sulfuric acid in a porcelain crucible: violet vapors of iodine are evolved.

C: The residue from the ignition of it meets the requirements of the tests for Sodium

191

D: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Specific rotation

781S

: between +18

and +22

Test solution: 20 mg per mL, in a mixture of alcohol and 1.2 N hydrochloric acid (4:1).

Loss on drying

731

— Dry it at 105

for 2 hours: it loses not more than 4.0% of its weight.

Limit of levothyroxine sodium—

Mobile phase and Chromatographic system— Proceed as directed in the Assay.

Standard solution— Proceed as directed for Standard preparation in the Assay.

Test solution— Proceed as directed for Assay preparation in the Assay.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the levothyroxine peak responses. Calculate the percentage of levothyroxine sodium (C15H10I4NNaO4) in the portion of Liothyronine Sodium taken by the formula:

100(798.85/776.87)(CS / CT)(rU / rS)

in which 798.85 and 776.87 are the molecular weights of levothyroxine sodium and levothyroxine, respectively; CS is the concentration, in µg per mL, of USP Levothyroxine RS in the Standard solution; CT is the concentration, in µg per mL, of Liothyronine Sodium in the Assay preparation; and rU and rS are the levothyroxine peak responses obtained from the Test solution and the Standard solution, respectively: not more than 5.0% of levothyroxine sodium is found.

Chloride content— Weigh accurately 100 mg, previously dried, and transfer to a platinum dish. Ignite over a low flame, protecting the dish from air currents during the ignition. When carbonization is complete, cool the dish, add 2 drops of water, and break up the charred mass thoroughly with a stirring rod. Add 10 mL of water and 5 mL of ammonium hydroxide, and mix. Transfer the slurry to a glass-stoppered, 50-mL flask, and wash the platinum dish and the stirring rod with water, adding the washings to the flask, until the volume of the solution is about 25 mL. Add 10 mL of silver nitrate solution (1 in 20), shake thoroughly, and filter through a retentive paper into a 50-mL color-comparison tube. Wash the flask and the filter paper with 10 mL of water, and add the washings to the tube. Acidify the combined filtrate and washings to litmus with nitric acid, and dilute with water to 50 mL. Prepare a control by mixing 5 mL of ammonium hydroxide, 20 mL of water, and 10 mL of silver nitrate solution (1 in 20), filtering the mixture through a retentive paper into a 50-mL color-comparison tube, then washing the filter paper with 10 mL of water into the tube, acidifying the contents of the tube to litmus with nitric acid, diluting with water to 50 mL, and adding sodium chloride solution (1 in 1000) in 0.1-mL increments until the turbidity of the control matches that of the test solution. Not more than 2.0 mL of sodium chloride is required (1.2%).

Sodium content— Weigh accurately about 100 mg, previously dried, and transfer to a platinum dish. Add 8 to 10 drops of sulfuric acid, and ignite to constant weight, taking care to avoid spattering. Each mg of residue is equivalent to 0.324 mg of Na. Correct the result for the amount of sodium equivalent to the NaCl found in the test for Chloride content: not less than 2.9% and not more than 4.0% is found.

Assay—

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (60:40) that contains 0.5 mL of phosphoric acid in each 1000 mL. Make adjustments if necessary (see System Suitability under Chromatography

621

0.01 M Methanolic sodium hydroxide— Dissolve 400 mg of sodium hydroxide in 500 mL of water. Cool, add 500 mL of methanol, and mix.

Liothyronine stock solution— Dissolve an accurately weighed quantity of USP Liothyronine RS in 0.01 M Methanolic sodium hydroxide to obtain a solution having a known concentration of about 0.4 mg of liothyronine per mL.

Levothyroxine stock solution— Dissolve an accurately weighed quantity of USP Levothyroxine RS in 0.01 M Methanolic sodium hydroxide to obtain a solution having a known concentration of about 0.4 mg of levothyroxine per mL. Make a 1:100 dilution of this solution using Mobile phase.

Standard preparation— Transfer appropriate volumes of Liothyronine stock solution and Levothyroxine stock solution to a suitable container, and dilute quantitatively and stepwise, if necessary, with Mobile phase to obtain a solution having known concentrations of about 10 µg of liothyronine per mL and 0.5 µg of levothyroxine per mL.

Assay preparation— Prepare a solution of Liothyronine Sodium in Mobile phase having a known concentration of about 10 µg per mL. [note—A small amount of 0.01 M Methanolic sodium hydroxide can be used to facilitate the dissolution of the sample. ]

Chromatographic system (see Chromatography

621

)— The liquid chromatograph is equipped with a 225-nm detector and a 4.6-mm × 25-cm column that contains packing L10. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between levothyroxine and liothyronine is not less than 5.0; and the relative standard deviation for replicate injections is not more than 2.0% for liothyronine.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of C15H11I3NNaO4 in the portion of Liothyronine Sodium taken by the formula:

100(672.96/650.97)(CS / CT)(rU / rS)

in which 672.96 and 650.97 are the molecular weights of liothyronine sodium and liothyronine, respectively; CS is the concentration, in µg per mL, of USP Liothyronine RS in the Standard preparation; CT is the concentration, in µg per mL, of Liothyronine Sodium in the Assay preparation; and rU and rS are the liothyronine peak responses obtained from the Assay preparation and the Standard preparation, respectively.

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
Reference Standards	RS Technical Services 1-301-816-8129 rstech@usp.org

USP35–NF30 Page 3692

Pharmacopeial Forum: Volume No. 33(3) Page 426