STABILIZED LIQUID FORMULATION OF LEVOTHYROXINE

Background of the Invention

Thyroxine active drugs are known for both therapeutic and prophylactic treatment of thyroid disorders. The thyroid accomplishes its regulation functions by producing the hormones L-triiodothyronine (liothyronine; T3) and L-thyroxine (levothyroxine; T4). The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.

Administration of levothyroxine sodium provides T4 to a patiënt. Once absorbed, the administered T4 behaves identically to T4 that otherwise would be secreted by the thyroid gland of the patiënt, and binds to the same serum proteins, providing a supply of circulating T4-thyroglobulin in the patiënt. The administered T4 may be deiodinated in vivo to T3. As a result, a patiënt receiving appropriate doses of levothyroxine sodium will exhibit normal blood levels of T3, even when the patient's thyroid gland has been removed or is not functioning.

Levothyroxine sodium is prescribed for thyroid hormone replacement therapy in cases of reduced or absent, thyroid function e.g., ailments such as myxedema, cretinism and obesity. Levothyroxine sodium is quite unstable, hygroscopic and degrades rapidly when subjected to high humidity, light or high temperature. Because of the physicochemical properties of the drug, formulations of levothyroxine sodium have extremely short stability duration, worsened under conditions of high humidity and temperature.

Levothyroxine sodium is available in the form of capsules, tablets and parenteral dosage forms. Levothyroxine sodium for injection is available as sterile lyophilized product for parenteral administration containing 100 mcg/vial, 200 mcg/vial and 500 mcg/vial.

Conventional formulations of levothyroxine sodium for injection are preservative-free lyophilized powders containing synthetic crystalüne levothyroxine sodium, mannitol, tribasic sodium phosphate, and sodium hydroxide. These' conventional formulations typically contain mannitol, tribasic sodium phosphate and levothyroxine sodium. Administration of the conventional formulation involves reconstitution of the lyophilized powder .in 5mL of 0.9% sodium chloride injection, to provide injectable solutions having levothyroxine sodium concentrations of 20mcg/mL, 40mcg/mL or lOOmcg/mL.'
U.S Pat. No. 9,006,289, issued on April 14, 2015, to Jiang, et al., discloses lyophilized composition comprising of levothyroxine sodium, a phosphate buffer and mannitol.

Levothyroxine has extrernely short stability, worsened under conditions of high humidity and temperature. Due to this instability, Levothyroxine injectable formulations are used in the form of lyophilized formulations that are dissolved in 0.9% sodium chloride Injection immediately before injection. The present inventors have developed stable liquid formulations of Levothyroxine intended for parenteral administration.

Summary of the Invention

One object of the invention pro vides stable liquid parenteral pharmaceutical formulation of Levothyroxine.

Another aspect of the invention provides stable liquid parenteral pharmaceutical formulation of Levothyroxine comprising Levothyroxine, stabilizing agents, one or more solvents and other pharmaceutically acceptable excipients thereof.

Yet another aspect of the invention provides liquid parenteral pharmaceutical formulation of Levothyroxine comprising Levothyroxine sodium, stabilizing agents, buffering agents, one or more solvents and other pharmaceutically acceptable excipients thereof.

Detailed description of the Invention
The present invention relates to stable liquid parenteral formulation of Levothyroxine, and more particularly to stable Levothyroxine liquid formulation comprising of buffering agents, stabilizing agents, solvents and other pharmaceutically acceptable excipients thereof.

In the context of this invention "Levothyroxine" refers to the pharmaceutically acceptable salts, solvates, hydrates and anhydrous forms thereof. The formulations of the present invention preferably comprise Levothyroxine sodium.
As used herein, "liquid parenteral formulations of Levothyroxine" refers to formulations that contain Levothyroxine in dissolved or solubilised form and are intended to be used as such or upon dilution in intravenous diluents.

Levothyroxine sodium is quite unstable, hygroscopic and degrades rapidly when subjected to high humidity, light or high temperature. Degradation is further enhanced by the presence of water. Hence, attempts to develop an intravetious preparation of Levothyroxine were limited.

The inventors of the present invention have surprisingly found that it is possible to develop stable liquid parenteral pharmaceutical formulation of Levothyroxine, despite its rapid degrading nature.

One embodiment of the invention relates to liquid parenteral pharmaceutical formulations of Levothyroxine comprising:
i. Levothyroxine
ii. stabilizing agents
iii. one or more solvents and other pharmaceutically acceptable excipients thereof.

Yet another embodiment of the invention relates to liquid parenteral pharmaceutical formulation of Levothyroxine comprising:
i. Levothyroxine sodium
ii. stabilizing agents
iii. buffering agents
iv. one or more solvents and
v. optionally one or more pharmaceutically acceptable excipients selected from solubilizing agents, pH adjusting agents, anti-oxidants and preservatives.

Stabilizing agents used in the formulation include, but not limited to sodium iodide, potassium iodide and the like.
Suitable buffering agents include amino acids such as arginine, alanine, histidine, glycine and lysine and other buffers such as citrate, glutamate, bicarbonate, tartrate, benzoate, lactate, gluconate, TRIS, acetate, megluminë, borate and phosphate buffer.

Suitable solvents include, but not limited to dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, dimethylisosorbide, ethanol, propylene glycol, polyethylene alcohol, propylene glycol esters, polyethylene glycols, glycerine, water and the like. Preferred solvents are water and propylene glycol.

The phannaceutical compositions of the present invention may also contain solubilizing agents such as cyclodextrins. Cyclodextrins also act as stabilizing agents. These agents may be used in the formulation to maintain the solubility and stability of levothyroxine sodium during the entire shelf life of the formulation. Suitable cyclodextrins include but not limited to a, P and y-cyclodextrin and cyclodextrins modified with alkyl-, hydroxyalkyl-, dialkyl-, and sulfoalkyl-ether modified cyclodextrins such as methyl or hydroxypropyl (3-cyclodextrins (HPpCD), methyl-and-ethyl-P-cyclodextrin, sulfoalkylether-substituted beta-cyclodextrin, sulfobutylether-P-cyclodextrin (SBECD) and the like.

Suitable pH adjusting agents include sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, ammonium carbonate, hydrochloric acid, citric acid, lactic acid, phosphoric acid, sodium phosphate, sulfuric acid and the like.

The pharmaceutical compositions of the present invention may also contain one or more anti-oxidants such as sodium sulfite, sodium bisulfite, sodium metabisulfite, sodium thiosulphate, sodium formaldehyde sulfoxylate, citric acid, tocopherol, butylated hydroxy anisole, butylated hydroxy toluene, monothioglycerol, ascorbic acid, sodium ascorbate and propyl gallate.
The inventors carried out experiments with various buffering agents to determine suitable buffering agent in the final formulation. Levothyroxine formulations prepared were tested for stability at 60±2°C (3 days). The data is summarized in table 1.
Table 1: Evaluation of different buffering agents for their suitability in the formulation.
Ingrediënt Quantity in mg
Al A2 A3 A4 A5 A6
Levothyroxine sodium '0.05 0.05 0.05 0.05 0.05 0.5
Arginine 10 - - - - -
Sodium carbonate buffer - 10 - - - -
Sodium hydrogen . carbonate buffer - - 10 - - -
Tris buffer - - - 8 - -
Tri basic sodium phosphate dodeca hydrate buffer - - - 2.3 -
Meglumine buffer - - - - - 1
Mannitol 1.5 1.5 1.5 1.5 1.5 -
Sodium hydroxide q.s to adjust the pH 11.0±1.0
Water for Injection Qsto lml
Observations
60±2°C (3 days)
Total impurities 3.14 5.49 6.42 5.82 11.99 4.8

A preferred embodiment of the invention relates to liquid parenteral pharmaceutical formulation of Levothyroxine comprising: i. . Levothyroxine sodium ii. stabilizing agents iii. buffering agent(s) selected from aminoacids such as arginine, alanine, histidine,
glycine and lysine; other buffers include citrate, glutamate, bicarbonate; tartrate,
benzoate, lactate, gluconate, TRIS, acetate, borate and phosphate buffer iv. one or more solvents selected from the group comprising water, polyethylene
glycol, ethanol, propylene glycol and glycerine v. optionally one or more pharmaceutically acceptable excipients selected from
solubilizing agents, pH adjusting agents, anti-oxidants and preservatives.
Levothyroxine formulation prepared according to the invention was tested for stability at 2-8°C, 25°C and 60°C for a period of 1 month. The stability data of the invention formulation is summarized in table 2?
Table 2: Stability data of the product prepared according to example 5.
Levothyroxine sodium Invention formulation stability data
Storage condition 2-8°C 2-8°C 25°C 25°C 60°C 60°C
Storage duration 1 week 1 month 1 week 1 month 1 week 1 month
Total impurities 0.39 0.50 0.43 0.55 0.58 1.10 .
pH 6.25 6.40 6.67 6.81 6.21 6.47
Osmolality (mOsm/kg) 272 • 255 263 238 266 262
Surprisihgly no significant increase in impurities was observed even at accelerated conditions. The data confirms the inventors' finding that Levothyroxine formulations in the presence of suitable excipients in suitable proportions resulted in a stable product.
The following examples further describe certain specific aspects and embodiments of the present invention and demonstrate the practice and advantages thereof. It is to be

understood that the examples are given by way of illustration only and are not intended to limit the scope of the invention in any manner.
Example 1
Ingredients Quantity
Levothyroxine sodium 0.01-1 mg
Arginine 0.01-4 mg
Propylene glycol 0.01 - 1 ml
Sodium hydroxide qs
Water for injection QstoO.l -2ml
Manufacturing process
Water for injection was taken in a compounding vessel and arginine was added and stirred. Propylene glycol was added to the above solution and stirred. Then the bulk solution was cooled to 2°C to 8°C. Levothyroxine sodium was added and stirred till a clear solution was obtained, while maintaining the temperature at 5±3°C. pH of the solution was adjusted to 11 ± 1.0 by the addition of sodium hydroxide solution. The solution was filtered, followed by stoppering and sealing of the vials.
Example 2
Ingredients Quantity
Levothyroxine sodium O.OMmg
Alanine 0.006 - 4 mg
Propylene glycol 0.01 - 1 ml
Sodium hydroxide qs
Water for injection QstoO.l -2ml
Manufacturing process
Water for injection was taken in a compounding vessel and alanine was added and stirred. Propylene glycol was added to the above solution and stirred. Then the bulk solution was cooled to 2°C to 8°C. Levothyroxine sodium was added and stirred till a

clear solution was obtained, while maintaining the temperature at 5±3°C. The solution was filtered, followed by stoppering and sealing of the vials.
Example 3
S.No Ingredients Quantity
1. Levothyroxine sodium 0.01-1 mg
2. L-Arginine 250mcg
3, Sodium acetate anhydrous 10500 meg
4. . Potassium hydroxide 1500mcg
5. Sodium metabisulfite 500 meg
6. Sodium iodide lOOOmcg
7. Water for injection QstoO.l -6ml
Manufacturing process
L-Arginine was added to the manufacturing vessel containing water for injection, sodium acetate anhydrous was added to the above solution and stirred well. Potassium hydroxide was added to the above solution followed by the addition of sodium metabisulfite and sodium iodide. The solution was cooled to 2-8°C. Levothyroxine sodium was added to the above solution and stirred till a homogeneous solution was obtained.
Example 4
S.No Ingredients Quantity
1. Levothyroxine sodium 0.01-1 mg
2. Arginine 250mcg
3. Sodium acetate.anhydrous 10500 meg
4: Potassium hydroxide 1500mcg
5. Sodium iodide lOOOmcg
6. Water for injection QstoO.l -6ml

Manufacturing process
L-Arginine was added to the manufacturing vessel containing water for injection, sodium acetate anhydrous was added to the above solution and stirred well. Potassium hydroxide was added to the above solution followed by the addition of sodium iodide. The solution was cooled to 2-8°C. Levothyroxine sodium was added to the above solution and stirred till a homogeneous solution was obtained.
Example 5
S.No Ingredients Quantity
1. Levothyroxine sodium 0.01-1 mg
2. Arginine 0.05mg
Sulfobutylether-p-cyclodextrin(SBECD) 83.9mg
4. Sodium iodide 2.00mg
5. Water for injection QstoO.l -3ml
Brief Manufacturing Process
SBECD was added to the manufacturing vessel containing water for injection followed by the addition of Levothyroxine sodium. Arginine was added and stirred, well, till a clear solution was obtained. Sodium iodide was added to the above solution. The pH of the solution was adjusted to 6.0 ± 1.0 (if necessary) with sodium hydroxide/hydrochloric acid.

We claim

Claim 1: A stable liquid parenteral pharmaceutical formulation of Levothyroxine comprising Levothyroxine and other pharmaceutically acceptable excipients thereof.

Claim 2: A stable, liquid parenteral pharmaceutical formulation of Levothyroxine comprising
(i) Levothyroxine
(ii) stabilizing agent
(iii) one or more solvents and
(iv) one or more pharmaceutically acceptable excipients thereof.

Claim 3: A stable, liquid parenteral pharmaceutical formulation of claim 2, comprising (i) Levothyroxine sodium (ii) stabilizing agents (iii) buffering agents (iv) one or more solvents
(v) optionally one or more pharmaceutically acceptable excipients selected from solubilizing agents, pH adjusting agents and anti-oxidants.

Claim 4: A stable, liquid parenteral pharmaceutical formulation of claim 3, comprising (i) Levothyroxine sodium (ii) stabilizing agents (iii) buffering agent(s) selected from aminoacids such as arginine, alanine,histidine, glycine and lysine; citrate, glutamate, bicarbonate, tartrate,benzoate, lactate, gluconate, TRIS, acetate, meglumine, borate and phosphate buffer, (iv) one or more solvents selected from the group comprising water,polyethylene glycol, ethanol, propylene glycol and glycerine (v) optionally one or more pharmaceutically acceptable excipients selected from solubilizing agents, pH adjusting agents and anti-oxidants.

Claim 5: A stable, liquid parenteral pharmaceutical formulation of Levothyroxine comprising
(i) Levothyroxine sodium
(ii) stabilizing agent and/or solubilizing agent
(iii) buffering agent
(iv) one or more solvents selected from water, propylene glycol ethanol, polyethylene glycol and glycerine.

Claim 6: A stable, liquid parenteral pharmaceutical formulation of Levothyroxine comprising
(i) Levothyroxine sodium
(ii) sodium iodide
(iii) cyclodextrin
(iv) arginine
(v) one or more solvents selected from water, propylene glycol ethanol, polyethylene glycol and glycerine.

Claim 7: A stable, liquid, parenteral pharmaceutical formulation '"of claim 5, wherein solubilizing agent is selected from cyclodextrins.

Claim 8: A stable, liquid parenteral pharmaceutical formulation of claims 6 and 7, wherein the cyclodextrin is selected from a, (3 and y-cyclodextrin. and cyclodextrins modified with alkyl-, hydroxyalkyl-, dialkyl-, and sulfoalkyl-ether -modified cyclodextrins such as methyl or hydroxypropyl P-cyclodextrins (HPPCD), sulfoalkylether-substituted beta-cyclodextrin, sulfobutylether-p-cyclodextrin (SBECD).