Levocarnitine 

C₇H₁₅NO₃                                                                                          Mol. Wt. 161.20   

Levocarnitine is (R)-3-Carboxy-2-hydroxy-N,N,N-trimethyl-1-propanaminium, inner salt; (R)-(3-Carboxy-2-hydroxypropyl) trimethylammonium, inner salt.

Levocarnitine contains not less than 97.0 per cent and not more than 103.0 per cent of C₇H₁₅NO₃, calculated on the anhydrous basis.

Category.  Kidney disease on dialysis.

Dose. 990 mg 1 to 3 times a day, depending on clinical response.

Description. A white crystals or crystalline powder; hygroscopic.

Identification

Dry the sample and reference standard under vacuum at 50⁰ for 5 hours and determine by infrared absorption spectrophotometry (2.4.6). Compare the spectrum with that obtained with levocarnitine RS or with the reference spectrum of levocarnitine. 

Tests

Specific optical rotation (2.4.22).  – 0.29º to – 0.32º, determined in a 10.0 per cent w/v solution in carbon dioxide-free water.

pH (2.4.24). 5.5 to 9.5, determined in a 5.0 per cent w/v solution in carbon dioxide-free water.

Chloride. Not more than 4000 ppm.

Test solution.  Dissolve 0.09 g of levocarnitine in 30 to 40 ml of water, neutralise the solution with nitric acid,  to litmus. Add 1 ml of nitric acid and 1 ml of silver nitrate solution, make up the volume to 50.0 ml with water.

Reference solution.  Mix 0.5 ml of 0.02 M hydrochloric acid in 30 to 40 ml of water, neutralise the solution with nitric acid, to litmus. Add 1 ml of nitric acid and 1 ml of silver nitrate solution, make up the volume to 50.0 ml with water.

Allow to stand for 5 minutes protected from direct sunlight. Compare the turbidity of test solution, if any, with that produced with reference solution.  

 

Potassium. Not more than 0.2 per cent.

Determine by atomic absorption spectrophotometry (2.4.2),

Note— The reference solution and the test solutions may be modified, if necessary, to obtain solutions of suitable concentrations adaptable to the linear or working range of the instrument.

Reference solution.  A 0.003125 per cent w/v solution of potassium in water. The solution prepared from potassium chloride, previously dried at 105° for 2 hours.

Test solution (a).  A 0.0625 per cent w/v solution of the substance under examination in water.

Test solution (b).  Transfer 20.0 ml of the test solution (a) to a 25-ml volumetric flask, and dilute with water to volume, without reference solution.

Test solution (c).  Transfer 20.0 ml of the test solution (a) to a 25-ml volumetric flask, add 2.0 ml of the reference solution, and dilute with water to volume.

Test solution (d).  Transfer 20.0 ml of the test solution (a) to a 25-ml volumetric flask, add 4.0 ml of the reference solution, and  dilute with water to volume.

Blank. Water

 

Instrumental conditions 

-spectrophotometer set at 766.7 nm,

-lamp:  potassium hollow-cathode,

-flame:  Air–acetylene.  

Measure the absorbances of the test solution (b), test solution (c) and test solution (d) against blank solution. Plot the absorbances of the three test solutions versus their added potassium concentrations, in µg/ml. Draw the straight line best fitting the three points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the concentration, in µg/ml, of potassium in test solution (b).

Calculate the percentage of potassium in the portion of levocarnitine taken:

Result = ( C_K / C_U ) × 100

CK	=	concentration of potassium in test solution A (µg/ml), determined from the intercept of the linear regression line
CU	=	concentration of levocarnitine in test solution A (µg/ml)

 

Sodium. Not more than 0.1 per cent.

Determined by atomic absorption spectrophotometry (2.4.2),

Note— The reference solution and the test solutions may be modified, if necessary, to obtain solutions of suitable concentrations adaptable to the linear or working range of the instrument.

Reference solution.  A 0.025 per cent w/v solution  of sodium in water, the solution prepared from sodium chloride, previously dried at 105° for 2 h.

Test solution(a).  A 4.0 per cent w/v solution of the substance under examination in water.

Test solution(b).  Transfer 20.0 ml of the test solution (a) to a 25-ml volumetric flask, and dilute with water to volume without reference solution.

Test solution(c).  Transfer 20.0 ml of the test solution (a) to a 25-ml volumetric flask, add 2.0 ml of the reference solution, and dilute with water to volume.

Test solution(d).  Transfer 20.0 ml of the test solution (a) to a 25-ml volumetric flask, add 4.0 ml of the reference solution, and dilute with water to volume.

Blank.  Water

 

Instrumental conditions 

-spectrophotometer set at 589 nm,

-lamp:  sodium hollow-cathode,

-flame:  Air–acetylene. 

Measure the absorbances of the test solution (b), test solution (c) and test solution (d) against blank solution. Plot the absorbances of the three test solutions versus their added potassium concentrations, in µg/ml. Draw the straight line best fitting the three points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the concentration, in µg/ml, of sodium in test solution (b).

Calculate the percentage of sodium in the portion of levocarnitine taken:

Result = ( C_Na / C_U ) × 100

CNa	=	concentration of sodium in test solution A (µg/ml), determined from the intercept of the linear regression line
CU	=	concentration of levocarnitine in test solution A (µg/ml)

Heavy metals (2.3.13). 1.0 g complies with the limit test for heavy metals, Method A (20 ppm).

Water (2.3.43). Not more than 4.0  per cent.

Sulphated ash (2.3.18). Not more than 0.5 per cent.

Assay. Dissolve 0.1 g in a mixture of 3 ml of formic acid and 50.0 ml of glacial acetic acid. Titrate with 0.1 M perchloric acid, using crystal violet solution as indicator. Carry out a blank titration.

1 ml of 0.1 M perchloric acid is equivalent to 0.01612 g of C7H15NO₃.

Storage. Store in tight containers.

Solubility. Freely soluble in water and in hot alcohol;  practically insoluble in acetone; in ether; and in benzene.