Methylphenobarbital Tablets

General Notices

Action and use

Barbiturate.

Definition

Methylphenobarbital Tablets contain Methylphenobarbital.

The tablets comply with the requirements stated under Tablets and with the following requirements.

Content of methylphenobarbital, C13H14N2O3

95.0 to 105.0% of the stated amount.

Identification

A. Transfer a quantity of the finely powdered tablets containing 0.20 g of Methylphenobarbital to a long-stemmed, sintered glass filter (ISO 4793, porosity grade 3, is suitable), wash with 15 mL of petroleum ether (boiling range 40° to 60°), stir for 2 to 3 minutes and filter; repeat the extraction with two 15 mL quantities of petroleum ether (boiling range 40° to 60°). Discard the filtrates, extract the residues with two 15 mL quantities of dichloromethane, combine the extracts, evaporate to dryness on a water bath and dry the residue at 105° for 30 minutes to 1 hour. The infrared absorption spectrum of the dried residue, Appendix II A, is concordant with the reference spectrum of methylphenobarbital (RS 388).
B. In the Assay, the chromatogram obtained with solution (1) shows a peak with the same retention time as the principal peak in the chromatogram obtained with solution (2).

Tests

Dissolution

Comply with the requirements for Monographs of the British Pharmacopoeia in the dissolution test for tablets and capsules, Appendix XII B1, using Apparatus 2 and rotating the paddle at 75 revolutions per minute. Use as the medium 900 mL of a borate buffer of pH 10.0 prepared by dissolving 3.093 g of boric acid, 3.730 g of potassium chloride and 1.75 g of sodium hydroxide in 200 mL of water and diluting the solution to 1000 mL with water. Withdraw a sample of 20 mL of the medium and filter. Dilute the filtrate, if necessary, with the dissolution medium to give a solution expected to contain about 0.002% w/v of Methylphenobarbital. Measure the absorbance of this solution, Appendix II B, at the maximum at 242 nm using dissolution medium in the reference cell. Calculate the total content of methylphenobarbital, C13H14N2O3, in the medium from the absorbance obtained from a 0.0020% w/v solution of methylphenobarbital BPCRS in dissolution medium and using the declared content of C13H14N2O3 in methylphenobarbital BPCRS.

Related substances

Carry out the method for liquid chromatography, Appendix III D, using the following solutions. For solution (1) add 120 mL of methanol to a quantity of the powdered tablets containing 30 mg of Methylphenobarbital, mix with the aid of ultrasound for 10 minutes, add 50 mL of water, cool and dilute to 200 mL with methanol. For solution (2) dilute 1 volume of solution (1) to 100 volumes with methanol (75%).

The chromatographic procedure may be carried out using (a) a stainless steel column (15 cm × 4.6 mm) packed with particles of silica 5 µm in diameter the surface of which has been modified with chemically bonded hexyl groups (Spherisorb Hexyl is suitable) and maintained at 40°, (b) as the mobile phase with a flow rate of 2 mL per minute a mixture of 55 volumes of 0.045m disodium hydrogen orthophosphate adjusted to pH 6.5 with orthophosphoric acid and 45 volumes of methanol, adjusted to pH 6.0 with orthophosphoric acid and (c) a detection wavelength of 235 nm.

Inject 20 µL of each solution. In the chromatogram obtained with solution (1) the sum of the areas of any secondary peaks is not greater than the area of the principal peak in the chromatogram obtained with solution (2) (1%).

Assay

Carry out the method for liquid chromatography, Appendix III D, using the following solutions. For solution (1) add 120 mL of methanol to a quantity of the powdered tablets containing 30 mg of Methylphenobarbital, mix with the aid of ultrasound for 10 minutes, add 50 mL of water, cool and dilute to 200 mL with methanol. Prepare solution (2) in the same manner as solution (1) but using 30 mg of methylphenobarbital BPCRS in place of the powdered tablets.

The chromatographic procedure described under the test for Related substances may be used.

Inject 10 µL of each solution. Calculate the content of C13H14N2O3 using the declared content of C13H14N2O3 in methylphenobarbital BPCRS.