Methyldopa Oral Suspension
» Methyldopa Oral Suspension is an aqueous suspension of Methyldopa. It contains one or more suitable flavors, wetting agents, and preservatives, and it may contain Sucrose. It contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of C10H13NO4.
Packaging and storage— Preserve in tight, light-resistant containers, and store at a temperature not exceeding 26.
USP Reference standards 11
USP Methyldopa RS Click to View Structure
Identification— Apply 10-µL portions of the Assay preparation and the Standard preparation prepared as directed in the Assay to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow to dry, develop the chromatogram in a solvent system consisting of equal volumes of acetone, butyl alcohol, glacial acetic acid, toluene, and water until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Locate the spots by staining the plate with iodine vapor for about 50 minutes, then view the plate under short-wavelength UV light: the RF value of the principal spot obtained from the Assay preparation corresponds to that obtained from the Standard preparation.
Uniformity of dosage units 905
for oral suspension packaged in single-unit containers: meets the requirements.
Deliverable volume 698
for oral suspension packaged in multiple-unit containers: meets the requirements.
pH 791: between 3.0 and 5.0; between 3.2 and 3.8 if sucrose is present.
Mobile phase— To 6.8 g of monobasic potassium phosphate add 750 mL of water, and stir until solution is complete. Adjust with 1 M phosphoric acid to a pH of 3.5, dilute with water to 1000 mL, mix, and pass through a filter having a 10-µm or finer porosity.
Standard preparation— Dissolve an accurately weighed quantity of USP Methyldopa RS in 0.1 N sulfuric acid to obtain a solution having a known concentration of about 1 mg of anhydrous methyldopa per mL.
Assay preparation— Transfer an accurately measured volume of Oral Suspension, freshly mixed, equivalent to about 250 mg of methyldopa, to a 250-mL volumetric flask, dilute with 0.1 N sulfuric acid to volume, and mix to dissolve the methyldopa. Pass the solution through a 0.45-µm membrane filter before using.
Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-mm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph three replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 2.0%.
Procedure— Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph by means of a suitable microsyringe or sampling valve, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C10H13NO4 in each mL of the Oral Suspension taken by the formula:
250(C/V)(rU / rS)
in which C is the concentration, in mg per mL, of USP Methyldopa RS in the Standard preparation; V is the volume, in mL, of Oral Suspension taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.
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Monograph Sujatha Ramakrishna, Ph.D.
Senior Scientific Liaison
(SM22010) Monographs - Small Molecules 2
Reference Standards RS Technical Services
USP35–NF30 Page 3871
Pharmacopeial Forum: Volume No. 32(2) Page 354