Metolazone Oral Suspension
» Metolazone Oral Suspension contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of metolazone (C16H16ClN3O3S). Prepare Metolazone Oral Suspension 1 mg per mL as follows (see Pharmaceutical Compounding—Nonsterile Preparations 795):
Metolazone 100 mg
Vehicle: a mixture of Vehicle for Oral Solution, (regular or sugar-free), NF and Vehicle for Oral Suspension, NF (1:1),  
a sufficient quantity to make 100 mL
If using Tablets, place the Metolazone Tablets in a suitable mortar, and comminute to a fine powder, or add Metolazone powder to the mortar. Add about 20 mL of the Vehicle, and mix to a uniform paste. Add the Vehicle in small portions, and transfer the contents of the mortar, stepwise and quantitatively, to a calibrated bottle. Add sufficient Vehicle in portions to rinse the mortar, add sufficient Vehicle to final volume, and mix well.
Packaging and storage— Preserve in tight, light-resistant containers. Store at controlled room temperature, or in a cold place.
Labeling— Label it to state that it is to be well shaken, and to state the beyond-use date.
USP Reference standards 11
USP Metolazone RS Click to View Structure
pH 791: between 3.6 and 4.6.
Beyond-use date: 60 days after the day on which it was compounded.
Mobile phase— Prepare a suitable filtered and degassed mixture of 700 mL of methanol, 300 mL of water, 1.5 g ammonium acetate, and 1 mL of diisopropylamine. Make adjustments if necessary (see System Suitability under Chromatography 621).
Standard preparation— Dissolve USP Metolazone RS in water to obtain a solution having a known concentration of 1.0 µg per mL.
Assay preparation— Agitate the container of Oral Suspension for 30 minutes on a rotating mixer, remove a 5-mL sample, and store in a clear glass vial at –70 until analyzed. At the time of analysis, remove the sample from the freezer, allow it to reach room temperature, and mix with a vortex mixer for 30 seconds. Pipet 1.0 mL of the sample into a 1000-mL volumetric flask, and dilute with Mobile phase to volume.
Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 20-cm analytical column that contains 5-µm packing L3. The flow rate is about 1.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the retention time for metolazone is about 6.0 minutes, and the relative standard deviation for replicate injections is not more than 2.2%.
Procedure— Separately inject equal volumes (about 20 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 quantity, in mg, of metolazone (C16H16ClN3O3S) in the volume of Oral Suspension taken by the formula:
1000(C/V)(rU / rS)
in which C is the concentration, in µg per mL, of USP Metolazone 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.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Jeanne H. Sun
Assistant Scientific Liaison
(CMP2010) Compounding
Reference Standards RS Technical Services
USP35–NF30 Page 3896
Pharmacopeial Forum: Volume No. 32(1) Page 119