Lamotrigine Compounded Oral Suspension

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Lamotrigine Compounded Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled amount of lamotrigine (C₉H₇Cl₂N₅).

Prepare Lamotrigine Compounded Oral Suspension 1 mg/mL as follows (see Pharmaceutical Compounding—Nonsterile Preparations 〈795〉).

^a Lamotrigine 100-mg tablet, Torrent Pharmaceuticals LTD, Kalamazoo, MI.

^b Perrigo, Minneapolis, MN.

Place the required number of tablet(s) in a suitable mortar, and comminute to a fine powder. Add the Ora-Blend in small portions, and triturate to make a smooth paste. Add increasing volumes of the Ora-Blend to make a lamotrigine liquid that is pourable. Transfer the contents of the mortar, stepwise and quantitatively, to a calibrated bottle. Add enough of the Ora-Blend to bring to final volume, and mix well.

2 ASSAY

2.1 Procedure

Solution A: Dissolve 2.7 g of monobasic potassium phosphate in 1000 mL of water. Add 6.5 mL of triethylamine, and adjust with phosphoric acid to a pH of 2.0.

Mobile phase: Acetonitrile and Solution A (20:80). Filter, and degas.

Diluent: 0.1 M hydrochloric acid

Standard solution: 0.4 mg/mL of USP Lamotrigine RS in Diluent

Sample solution: Shake thoroughly each bottle of Oral Suspension. Transfer 4 mL of Oral Suspension into a 10 mL volumetric flask, dilute with Diluent to volume, and mix well.

2.2 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 270 nm

Column: 4.6-mm × 25-cm; 5-μm packing L1

Flow rate: 1.0 mL/min

Injection volume: 5 μL

2.3 System suitability

Sample: Standard solution

[Note—The retention time for lamotrigine is about 9.8 min.]

2.4 Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0% for replicate injections

2.5 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of lamotrigine (C₉H₇Cl₂N₅) in the portion of Oral Suspension taken:

Result = (r_U/r_S)x(C_S/C_U) × 100

r_U = peak response of lamotrigine from the Sample solution

r_S = peak response of lamotrigine from the Standard solution

C_S = concentration of lamotrigine in the Standard solution (mg/mL)

C_U = nominal concentration of lamotrigine in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

3 SPECIFIC TESTS

pH 〈791〉: 4.0–5.0

4 ADDITIONAL REQUIREMENTS

Packaging and Storage: Package in tight, light-resistant containers. Store at controlled room temperature or 2°–8°.

Labeling: Label it to indicate that it is to be well-shaken before use, and to state the Beyond-Use Date.

Beyond-Use Date: NMT 90 days after the date on which it was compounded when stored at controlled room temperature or 2°–8°

USP Reference Standards 〈11〉

USP Lamotrigine RS