Phentermine Hydrochloride Capsules

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

Phentermine Hydrochloride Capsules contain NLT 90.0% and NMT 110.0% of the labeled amount of phentermine hydrochloride (C₁₀H₁₅N·HCI).

2 IDENTIFICATION

A.

Sample solution: Stir a portion of the Capsule contents in acetone to prepare a solution containing a nominal concentration at about 1 mg/mL of phentermine hydrochloride.

Analysis: Filter the Sample solution using an acetone resistant filter. Transfer 1 mL of the clear filtrate to a mortar containing about 200 mg of potassium bromide, triturate with a pestle, and air-dry to allow the acetone to evaporate. Place in an oven at 125° for 30 min to dry the mixture.

Acceptance criteria: The IR absorption spectrum of a potassium bromide dispersion prepared from the residue exhibits maxima only at the same wavelengths as that of a similar preparation of USP Phentermine Hydrochloride RS.

B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

3.1 PROCEDURE

Mobile phase: 1.1 g of sodium 1-heptanesulfonate in 575 mL of water. Add 25 mL of dilute glacial acetic acid (14 in 100) and 400 mL of methanol. Adjust dropwise, if necessary, with glacial acetic acid to a pH of 3.3 ± 0.1. Pass through a membrane filter of 0.5-µm pore size. The volume of methanol may be adjusted to provide a suitable retention time for phentermine hydrochloride (about 8 min).

Diluent: 0.04 M phosphoric acid

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

Sample solution: Remove, as completely as possible, the contents of NLT 20 Capsules, and weigh. Transfer a portion of the mixed powder, nominally equivalent to about 20 mg of phentermine hydrochloride, to a 50-mL volumetric flask. Add 40 mL of Diluent, and sonicate for 15 min. Dilute with Diluent to volume, and mix. Pass through a membrane filter of 0.5-µm pore size, discarding the first few mL of the filtrate.

3.2 Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 254 nm

OFF Column: 3.9-mm x 30-cm; packing L1

Flow rate: 2 mL/min

Injection volume: 50 µL

3.3 System suitability

Sample: Standard solution

Suitability requirements

Relative standard deviation: NMT 2.0%

3.4 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of phentermine hydrochloride (C₁₀H₁₅N·HCI) in the portion of Capsules taken:

Result = (r_U/r_S) x (C_S/C_U) x 100

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of USP Phentermine Hydrochloride RS in the Standard solution (mg/mL)

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

Acceptance criteria: 90.0%-110.0%

4 PERFORMANCE TESTS

4.1 DISSOLUTION, Procedure for a Pooled Sample (711)

Medium: Water; 900 mL. Use 500 mL for Capsules containing 15 mg or less of phentermine hydrochloride.

Apparatus 2: 50 rpm

Time: 45 min

Analysis: Determine the amount of phentermine hydrochloride (C₁₀H₁₅N·HCI) dissolved, by using the Procedure set forth in the Assay, making any necessary modifications including concentration of the analyte in the volume of the Sample solution taken.

Tolerances: NLT 75% (Q) of the labeled amount of phentermine hydrochloride (C₁₀H₁₅N·HCI) is dissolved.

4.2 UNIFORMITY OF DOSAGE UNITS (905)

Meet the requirements

5 ADDITIONAL REQUIREMENTS

5.1 PACKAGING AND STORAGE

Preserve in tight containers.

5.2 USP REFERENCE STANDARDS (11)

USP Phentermine Hydrochloride RS