Tretinoin

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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C₂₀H₂₈O₂       300.44

Retinoic acid;

all-trans-Retinoic acid CAS RN^®: 302-79-4; UNII: 5688UTC01R.

1 DEFINITION

Tretinoin contains NLT 97.0% and NMT 103.0% of tretinoin (C₂₀H₂₈O₂), calculated on the dried basis.

Avoid exposure to strong light, and use low-actinic glassware in the performance of the following procedures.

2 IDENTIFICATION

Change to read:

A. ^▲SPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 197M_{▲(CN 1-May-2020)}

Change to read:

B. ^▲SPECTROSCOPIC IDENTIFICATION TESTS (197), Ultraviolet-Visible Spectroscopy: 1970_{▲(CN 1-May-2020)}

Analytical wavelength: 352 nm

Medium: Dilute 1 mL of 0.01 N hydrochloric acid with isopropyl alcohol to 1000 mL

Sample solution: 4 µg/mL in Medium

Acceptance criteria: Absorptivities do not differ by more than 3.0%, calculated on the dried basis.

3 ASSAY

PROCEDURE

Sample: 240 mg of Tretinoin

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N sodium methoxide VS

Endpoint detection: Visual

Analysis: Dissolve the Sample in 50 mL of dimethylformamide, and add 3 drops of a 1-in-100 solution of thymol blue in dimethylformamide. Titrate with Titrant to a greenish endpoint. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N sodium methoxide is equivalent to 30.04 mg of tretinoin (C₂₀H₂₈O₂).

Acceptance criteria: 97.0%-103.0% on the dried basis

4 IMPURITIES

4.1 RESIDUE ON IGNITION (281)

NMT 0.1%

4.2 LIMIT OF ISOTRETINOIN

Mobile phase: Isooctane, isopropyl alcohol, and glacial acetic acid (99.65:0.25:0.1)

System suitability stock solution: 250 µg/mL of USP Tretinoin RS in isooctane prepared as follows. Dissolve a quantity of USP Tretinoin RS in a minimum amount of methylene chloride, and add a suitable amount of isooctane to the known concentration.

Standard stock solution: 250 µg/mL of USP Isotretinoin RS in isooctane prepared as follows. Dissolve a quantity of USP Isotretinoin RS in a minimum amount of methylene chloride, and add a suitable amount of isooctane to the known concentration.

System suitability solution: Transfer 5 mL of Standard stock solution into a 100-mL volumetric flask, and add System suitability stock solution to volume.

Standard solution: 12.5 µg/mL of USP Isotretinoin RS in isooctane from Standard stock solution

Sample solution: Transfer 25 mg of Tretinoin into a 100-ml volumetric flask. Dissolve in a minimum amount of methylene chloride, and add isooctane to volume.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 352 nm

Column: 4.0-mm x 25-cm; packing L3

Flow rate: 1 mL/min

Injection volume: 20 µL

System suitability

Sample: System suitability solution

[NOTE-The relative retention times for isotretinoin and tretinoin are about 0.84 and 1.00, respectively.]

Suitability requirements

Resolution: NLT 2.0 between isotretinoin and tretinoin

Relative standard deviation: NMT 2.0% for the isotretinoin peak

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of isotretinoin in the portion of Tretinoin taken:

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

r_U = peak response of isotretinoin from the Sample solution

r_S = peak response of isotretinoin from the Standard solution

C_S = concentration of USP Isotretinoin RS in the Standard solution (µg/mL)

C_U = concentration of Tretinoin in the Sample solution (µg/mL)

Acceptance criteria: NMT 5.0%

5 SPECIFIC TESTS

LOSS ON DRYING (731)

Analysis: Dry a sample under vacuum at room temperature for 16 h.

Acceptance criteria: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers, preferably under an atmosphere of an inert gas, protected from light.

USP REFERENCE STANDARDS (11)

USP Isotretinoin RS

USP Tretinoin RS