Doxycycline

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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2-Naphthacenecarboxamide, 4-(dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,5,10,12,12a-pentahydroxy-6-methyl-1,11-dioxo-, [4S-(4α,4aα,5α,5aα,6α,12aα)]-, monohydrate;

(4S,4aR,5S,5aR,6R,12aS)-4-(Dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,5,10,12,12a-pentahydroxy-6-methyl-1,11-dioxo-2-naphthacenecarboxamide monohydrate CAS RN^®: 17086-28-1; UNII: N12000U13O.

Anhydrous CAS RN^®: 564-25-0; UNII: 334895S862.

1 DEFINITION

Doxycycline has a potency equivalent to NLT 880 µg/mg and NMT 980 µg/mg of doxycycline (C₂₂H₂₄N₂O₈).

2 IDENTIFICATION

A. SPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 197A

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

PROCEDURE

Protect solutions containing doxycycline from light

Solution A: Transfer 3.1 g of monobasic potassium phosphate and 0.5 g of of edetate disodium to a 1000-mL volumetric flask. Add about 850 ml of water and 0.5 ml of triethylamine, and mix. Dilute with water to volume and adjust with 1 N sodium hydroxide to a pH of 8.5 plus/minus 0.1 .

Solution B: Methanol

Mobile phase: See Table 1.

Diluent: 0.01 N hydrochloric acid

Standard solution: 0.1 mg/ml. of USP Doxycycline Monohydrate RS in Diluent. Sonicate as needed to dissolve.

Sample solution: 0.1 mg/mL of Doxycycline in Diluent. Sonicate as needed to dissolve.

Chromatographic system

(See Chromatography (621), System Suitability.)

USP-NF Doxycycline

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Mode: LC

Detector: UV 270 nm

Column: 2.1-mm x 5-cm, 1.7-µm packing LZ

Column temperature: 60°

Flow rate: 0.6 mL/min

Injection volume: 5 µL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 1.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the quantity of doxycycline (C₂₂H₂₄N₂O₈) 8 in µg/mg, in the portion of Doxycycline taken:

Result = (r_U/(r_S) × (C_S /C_U) × P 

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of USP Doxycycline Monohydrate RS, in the Stardard solution (mg/ml)

C_U = nominal concentration of doxycycline in the Sample solation (mg/ml)

P = potency of doxycycline in USP Doxycycline Monohydrate RS (µg/mg)

4 IMPURITIES

Change to read:

ORGANIC IMPURITIES

Mobile phase, Diluent, and Chromatographic system: Proceed as directed in the Assay.

System suitability stock solution 1: 1 mg/ml each of USP Methacycline Hydrochloride RS and USP Doxycycline Related Compound A RS in Diluent

System suitability stock solution 2: 1.2 mg/mL of USP Doxycycline Hyclate RS in Diluent

System suitability solution: Transfer 5 mL of System suitability stock solution 2 to a 25-ml volumetric flask, heat on a steam bath for 60 min, and evaporate to dryness on a hot plate, taking care not to char the residue. Dissolve the residue in Diluent, add 0.5 ml. of System suitability stock solution 1, and dilute with Diluent to volume Pass the solution through a suitable filter and use the filtrate. This solution contains a mixture of 4-epidoxycycline, methacycline, doxycycline related compound A, and doxycycline. When stored in a refrigerator, this solution may be used for 14 days.

Sensitivity solution: 0.001 mg/mL of USP Doxycycline Monohydrate RS in Diluent

Standard solution: 0.002 mg/ml, each of USP Doxycycline Monohydrate RS and USP Methacycline Hydrochloride RS in Diluent

Sample solution: 2 mg/mL of Doxycycline in Diluent. Sonicate as needed to dissolve.

System suitability

Samples: System suitability solution, Sensitivity solution, and Standard solution

Suitability requirements

Resolution: NLT 1.5 between methacycline and 4-epidoxycycline, NLT 1:5 between 4-epidoxycycline and doxycycline related compound A

NLT 2.0 between doxycycline related compound A and doxycycline, System suitability solution

Relative standard deviation: NMT 5.0% each for the doxycycline and methacycline peaks, Standard solution

Signal-to-noise ratio: NLT 10, Sensitivity solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of methacycline in the portion of Doxycycline taken:

Result = (r_U/(r_S) × (C_S /C_U) × P x F x 100

r_U = peak response  of methacycline from the Sample solution

r_S = peak response  of methacycline from the Standard solution

C_S = concentration of USP Methacycline Hydrochloride RS, in the Stardard solution (mg/ml)

C_U = concentration of doxycycline in the Sample solation (mg/ml)

P = potency of doxycycline in USP Methacycline Hydrochloride RS (µg/mg)

F = conversion factor, 0.001 mg/µg

Calculate the percentage of 4-epidoxycycline, doxycycline related compound A, doxycycline related compound F, and any individual unspecied impurity in the portion of Doxycycline taken:

Result = (r_U/(r_S) × (C_S /C_U) × P x F₁/F₂ x 100

^a(4R,4aR,5S,5aR,6R,12aS)-4-(Dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,5,10,12,12a-pentahydroxy-6-methyl-1,11-dioxo-2-
naphthacenecarboxamide. Main degradation product.

^b (4S,4aR,5S,5aR,6R,12aS)-2-Acetyl-4-(dimethylamino)-3,5,10,12,12a-pentahydroxy-6-methyl-4a,5a,6,12a-tetrahydrotetracene-1,11(4H,5H)-
dione.

5 SPECIFIC TESTS

CRYSTALLINITY (695): Meets the requirements.

PH (791)

Sample solution: An aqueous suspension containing 10 mg/ml.

Acceptance criteria: 5.0-6.5

WATER DETERMINATION (921), Method: 3.6%-4.6%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight, light-resistant containers.