Dorzolamide Hydrochloride and Timolol Maleate Ophthalmic Solution

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

Dorzolamide Hydrochloride and Timolol Maleate Ophthalmic Solution is a sterile, isotonic, buffered, slightly viscous, aqueous solution of Dorzolamide Hydrochloride and Timolol Maleate. It contains NLT 90.0% and NMT 110.0% of the labeled amount of dorzolamide (C₁₀H₁₆N₂O₄S₃) and NLT 90.0% and NMT 110.0% of the labeled amount of timolol (C₁₃H₂₄N₄O₃S). It may contain a suitable preservative.

2 IDENTIFICATION

Change to read:

A. The UV spectrum of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay, Procedure for Dorzolamide _{(USP 1-Dec-2021)}

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

C. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay, Procedure for Timolol,

Add the following:

D. The UV spectrum of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay, Procedure for Timolol _{(USP 1-Dec-2021)}

3 ASSAY

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3.1 PROCEDURE FOR DORZOLAMIDE

Solution A: Acetonitrile

Solution B: 0.2% (v/v) phosphoric acid in water

Mobile phase: See Table 1.

Table 1

Diluent: Acetonitrile and Solution B (5:95)

Standard solution: 0.11 mg/mL of USP Dorzolamide Hydrochloride RS and 0.5 µg/mL each of USP Dorzolamide Related Compound B RS and

USP Dorzolamide Related Compound D RS in Diluent

Sample solution: Nominally 0.1 mg/mL of dorzolamide in Diluent, from Ophthalmic Solution

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 253 nm. For Identication A, use a diode array detector in the range of 200–400 nm. _{(USP 1-Dec-2021)}

Column: 4.6-mm × 25-cm; 5-µm packing L7

Flow rate: 1.2 mL/min

Injection volume: 20 µL

System suitability

Sample: Standard solution

[NOTE-See Table 2 for the relative retention times.]

Suitability requirements

Resolution: NLT 3.0 between dorzolamide and dorzolamide related compound D; NLT 3.0 between dorzolamide and dorzolamide related compound B

Relative standard deviation: NMT 2.0% for dorzolamide

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of dorzolamide (C₁₀H₁₆N₂O₄S₃) in the portion of Ophthalmic Solution taken: 162

Result = (r_u /r_s ) × (C_s /C_u ) × (M_r1 /M_r2 ) × 100

r_u = peak response of dorzolamide from the Sample solution

r_s = peak response of dorzolamide from the Standard solution

C_s = concentration of USP Dorzolamide Hydrochloride RS in the Standard solution (mg/mL)

C_u = nominal concentration of dorzolamide in the Sample solution (mg/mL)

M_r1 = molecular weight of dorzolamide, 324.43 _{(USP 1-Dec-2021)}

M_r2 = molecular weight of dorzolamide hydrochloride, 360.89 _{(USP 1-Dec-2021)}

Acceptance criteria: 90.0%–110.0%

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3.2 PROCEDURE FOR TIMOLOL

Buffer: Transfer 22 g of sodium phosphate, monobasic into a 2000-mL volumetric flask. Dissolve in 1995 mL of water, and adjust with phosphoric acid to a pH of 2.8. Dilute with water to volume.

Mobile phase: Methanol and Buffer (40:60)

System suitability solution: Transfer 88 mg of USP Timolol Maleate RS into a 50-mL volumetric flask. Transfer 8 mL of 0.1 M sodium hydroxide into the flask, mix, and heat at 70° for 15 h. Dilute with Mobile phase to volume, and mix well. Transfer 5 mL of this solution into a 25-ml volumetric flask, and add 28 mg of USP Dorzolamide Hydrochloride RS into the same flask. Dilute with Mobile phase to volume. [NOTE

-The preparation generates timolol impurity G and timolol related compound B.]

Standard solution: 0.35 mg/mL of USP Timolol Maleate RS in Mobile phase

Sample solution: Nominally 0.25 mg/mL of timolol in Mobile phase, from Ophthalmic Solution

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 295 nm. For Identification D, use a diode array detector in the range of 200-400 nm. _{(USP 1-Dec-2021)}

Column: 4.6-mm x 25-cm; 5-µm packing 11

Column temperature: 40"

Flow rate: 1 mL/min

Injection volume: 20 µL

System suitability

Sample: System suitability solution

[NOTE-See Table 3 for the relative retention times.]

Suitability requirements

Resolution: NLT 1.5 between timolol impurity G and timolol related compound B

Relative standard deviation: NMT 2.5% for timolol for 5 replicate injections

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of timolol (C₁₃H₂₄N₄O₃S) in the portion of Ophthalmic Solution taken:

Result = (r_u /r_s ) × (C_s /C_u ) × (M_r1 /M_r2 ) × 100

r_u = peak response of timolol from the Sample solution

r_s = peak response of timolol from the Standard solution

C_s = concentration of USP Timolol Maleate RS in the Standard solution (mg/mL)

C_u = nominal concentration of timolol in the Sample solution (mg/mL)

M_r1 = molecular weight of timolol, 316.42

M_r2 = molecular weight of timolol maleate, 432.49

Acceptance criteria: 90.0%–110.0%

4 IMPURITIES

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4.1 ORGANIC IMPURITIES, DORZOLAMIDE HYDROCHLORIDE

Solution A, Solution B, (USP 1-Dec-2021) Mobile phase, Diluent, (USP 1-Dec-2021) Sample solution, and Chromatographic

system: Proceed as directed in the Assay, Procedure for Dorzolamide.

System suitability solution: Use the Standard solution as prepared in the Assay, Procedure for Dorzolamide.

Standard solution: 0.5 µg/mL each of USP Dorzolamide Related Compound B RS and USP Dorzolamide Related Compound D RS in Diluent _{(USP 1-Dec-2021)}

System suitability

Sample: System suitability solution (USP 1-Dec-2021)

Suitability requirements

Resolution: NLT 3.0 between dorzolamide and dorzolamide related compound D; NLT 3.0 between dorzolamide and dorzolamide related compound B

Relative standard deviation: NMT 2.0% for dorzolamide

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of dorzolamide related compound D in the portion of Ophthalmic Solution taken:

Result = (r_u /r_s ) × (C_s /C_u ) × (M_r1 /M_r2 ) × 100

r_u = peak area of dorzolamide related compound D from the Sample solution

r_s = peak area of dorzolamide related compound D from the Standard solution

C_s = concentration of USP Dorzolamide Related Compound D RS in the Standard solution (mg/mL)

C_u = nominal concentration of dorzolamide in the Sample solution (mg/mL)

M_r1 = molecular weight of dorzolamide, 324.43 _{(USP 1-Dec-2021)}

M_r2 = molecular weight of dorzolamide related compound D, 332.83 _{(USP 1-Dec-2021)}

Calculate the percentage of dorzolamide related compound B in the portion of Ophthalmic Solution taken:

Result = (r_u /r_s ) × (C_s /C_u ) × (M_r1 /M_r2 ) × 100

r_u = peak area of dorzolamide related compound B from the Sample solution

r_s = peak area of dorzolamide related compound B from the Standard solution

C_s = concentration of USP Dorzolamide Related Compound B RS in the Standard solution (mg/mL)

C_u = nominal concentration of dorzolamide in the Sample solution (mg/mL)

M_r1 = molecular weight of dorzolamide, 324.43 _{(USP 1-Dec-2021)}

M_r2 = molecular weight of dorzolamide related compound B, 360.89 _{(USP 1-Dec-2021)}

Calculate the percentage of each individual unspecied impurity in the portion of Ophthalmic Solution taken:

Result = (r_U /r_T ) × 100

r_U = peak area of each individual unspecied impurity from the Sample solution

r_T = sum of all the peak areas from the Sample solution

Acceptance criteria: See Table 2. The reporting threshold is 0.10%.

Table 2

^a It is the sum of all impurities in Table 2 and dorzolamide maleic acid adducts in Table 5.

Change to read:

4.2 ORGANIC IMPURITIES, TIMOLOL MALEATE

Buffer, _{(USP 1-Dec-2021)} Mobile phase, System suitability solution, and Sample solution: Prepare as directed in the Assay, Procedure for Timolol.

Standard stock solution: Use the Standard solution as prepared in the Assay, Procedure for Timolol.

Standard solution: 3.5 µg/mL of USP Timolol Maleate RS in Mobile phase, from the Standard stock solution

Chromatographic system: Proceed as directed in the Assay, Procedure for Timolol except for the Run time.

Run time: NLT 2 times the retention time of timolol

System suitability

Sample: System suitability solution

Suitability requirements

Resolution: NLT 1.5 between timolol impurity G and timolol related compound B

Relative standard deviation: NMT 2.5% for timolol for 5 replicate injections

Analysis

Samples: Sample solution and Standard solution

Calculate the percentage of each individual impurity in the portion of Ophthalmic Solution taken:

Result = (r_u /r_s ) × (C_s /C_u ) × (M_r1 /M_r2 ) × 100

r_u = peak area of each individual impurity from the Sample solution

r_s = peak area of timolol from the Standard solution

C_s = concentration of USP Timolol Maleate RS in the Standard solution (mg/mL)

C_u = nominal concentration of timolol in the Sample solution (mg/mL)

M_r1 = molecular weight of timolol, 316.42

M_r2 = molecular weight of timolol maleate, 432.49

Acceptance criteria: See Table 3. The reporting threshold is 0.10%.

Table 3

^a 4-Morpholino-1,2,5-thiadiazol-3-ol 1-oxide.

^b 3-(tert-Butylamino)-2-(4-morpholino-1,2,5-thiadiazol-3-yloxy)propan-1-ol.

^c 4-Morpholino-1,2,5-thiadiazol-3-ol.

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4.3 LIMIT OF DORZOLAMIDE MALEIC ACID ADDUCTS

Solution A, Solution B, Diluent, (USP 1-Dec-2021) Standard solution, Sample solution, Chromatographic system, and System

suitability: Proceed as directed in the Assay, Procedure for Dorzolamide.

Mobile phase: See Table 4. Return to original conditions and re-equilibrate the system for 6 min.

Table 4

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of dorzolamide maleic acid adduct in the portion of Ophthalmic Solution taken:

Result = (r_u /r_s ) × (C_s /C_u ) × (M_r1 /M_r2 ) × 100

r_u = peak area of dorzolamide maleic acid adduct from the Sample solution

r_s = peak area of dorzolamide from the Standard solution

C_s = concentration of USP Dorzolamide Hydrochloride RS in the Standard solution (mg/mL)

C_u = nominal concentration of dorzolamide in the Sample solution (mg/mL)

M_r1 = molecular weight of dorzolamide, 324.43 _{(USP 1-Dec-2021)}

M_r2 = molecular weight of dorzolamide hydrochloride, 360.89 _{(USP 1-Dec-2021)}

Acceptance criteria: See Table 5.

Table 5

^a The chromatographic system resolves the two epimers from each other.

^b N-Ethyl-N-[(4S,6S)-6-methyl-7,7-dioxido-2-sulfamoyl-5,6-dihydro-4H-thieno[2,3-b]thiopyran-4-yl]aspartic acid.

5 SPECIFIC TESTS

STERILITY TESTS (71): Meets the requirements

PH (791): 5.4-5.9 at 22°

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OTHER REQUIREMENTS: It meets the requirements in Ophthalmic Products-Quality Tests (771) (USP 1-Dec-2021)

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers protected from light, at controlled room temperature.

Change to read:

USP REFERENCE STANDARDS (11)

USP Dorzolamide Hydrochloride RS

USP Dorzolamide Related Compound B. RS

(4RS,6SR)-4-(Ethylamino)-6-methyl-5,6-dihydro-4H-thieno [2,3-b]thiopyran-2-sulfonamide 7,7-dioxide hydrochloride

C₁₀H₁₆N₂O₄S₃ · HCl          360.89 _{(USP 1-Dec-2021)}

USP Dorzolamide Related Compound D. RS

(4S,6S)-4-Amino-6-methyl-5,6-dihydro-4H-thieno [2,3-b]thiopyran-2-sulfonamide 7,7-dioxide hydrochloride.

C₈H₁₂N₂O₄S₃ · HCl          332.83 _{(USP 1-Dec-2021)}

USP Timolol Maleate RS