Clarithromycin Extended-Release Tablets

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 

Clarithromycin Extended-Release Tablets contain NLT 90.0% and NMT 110.0% of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃). 

2 IDENTIFICATION 

A. 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 

Buffer A: 0.067 M monobasic potassium phosphate 

Mobile phase: Methanol and Buffer A (13:7). Adjust with phosphoric acid to a pH of 4.0. Pass through a suitable filter. Standard stock solution: 625 µg/mL of clarithromycin from USP Clarithromycin RS in methanol. Shake and sonicate, if necessary, to facilitate dissolution. 

Standard solution: 125 µg/mL of clarithromycin in Mobile phase from Standard stock solution. Pass through a suitable filter. System suitability stock solution: 625 µg/mL of USP Clarithromycin Related Compound A RS in methanol 

System suitability solution: 125 µg/mL of USP Clarithromycin Related Compound A RS from System suitability stock solution and 125 µg/mL of clarithromycin from Standard stock solution in Mobile phase 

Sample stock solution: Transfer nominally 2000 mg of clarithromycin from finely powdered Tablets to a 500-mL volumetric flask with the aid of methanol. Add about 350 mL of methanol, and shake by mechanical means for 30 min. Dilute with methanol to volume, and sonicate for 30 min. Cool to room temperature, and allow to stand for at least 16 h. Mix, allow any insoluble matter to settle, and use the supernatant. 

Sample solution: Transfer 3.0 mL of the Sample stock solution to a 100-mL volumetric flask, and dilute with Mobile phase to volume. Pass through a suitable filter. 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 210 nm 

Columns 

Guard (optional): Packing L1 

Analytical: 4.6-mm × 15-cm; packing L1 

Column temperature: 50° 

Flow rate: 1 mL/min 

Injection volume: 20–50 µL 

System suitability 

Samples: Standard solution and System suitability solution 

[Note—The relative retention times for clarithromycin and clarithromycin related compound A are about 0.75 and 1.0, respectively.] Suitability requirements 

Resolution: NLT 2.0 between clarithromycin and clarithromycin related compound A, System suitability solution 

Tailing factor: 0.9–1.5, Standard solution 

Relative standard deviation: NMT 2.0%, Standard solution 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) in the portion of Tablets taken: 

Result = (r_U/r_S) × (C_S/C_U) × 100 

r_U = peak response from the Sample solution  

r_S = peak response from the Standard solution 

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

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

Acceptance criteria: 90.0%–110.0% 

4 PERFORMANCE TESTS 

Change to read: 

Dissolution 〈711〉 

Test 1 

Buffer B: Dissolve 816.5 g of monobasic potassium phosphate and 48 g of sodium hydroxide in about 4 L of water, mix, and dilute with water to 20 L. Adjust with either concentrated phosphoric acid or 1 N sodium hydroxide to a pH of 6.0 ± 0.05. 

Medium: Buffer B; 900 mL 

Apparatus 2: 75 rpm 

Times: 30, 45, 60, and 120 min 

Standard solutions: Prepare ve solutions of USP Clarithromycin RS dissolved in acetonitrile and diluted with Medium, with known concentrations over a range of about 60–600 µg/mL. 

Sample solution: Use portions of the solution under test passed through a polyethylene filter of 35-µm pore size. 

Chromatographic system: Proceed as directed in the Assay, except for the Injection volume. 

Injection volume: 50 µL 

Analysis 

Samples: Standard solutions and Sample solution 

Perform a linear regression analysis to generate a standard curve using the peak area of each Standard solution versus its concentration. Determine the percentage of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at each specified time

interval, using the peak area of each Sample solution and the linear regression statistics for the Standard solutions. Tolerances: The percentages of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at the times specified conform to Table 1. 

Table 1 

Test 2: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 2. 

Buffer C: 0.05 M phosphate buffer with a pH of 6.8, containing 0.5% of sodium lauryl sulfate 

Buffer D: 9.2 g/L of monobasic sodium phosphate monohydrate in water; adjusted with phosphoric acid to a pH of 2.5 prior to nal dilution Medium: Buffer C; 900 mL, degassed by sonication and vacuum 

Apparatus 1: 100 rpm 

Times: 2, 12, and 24 h 

Mobile phase: Methanol and Buffer D (65:35) 

Standard solution: 0.56 mg/mL of USP Clarithromycin RS in a solution of methanol and Medium (1 in 10). Dissolve first in methanol using 10% of the nal volume, and dilute with Medium to volume. 

Sample solution: Centrifuge the solution under test at 2500 rpm for 10 min. 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 210 nm 

Column: 4.6-mm × 15-cm; 5-µm packing L1 

Column temperature: 50° 

Flow rate: 1 mL/min 

Injection volume: 5 µL 

System suitability 

Sample: Standard solution 

Suitability requirements 

Tailing factor: NMT 2.0 

Relative standard deviation: NMT 2.0% 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at each time point (Q_T): 

Q₂ = (r_U/r_S) × (C_S /L) × V × 100 

Q₁₂ = [Q₂ × (V_S/V)] + [(r_U/r_S) × (C_S /L) × (V − V_S) × 100] 

Q₂₄ = [Q₂ × (V_S/V)] + [Q₁₂ × V_S/(V − 2V_S)] + [(r_U/r_S) × (C_S /L) × (V − 2V_S) × 100] 

r_U = peak response from the Sample solution 

r_S = peak response from the Standard solution

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

L = label claim (mg/Tablet) 

V = volume of Medium, 900 mL 

V_S = volume of the sample withdrawn at each time point (mL) 

Tolerances: See Table 2. 

Table 2 

The percentages of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at the times specified conform to Dissolution 〈711〉, 

Acceptance Table 2. 

Test 3: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 3. 

Buffer E: Dissolve 3.59 g of sodium acetate trihydrate and 11.0 mL of 2 N acetic acid in 1000 mL of water. Adjust with 2 N acetic acid to a pH of 4.75. 

Buffer F: 9.12 g/L of monobasic potassium phosphate in water 

Medium: Buffer E; 1000 mL 

Apparatus 1: 10 mesh; 50 rpm 

Times: 1, 2, 4, 8, and 12 h 

Mobile phase: Methanol and Buffer F (65:35). Adjust with phosphoric acid to a pH of 4.0. 

Standard stock solution: 625 µg/mL of clarithromycin from USP Clarithromycin RS in methanol. Shake and sonicate, if necessary, to dissolve. 

Standard solution: 125 µg/mL of clarithromycin from Standard stock solution in Mobile phase 

System suitability stock solution: 625 µg/mL of USP Clarithromycin Related Compound A RS in methanol System suitability solution: 125 µg/mL of clarithromycin related compound A from System suitability stock solution and 125 µg/mL of clarithromycin from Standard stock solution in Mobile phase 

Sample solution: Withdraw 10 mL of the solution under test from each vessel and replace with 10 mL of Medium. Transfer 3 mL of the withdrawn solution to a 25-mL volumetric flask, and dilute with Mobile phase to volume. Pass through a filter of 0.45-µm pore size. Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 210 nm 

Column: 4.6-mm × 15-cm; 5-µm packing L1 

Column temperature: 50° 

Flow rate: 1 mL/min 

Injection volume: 50 µL 

System suitability 

Samples: Standard solution and System suitability solution 

[Note—The relative retention times for clarithromycin and clarithromycin related compound A are about 0.75 and 1.0, respectively.] Suitability requirements 

Resolution: NLT 2.0 between clarithromycin and clarithromycin related compound A, System suitability solution Tailing factor: 0.9–2, Standard solution 

Relative standard deviation: NMT 2.0%, Standard solution 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at each time point (Q_T): 

Q₁ = (r_U/r_S) × (C_S /L) × V × 100 

Q₂ = [Q₁ × (V_S/V)] + [(r_U/r_S) × (C_S /L) × (V − V_S) × 100] 

Q₄ = [Q₁ × (V_S/V)] + [Q₂ × V_S/(V − 2V_S)] + [(r_U/r_S) × (C_S /L) × (V − 2V_S) × 100] 

Q₈ = [Q₁ × (V_S/V)] + [Q₂× V_S/(V − 2V_S)] + [Q₄ × V_S/(V − 3V_S)] + [(r_U/r_S) × (C_S /L) × (V − 3V_S) × 100]

Q₁₂ = [Q₁ × (V_S/V)] + [Q₂ × V_S/(V − 2V_S] + [Q₄ × V_S/(V − 3V_S)] + [Q₈ × V_S/(V − 4V_S)] + [(r_U/r_S) × (C_S /L) × (V − 4V_S) × 100]

r_U = peak response from the Sample solution 

r_S = peak response from the Standard solution

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

L = label claim (mg/Tablet) 

V = volume of Medium, 1000 mL 

V_S = volume of the sample withdrawn at each time point (mL) 

`Tolerances: See Table 3. 

Table 3 

The percentages of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at the times specified conform to Dissolution 〈711〉, 

Acceptance Table 2. 

Test 4: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 4. 

Buffer G: 6.8 g/L of monobasic potassium phosphate and 0.18 g/L of sodium hydroxide in water. Adjust with dilute sodium hydroxide or phosphoric acid to a pH of 6.0 ± 0.1. 

Buffer H: 6.8 g/L of monobasic potassium phosphate in water. Adjust with dilute sodium hydroxide or phosphoric acid to a pH of 4.5 ± 0.1. Medium: Buffer G; 900 mL 

Apparatus 2: 50 rpm 

Times: 2, 4, 8, and 12 h 

Mobile phase: Methanol and Buffer H (64:36) 

Standard solution: 0.4 mg/mL of USP Clarithromycin RS in methanol and Medium (4:96). Dissolve first in Medium, using 60% of the nal volume. Sonicate about 10 min until dissolved. Add methanol, using 4% of the nal volume. Dilute with Medium to volume. Sample solution: Use the solution under test, passed through a suitable filter of 0.45-µm pore size. 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 203 nm 

Column: 4.0-mm × 12.5-cm; 5-µm packing L7 

Column temperature: 30° 

Flow rate: 1 mL/min 

Injection volume: 20 µL 

System suitability 

Sample: Standard solution 

Suitability requirements 

Tailing factor: NMT 2.0 

Relative standard deviation: NMT 2.0% 

Analysis 

Samples: Standard solution and Sample solution 

Determine the concentration, in mg/mL, of clarithromycin (C₃₈H₆₉NO₁₃) in the Sample solution at each time point (Q_T):

Result = (r_U/r_S) × C_S × 100 

r_U = peak response from the Sample solution  

r_S = peak response from the Standard solution 

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

 Calculate the percentage of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at each time point (Q_T): 

Q₂ = (r_U/r_S) × (C_S /L) × V × 100 

Q₄ = [Q₂ × (V_S/V)] + [(r_U/r_S) × (C_S /L) × (V − V_S) × 100] 

Q₈ = [Q₂ × (V_S/V)] + [Q₄ × V_S/(V − 2V_S)] + [(r_U/r_S) × (C_S /L) × (V − 2V_S) × 100] 

Q₁₂ = [Q₂ × (V_S/V)] + [Q₄× V_S/(V − 2V_S)] + [Q₈ × V_S/(V − 3V_S)] + [(r_U/r_S) × (C_S /L) × (V − 3V_S) × 100]

r_U = peak response from the Sample solution 

r_S = peak response from the Standard solution

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

L = label claim (mg/Tablet) 

V = volume of Medium, 900 mL 

V_S = volume of the sample withdrawn at each time point (mL) 

Tolerances: See Table 4. 

Table 4 

The percentages of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at the times specified conform to Dissolution 〈711〉,

Acceptance Table 2. 

Test 5: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 5. 

Medium: Phosphate buffer, pH 6.0 (6.8 g/L of monobasic potassium phosphate and 0.18 g/L of sodium hydroxide in water. Adjust with dilute sodium hydroxide or phosphoric acid to a pH of 6.0 ± 0.1.); 900 mL 

Apparatus 2: 50 rpm, with sinker (see Dissolution 〈711〉, Figure 2a) 

Times: 2, 4, 8, and 14 h 

Buffer: 9.11 g/L of monobasic potassium phosphate in water. Adjust with dilute sodium hydroxide or phosphoric acid to a pH of 2.5 ± 0.05. Mobile phase: Acetonitrile and Buffer (55:45) 

Standard solution: 0.55 mg/mL of USP Clarithromycin RS in Medium. Sonicate to dissolve prior to dilution to nal volume. Sample solution: Pass a portion of the solution under test through a suitable filter of 0.22-µm pore size. Replace the portion of solution withdrawn with an equal volume of Medium. 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 210 nm 

Column: 2.1-mm × 10-cm; 1.7-µm packing L1 

Column temperature: 50° 

Flow rate: 0.25 mL/min 

Injection volume: 2 µL 

System suitability 

Sample: Standard solution 

Suitability requirements 

Relative standard deviation: NMT 2.0% 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the concentration (C ) of clarithromycin (C₃₈H₆₉NO₁₃) in the sample withdrawn from the vessel at each time point (i):

Result_i = (r_U/r_S) × C_S × 100 

r_U = peak response from the Sample solution  

r_S = peak response from the Standard solution 

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

Calculate the percentage of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at each time point (i):

Result₁ = C₁ × V × (1/L) × 100 

Result₂ = [(C₂ × V) + (C₁ × V_S )] × (1/L) × 100 

Result₃= {(C₃ × V) + [(C₂ + C₁) × V_S ]} × (1/L) × 100 

Result₄ = {(C₄ × V) + [(C₃ + C₂ + C₁) × V_S ]} × (1/L) × 100 

C_i = concentration of clarithromycin in the portion of sample withdrawn at the specified time point (mg/mL) i 

V = volume of Medium, 900 mL 

L = label claim (mg/Tablet) 

V_S = volume of the Sample solution withdrawn at each time point and replaced with Medium (mL) S 

Tolerances: See Table 5. 

Table 5 

The percentages of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at the times specified conform to Dissolution 〈711〉, 

Acceptance Table 2. 

Test 6: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 6. 

Medium: 0.05 M sodium phosphate buffer, pH 6.8 with 5 g/L of sodium dodecyl sulfate, prepared as follows. Dissolve 38.3 g of sodium phosphate, tribasic in 100 mL of water and transfer to a 2-L container containing 1800 mL of water. Add 12.5 mL of hydrochloric acid and adjust with sodium hydroxide or hydrochloric acid to a pH of 6.8. Dilute with water to volume. To each liter of this solution, add 5 g of sodium dodecyl sulfate and dissolve by stirring NLT 20 min; 900 mL, deaerated. 

Apparatus 1: 100 rpm 

Times: 2, 12, and 24 h 

Buffer: Dissolve 9.2 g of sodium phosphate, monobasic in 860 mL of water, and adjust with phosphoric acid to a pH of 2.5. Dilute with water to 1000 mL. 

Mobile phase: Methanol and Buffer (65:35) 

Standard solution: 0.56 mg/mL of USP Clarithromycin RS prepared as follows. Transfer an appropriate quantity of USP Clarithromycin RS to a suitable volumetric flask. Add 10% of the flask volume of methanol and sonicate to dissolve, if necessary. Dilute with Medium to volume. 

Sample solution: Centrifuge a portion of the solution under test and use the supernatant. [Note—The use of a centrifuge speed at 2500 rpm for 10 min may be suitable.] 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 210 nm 

Column: 4.6-mm × 15-cm; 5-µm packing L1 

Column temperature: 50° 

Flow rate: 1 mL/min 

Injection volume: 5 µL 

Run time: NLT 1.7 times the retention time of clarithromycin 

System suitability 

Sample: Standard solution 

Suitability requirements 

Relative standard deviation: NMT 2.0% 

Tailing factor: NMT 2.0 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the concentration (C ) of clarithromycin (C₃₈H₆₉NO₁₃) in the sample withdrawn from the vessel at each time point (i): 

Result_i = (r_U/r_S) × C_S × 100 

r_U = peak response of clarithromycin from the Sample solution

r_S = peak response of clarithromycin from the Standard solution

C_S = concentration of USP Clarithromycin RS from the Standard solution (mg/mL)

Calculate the percentage of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at each time point (i):

Result₁ = C₁ × V × (1/L) × 100 

Result₂ = {[C₂ × (V - V_S) + (C₁ × V_S )] } × (1/L) × 100 

Result₃= ({C₃ × [V − (2 × V_S)]} + [(C₂ + C₁) × V_S]) × (1/L) × 100

C_i = concentration of clarithromycin in the portion of sample withdrawn at the specified time point i (mg/mL) 

V = volume of Medium, 900 mL 

L = label claim (mg/Tablet) 

V_S = volume of the Sample solution withdrawn at each time point from the Medium (mL) 

Tolerances: See Table 6. 

Table 6 

The percentages of the labeled amount of clarithromycin (C₃₈H₆₉NO₁₃) dissolved at the times specified conform to Dissolution 〈711〉, 

Acceptance Table 2. 

Uniformity of Dosage Units 〈905〉: Meet the requirements 

5 IMPURITIES 

Change to read: 

Organic Impurities 

Solution A: 4.76 g/L of monobasic potassium phosphate in water. Adjust with dilute phosphoric acid or potassium hydroxide to a pH of 4.4 ± 0.05. 

Solution B: Acetonitrile 

Mobile phase: See Table 7. 

Table 7 

Diluent: Acetonitrile and water (50:50) 

System suitability solution: 3.0 mg/mL of USP Clarithromycin Identity RS in acetonitrile and water (1:1). Dissolve first in acetonitrile, using 50% of the nal volume, sonicate, and dilute with water to volume. Pass this solution through a suitable filter of 0.45-µm pore size. Standard stock solution: 0.38 mg/mL of USP Clarithromycin RS in acetonitrile and water (1:1). Dissolve first in acetonitrile, using 50% of the nal volume, sonicate in cool water to dissolve it completely, and dilute with water to volume. 

Standard solution: 0.015 mg/mL of USP Clarithromycin RS from Standard stock solution in Diluent. Pass this solution through a suitable filter of 0.45-µm pore size. Store this solution at 10° and discard after 24 h. 

Sensitivity solution: 0.003 mg/mL of USP Clarithromycin RS from Standard solution in Diluent. Store this solution at 10° and discard after 24 h. 

Sample solution: Nominally 3.0 mg/mL of clarithromycin from NLT 20 Tablets prepared as follows. Transfer a portion of the finely powdered Tablets, equivalent to 300 mg of clarithromycin, to a 100-mL volumetric flask containing 25 mL of acetonitrile. Add another 25 mL of acetonitrile and sonicate for about 10 min in cool water. Then add 25 mL of water, sonicate for about 2 min, and dilute with water to volume. Pass through a suitable filter of 0.45-µm pore size and discard the first few milliliters of the filtrate. Store this solution at 10° and discard after 24 h. 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 205 nm 

Column: 4.6-mm × 15-cm; 3.5-µm packing L1 

Temperatures 

Autosampler: 10° 

Column: 40° 

Flow rate: 1.1 mL/min 

Injection volume: 10 µL 

Run time: NLT 3 times the retention time of clarithromycin 

System suitability 

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

[Note—See Table 8 for relative retention times.] 

Suitability requirements 

Peak-to-valley ratio: NLT 3.0 between clarithromycin and clarithromycin impurity D, System suitability solution 

Calculate the Peak-to-valley ratio as follows: 

Result = H_P/H_V 

H_P = height above the baseline of the clarithromycin impurity D peak 

H_V = height above the baseline of the lowest point of the curve separating the clarithromycin impurity D peak from the clarithromycin peak 

Tailing factor: NMT 2.5, Standard solution 

Relative standard deviation: NMT 5.0%, Standard solution 

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

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of each individual impurity in the portion of Tablets taken: 

Result = (r_U/r_S) × (C_S/C_U) x (1/F) × 100 

r_U = peak response of each impurity from the Sample solution

r_S = peak response of clarithromycin from the Standard solution 

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

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

F = relative response factor (see Table 8)

Acceptance criteria: See Table 8. (RB 1-Dec-2023) Not more than four impurities exceed 0.4%. The reporting threshold is 0.1%. Disregard the peaks eluting before impurity I and after impurity H. 

Table 8

^a3-O-Decladinosyl-6-O-methylerythromycin A.

^b 2-Demethyl-2-(hydroxymethyl)-6-O-methylerythromycin A. 

^c Process impurities that are controlled in the drug substance are not to be reported. They are not to be included in total impurities. They are listed here for information only. 

^d 6-O-Methylerythromycin A (E)-9-oxime. 

^e 3″-N-Demethyl-6-O-methylerythromycin A. 

^f 6,11-Di-O-methylerythromycin A. 

^g 6,12-Di-O-methylerythromycin A. 

^h 6-O-Methylerythromycin A (E)-9-(O-methyloxime). 

ⁱ 3″-N-Demethyl-3′-N-formyl-6-O-methylerythromycin A. 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in well-closed containers, protected from light. Store at 25°, excursions permitted between 15° and 30°. Labeling: When more than one Dissolution test is given, the labeling states the Dissolution test used only if Test 1 is not used. USP Reference Standards 〈11〉 

USP Clarithromycin RS 

USP Clarithromycin Related Compound A RS 

6,11-Di-O-methylerythromycin A. 

C₃₉H₇₁NO₁₃ 762.00 

USP Clarithromycin Identity RS 

Contains a mixture of other impurities and the following: 

Clarithromycin. 

Clarithromycin impurity D; 

3″-N-Demethyl-6-O-methylerythromycin A. 

C₃₇H₆₇NO₁₃    733.93