C₁₀H₁₁N₃O₃S = 253.3

pKa₁ ca. 2.5

pKa₂ 5.6

DEFINITION

Sulfamethoxazole contains not less than 99.0 per cent and not more than the equivalent of 101.0 per cent of 4-amino-N-(5-methyl-3-isoxazolyl)benzenesulphonamide, calculated with reference to the dried substance.

CHARACTERS

A white or almost white, crystalline powder, practically insoluble in water, freely soluble in acetone, sparingly soluble in alcohol, slightly soluble in ether. It dissolves in dilute solutions of sodium hydroxide.

C₆H₈N₂O₂S =172.2

pKa₁ 3.2

pKa₂ 10.4

C₆H₇NO₃S = 173.8

pKa₁ < 1

pKa₂ 2.5

C₁₄H₁₈N₄O₃ = 290.3

pKa 7.2

DEFINITION

Trimethoprim contains not less than 98.5 per cent and not more than the equivalent of 101.0 per cent of 5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4-diamine, calculated with reference to the dried substance.

CHARACTERS

A white or yellowish-white powder, very slightly soluble in water, slightly soluble in alcohol.

C₈H₈O₃ = 152.1

pKa = 8.4

A(1%,1cm) 1075, 257 nm in ethanol

DEFINITION

Methyl parahydroxybenzoate contains not less than 99.0 per cent and not more than the equivalent of 100.5 per cent of methyl 4-hydroxybenzoate.

CHARACTERS

A white, crystalline powder or colourless crystals, very slightly soluble in water, freely soluble in alcohol and in methanol.

Aluminii magnesii silicas

DEFINITION

Aluminium magnesium silicate is a mixture of particles with colloidal particle size of montmorillonite and saponite, free from grit and nonswellable ore. It contains not less than 95.0 per cent and not more than 105.0 per cent of the amount of aluminium and magnesium stated on the label.

CHARACTERS

Almost white powder or plates, practically insoluble in water, mineral acids and in organic solvents.

It swells in water to produce a colloidal dispersion.

IDENTIFICATION

A.Fuse 1 g with 2 g of anhydrous sodium carbonate R. Warm the residue with water R and filter. Acidify the filtrate with hydrochloric acid R and evaporate to dryness on a water-bath. 0.25 g of the residue gives the reaction of silicates (2.3.1).

B.Dissolve the remainder of the residue obtained in identification test A in a mixture of 5 ml of dilute hydrochloric acid R and 10 ml of water R. Filter and add ammonium chloride buffer solution pH 10.0 R. A white, gelatinous precipitate is formed. Centrifuge, keep the supernatant for identification C. Dissolve the remaining precipitate in dilute hydrochloric acid R. The solution gives the reaction of aluminium (2.3.1).

C.The supernatant liquid obtained after centrifugation in identification test B gives the reaction of magnesium (2.3.1).

Carmellosum natricum

DEFINITION

Carmellose sodium (carboxymethylcellulose sodium) is the sodium salt of a partly O-carboxymethylated cellulose. It contains not less than 6.5 per cent and not more than 10.8 per cent of sodium (Na), calculated with reference to the dried substance.

CHARACTERS

A white or almost white, granular powder, hygroscopic after drying, practically insoluble in acetone, in ethanol, in ether and in toluene. It is easily dispersed in water giving colloidal solutions.

Glucosum anhydricum

C₆H₁₂O₆ = 180.2

DEFINITION

Anhydrous glucose is D-(+)-glucopyranose.

CHARACTERS

C₆H₈O₇,H₂O = 210.1

DEFINITION

Citric acid monohydrate contains not less than 99.5 per cent and not more than the equivalent of 101.0 per cent of 2-hydroxypropane-1,2,3-tricarboxylic acid, calculated with reference to the anhydrous substance.

CHARACTERS

A white, crystalline powder, colourless crystals or granules, efflorescent, very soluble in water, freely soluble in alcohol, sparingly soluble in ether.

General Notices

Trimethoprim and Sulfamethoxazole Oral Suspension

Definition Co-trimoxazole Oral Suspension is a suspension containing 1.6% w/v of Trimethoprim and 8.0% w/v of Sulfamethoxazole in a suitable flavoured vehicle.

The oral suspension complies with the requirements stated under Oral Liquids and with the following requirements.

Content of trimethoprim, C₁₄H₁₈N₄O₃ 1.44 to 1.76% w/v.

Content of sulfamethoxazole, C₁₀H₁₁N₃O₃S 7.40 to 8.60% w/v.

Identification A. To a quantity containing 50 mg of Trimethoprim add 30 ml of 0.1M sodium hydroxide and extract with four 50-ml quantities of chloroform . Wash the combined extracts with two 10-ml quantities of 0.1M sodium hydroxide and extract with two 50-ml quantities of chloroform . Wash the combined chloroform extracts with two 10-ml quantities of 0.1M sodium hydroxide and then with 10 ml of water . Shake with 5 g of anhydrous sodium sulphate , filter and evaporate to dryness using a rotary evaporator. The infrared absorption spectrum of the residue, Appendix II A , is concordant with the reference spectrum of trimethoprim .

Acidity pH, 5.0 to 6.5, Appendix V L .

For trimethoprim Extract the chloroform solution reserved in the Assay for sulfamethoxazole with four 50-ml quantities of 1M acetic acid . Wash the combined extracts with 5 ml of chloroform and dilute the aqueous extracts to 250 ml with 1M acetic acid . To 10 ml of this solution add 10 ml of 1M acetic acid and sufficient water to produce 100 ml and measure the absorbance of the resulting solution at the maximum at 271 nm, Appendix II B . Calculate the content of C₁₄H₁₈N₄O₃ taking 204 as the value of A(1%, 1 cm) at the maximum at 271 nm. Using the weight per ml of the oral suspension, calculate the content of C₁₄H₁₈N₄O₃ , weight in volume.

For sulfamethoxazole To 4 g of the oral suspension add 30 ml of 0.1M sodium hydroxide , shake and extract with four 50-ml quantities of chloroform , washing each extract with the same two 10-ml quantities of 0.1M sodium hydroxide . Reserve the combined chloroform extracts for the Assay for trimethoprim. Dilute the combined aqueous solution and washings to 250 ml with water , filter and dilute 5 ml of the filtrate to 200 ml with water (solution A). Carry out the following procedure protected from light using 2 ml of solution A. Add 0.5 ml of 4M hydrochloric acid and 1 ml of a 0.1% w/v solution of sodium nitrite and allow to stand for 2 minutes. Add 1 ml of a 0.5% w/v solution of ammonium sulphamate and allow to stand for 3 minutes. Add 1 ml of a 0.1% w/v solution of N-(1-naphthyl)ethylenediamine dihydrochloride and allow to stand for 10 minutes. Dilute the resulting solution to 25 ml with water and measure the absorbance at 538 nm, Appendix II B , using in the reference cell a solution prepared in the same manner but using 2 ml of water in place of solution A. Dissolve 0.25 g of sulfamethoxazole BPCRS in 50 ml of 0.1M sodium hydroxide and dilute to 250 ml with water . Dilute 5 ml of the resulting solution to 200 ml with water (solution B). Repeat the procedure using 2 ml of solution B and beginning at the words 'Add 0.5 ml of...'. Calculate the content of C₁₀H₁₁N₃O₃ S from the values of the absorbances obtained. Determine the weight per ml of the oral suspension, Appendix V G , and calculate the content of C₁₀H₁₁N₃O₃ S, weight in volume.

Storage Co-trimoxazole Oral Suspension should be protected from light and stored at a temperature not exceeding 30�.

Co-trimoxazole Oral Suspension contains, in 5 ml, 80 mg of Trimethoprim and 400 mg of Sulfamethoxazole.

Reagentia

Ammoniumsulfamaat

N-(1-naphtyl)ethylenediamine

Pharmacy Equivalent Name: Co-trimoxazole Oral Suspension

� Sulfamethoxazole and Trimethoprim Oral Suspension contains not less than 90.0 percent and not more than 110.0 percent of the labeled amounts of sulfamethoxazole (C₁₀H₁₁N₃O₃S) and trimethoprim (C₁₄H₁₈N₄O₃)

Packaging and storage-Preserve in tight, light-resistant containers.

USP Reference standards <11> - USP Trimethoprim RS. USP Sulfamethoxazole RS. USP Sulfamethoxazole N4-glucoside RS. USP SulfanilamideRS. USP Sulfanilic Acid RS.

pH <791>: between 5.0 and 6.5.

Chromatographic purity-

LIMIT OF TRIMETHOPRIM DEGRADATION PRODUCT-

Test preparation-Transfer an accurately measured volume of Oral Suspension, equivalent to about 40 mg of trimethoprim,to a separatory funnel. Extract with three 25-mL portions of a mixture of chloroform and methanol (8:2), collecting the extracts in a 125-mL conical flask. Evaporate the combined extracts to dryness on a steam bath with the aid of a current of air. Dissolve the residue in 2.0 mL of the mixture of chloroform and methanol (8:2), then centrifuge.

Standard preparation A-Dissolve an accurately weighed quantity of USP Trimethoprim RS in a mixture of chloroform and methanol (8:2) to obtain a solution having a known concentration of about 20 mg per mL.

Standard preparation B-Dilute an accurately measured volume of Standard preparation A with a mixture of chloroform and methanol (8:2) to obtain a solution having a known concentration of about 0.1 mg per mL.

Procedure-Apply 5 mL each of the Test preparation. Standard preparation A, and Standard preparation B to separate points on a thin-layer chromatographic plate (see Chromatography <621>) coated with a 0.25-mm layer of chromatographic silica gel. Place the plate in a saturated chromatographic chamber, and develop the chromatogram in a solvent system consisting of a mixture of chloroform, methanol, and ammonium hydroxide (80:20:3) until the solvent front has moved at least 15 cm. Remove the plate from the chamber, air-dry, and view under shortwavelength ultraviolet light: trimethoprim produces a spot at about R_f 0.7, and the trimethoprim degradation product can be seen at R_f 0.3 to 0.5. Any spot from the Test preparation at about R_f. 0.3 to 0.5 is not greater in size and intensity than the spot produced by Standard preparation B at about R_f 0.7, corresponding to not more than 0.5%.

LIMIT OF SULFANILAMIDE, SULFANILIC ACID, AND SULFAMETOXAZOLE, N₄-GLUCOSIDE)-

Alcohol-methanol mixture-Mix dehydrated alcohol and methanol (95:5).

Modified Ehrlich's reagent-Dissolve 100 mg of p-dimethylaminobenzaldehyde in 1 mL of hydrochloric acid, and dilute with alcohol to 100 mL.

Test preparation-Using a syringe, transfer an accurately measured volume of Oral Suspension, equivalent to 200 mg of sulfamethoxazole, to a 100-mL volumetric flask containing 10 mL of ammonium hydroxide, and add 50 mL of methanol. Shake for 3 minutes, and dilute with methanol to volume. Centrifuge a portion of the solution for 3 minutes.

Standard preparation A-Weigh 20 mg of USP Sulfamethoxazole RS into a 10-mL volumetric flask, dissolve in 1 mL of ammonium hydroxide, dilute with methanol to volume, and mix.

Standard preparation B-Weigh 10 mg of USP Sulfanilamide RS into a 50-mL volumetric flask, dissolve in 5 mL of ammonium hydroxide, and dilute with methanol to volume. Pipet 5 mL of this solution into a 100-mL volumetric flask, add 10 mL of ammonium hydroxide, and dilute with methanol to volume.

Standard preparation C-Weigh 10 mg of USP Sulfanilic Acid RS into a 50-mL volumetric flask, dissolve in 5 mL of ammonium hydroxide, and dilute with methanol to volume. Pipet 3 mL of this solution into a 100-mL volumetric flask, add 10 mL of ammonium hydroxide, and dilute with methanol to volume.

Standard preparation D- Weigh 3.0 mg of USP Sulfamethoxazole N4-glucoside RS into a 50-mL volumetric flask, dissolve in 5 mL of ammonium hydroxide, and dilute with methanol to volume.

Procedure-Apply 50 mL each of the Test preparation and Standard preparations A, B, C, and D to separate points on a thin-layer chromatographic plate (see Chromatography <621>) coated with 0.25-mm layer of chromatographic silica gel. Place the plate in an unsaturated chromatographic chamber, and develop the chromatogram in a solvent system consisting of a mixture of Alcohol-methanol mixture, heptane, chloroform, and glacial acetic acid (25:25:25:7) until the solvent front has moved at least 12 cm. Remove the plate from the developing chamber, air-dry, spray with Modified Ehrlich's reagent, and allow the plate to stand for 15 minutes: Any spots from the Test preparation are not greater in size and intensity than spots produced by Standard preparations B, C, and D, respectively, corresponding to not more than 0.5% of sulfanilamide, 0.3% of sulfanilic acid, and 3.0% of sulfamethoxazole N4-glucoside.

Alcohol content. Method II <611>: not more than 0.5% of C2H5OH.

Assay-

Mobile phase-Mix 1400 mL of water, 400 mL of acetonitrile, and 2.0 mL of triethylamine in a 2000-mL volumetric flask. Allow to equilibrate to room temperature, and adjust with 0.2 N sodium hydroxide or dilute glacial acetic acid (1 in 100) to a pH of 5.9 � 0.1. Dilute with water to volume, and Filter through a 0.45-mm membrane, making adjustments if necessary (see System Suitability under Chromatography <621>).

Standard preparation-Dissolve accurately weighed quantities of USP Trimethoprim RS and USP Sulfamethoxazole RS in methanol, and dilute quantitatively with methanol to obtain a solution containing, in each mL, about 0.32 mg and 0.32J mg, respectively, J being the ratio of the labeled amount, in mg, of sulfamethoxazole to the labeled amount, in mg, of trimethoprim in the dosage form. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix to obtain a Standard preparation having known concentrations of about 0.032 mg of USP Trimethoprim RS per mL and 0.032J mg of USP Sulfamethoxazole RS per mL.

Assay preparation-Transfer an accurately measured volume of Oral Suspension, equivalent to about 80 mg of Sulfamethoxazole, to a 50-mL volumetric flask with the aid of about 30 mL of methanol. Sonicate the mixture for about 10 minutes with occasional shaking. Allow to equilibrate to room temperature, dilute with methanol to volume, mix, and centrifuge. Transfer 5.0 mL of the supernatant liquid to a second 50-mL volumetric flask, dilute with Mobile phase to volume, mix, and Filter.

Chromatographic system (see Chromatography <621>)-The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm x 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed under Procedure: the resolution, R, between sulfamethoxazole and trimethoprim is not less than 5.0, and the relative standard deviation for replicate injections is not more than 2.0%. Relative retention times are 1.0 for trimethoprim and 1.8 for sulfamethoxazole.

Procedure-Separately inject equal volumes (about 20 mL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantities, in mg, of trimethoprim (C₁₄H₁₈N₄O₃) and sulfamethoxazole (C₁₀H₁₁N₃O₃S) in each mL of the Oral Suspension taken by the formula:

( 500 C / V ) ( rU / rS ),

in which C is the concentration, in mg per mL, of the appropriate Reference Standard in the Standard preparation, V is the volume, in mL, of Oral Suspension taken, and rU and rS are the responses of the corresponding analyte obtained from the Assay preparation and the Standard preparation, respectively.