Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Dihydrofolate reductase inhibitor + sulfonamide antibacterial.
DEFINITION
Co-trimazine Injection is a sterile suspension in Water for Injections containing Trimethoprim and Sulfadiazine in the proportion one part to five parts.
PRODUCTION
Co-trimazine Injection is prepared by the addition, with aseptic precautions, of sterile Trimethoprim to a solution of sulfadiazine sodium previously sterilised by filtration. The solution of sulfadiazine sodium is prepared by the interaction of Sulfadiazine and Sodium Hydroxide.
The injection complies with the requirements stated under Parenteral Preparations and with the following requirements.
Content of trimethoprim, C14H18N4O3
90.0 to 110.0% of the stated amount.
Content of sulfadiazine, C10H10N4O2S
90.0 to 110.0% of the stated amount.
CHARACTERISTICS
A suspension of an almost white solid in a pale straw-coloured solution.
IDENTIFICATION
A. The light absorption, Appendix II B, in the range 250 to 325 nm of the solution obtained in the Assay for trimethoprim exhibits a maximum only at 271 nm.
B. Carry out the method for thin-layer chromatography, Appendix III A, using the following solutions.
(1) Ensure that the injection is homogeneous by gently inverting the container several times. To 2.5 mL of the well mixed injection add 4 mL of hydrochloric acid and dilute to 50 mL with 1.4M methanolic ammonia.
(2) 2.0% w/v of sulfadiazine BPCRS in 1.4M methanolic ammonia.
(3) 0.4% w/v of trimethoprim BPCRS in 1.4M methanolic ammonia.
CHROMATOGRAPHIC CONDITIONS
(a) Use as the coating silica gel F254.
(b) Use the mobile phase as described below.
(c) Apply 1 µL of each solution.
(d) Develop the plate to 15 cm.
(e) After removal of the plate, dry in air and examine under ultraviolet light (254 nm).
MOBILE PHASE
5 volumes of water, 15 volumes of dimethylformamide and 75 volumes of ethyl acetate.
CONFIRMATION
In the chromatogram obtained with solution (1):
one of the principal spots in the chromatogram obtained with solution (1) corresponds to the principal spot in the chromatogram obtained with solution (2);
the other principal spot corresponds to the principal spot in the chromatogram obtained with solution (3).
C. To 5 mL of the filtrate obtained in the Assay for sulfadiazine add 10 mL of water and 5 mL of thiobarbituric acid-citrate buffer, mix and heat on a water bath for 30 minutes. A pink colour is produced.
Alkalinity
pH, 10.0 to 10.5, Appendix V L.
ASSAY
For trimethoprim
Extract the chloroform solution reserved in the Assay for sulfadiazine with three quantities, of 100, 50 and 50 mL, of 1M acetic acid and dilute the combined extracts to 500 mL with 1M acetic acid. To 5 mL add 35 mL of 1M acetic acid and sufficient water to produce 200 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.
For sulfadiazine
Disperse the trimethoprim evenly throughout the injection by gently inverting the container several times, avoiding the formation of foam. Transfer a quantity of the injection containing the equivalent of 2 g of Sulfadiazine to a separating funnel containing 50 mL of 0.1M sodium hydroxide and extract with two quantities, of 100 mL and 50 mL, of chloroform, washing the extract with the same 25 mL quantity of 0.1M sodium hydroxide. Reserve the combined chloroform extracts for the Assay for trimethoprim.
Dilute the combined aqueous solutions and washings to 250 mL with water, filter and dilute 5 mL of the filtrate to 200 mL with water. Dilute 10 mL of this solution to 100 mL with water. To 3 mL of the resulting solution add 1 mL of 2M 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 sulfamate and allow to stand for 3 minutes. Add 1 mL of a 0.1% w/v solution of N-(1-naphthyl)ethylenediamine dihydrochloride, allow to stand for 10 minutes, add sufficient water to produce 25 mL and measure the absorbance of the resulting solution at 538 nm, Appendix II B. Repeat the operation using 3 mL of a solution prepared by dissolving 0.2 g of sulfadiazine BPCRS in 50 mL of 0.1M sodium hydroxide, adding sufficient water to produce 200 mL, diluting 5.0 mL of the resulting solution to 250 mL with water and beginning at the words ‘add 1 mL of 2M hydrochloric acid…’. Calculate the content of C10H10N4O2S in the injection from the absorbances obtained using the declared content of C10H10N4O2S in sulfadiazine BPCRS.
When trimethoprim and sulfadiazine injection is prescribed or demanded, Co-trimazine Injection shall be dispensed or supplied.
