Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Adrenoceptor agonist.
DEFINITION
Metaraminol Injection is a sterile solution of Metaraminol Tartrate in Water for Injections.
The injection complies with the requirements stated under Parenteral Preparations and with the following requirements.
Content of metaraminol, C9H13NO2
90.0 to 110.0% of the stated amount.
IDENTIFICATION
A. In the test for Related substances, the principal spot in the chromatogram obtained with solution (2) corresponds to that in the chromatogram obtained with solution (5).
B. Dilute a volume containing the equivalent of 5 mg of metaraminol to 10 mL with water and extract with four 15 mL quantities of chloroform. To 0.5 mL of the aqueous layer add 0.5 mL of phosphomolybdotungstic reagent and 5 mL of dilute sodium carbonate solution and allow to stand for 5 minutes. An intense blue colour is produced.
C. To 4 mL of the aqueous layer obtained in test B add 5 mL of borate buffer pH 9.6 and 1 mL of a freshly prepared 0.5% w/v solution of sodium 1,2-naphthoquinone-4-sulfonate and allow to stand for 1 minute. Add 0.2 mL of a 2% v/v solution of benzalkonium chloride solution and 5 mL of toluene and shake. A mauve colour is produced immediately in the toluene layer (distinction from phenylephrine).
TESTS
Acidity
pH, 3.2 to 4.5, Appendix V L.
Related substances
Carry out in subdued light the method for thin-layer chromatography, Appendix III A, using a silica gel precoated plate (Merck silica gel 60 plates are suitable) and a mixture of 10 volumes of 13.5M ammonia, 80 volumes of chloroform and 80 volumes of methanol as the mobile phase. Apply separately to the plate 10 µL of each of the following solutions. For solution (1) evaporate a volume of the injection containing the equivalent of 20 mg of metaraminol to dryness, dissolve the residue as completely as possible in 2 mL of methanol and filter. For solution (2) dilute 1 volume of solution (1) to 20 volumes with methanol. For solution (3) dilute 1 volume of solution (1) to 100 volumes with methanol. Solution (4) contains 0.1% w/v of methyl 4-hydroxybenzoate in methanol. Solution (5) contains 0.050% w/v of metaraminol tartrate BPCRS in methanol. After removal of the plate, allow it to dry in air and spray with a solution prepared in the following manner. Mix 25 mL of a 0.45% w/v solution of sulfanilic acid in 1M hydrochloric acid with 1.5 mL of a 5% w/v solution of sodium nitrite, allow to stand for 5 minutes and mix cautiously with 25 mL of 2M sodium carbonate. Any secondary spot in the chromatogram obtained with solution (1), other than any spot corresponding to methyl 4-hydroxybenzoate, is not more intense than the spot in the chromatogram obtained with solution (3) (1%).
ASSAY
To a quantity containing the equivalent of 10 mg of metaraminol add sufficient water to produce 200 mL. Wash 25 mL with four 25 mL quantities of chloroform, discard the washings and filter the aqueous solution. Measure the absorbance of the filtrate at the maximum at 272 nm, Appendix II B. Calculate the content of C9H13NO2 taking 111 as the value of A(1%, 1 cm) at the maximum at 272 nm.
STORAGE
Metaraminol Injection should be protected from light.
LABELLING
The strength is stated in terms of the equivalent amount of metaraminol in a suitable dose-volume.
