Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Opioid receptor agonist; analgesic.
DEFINITION
Pentazocine Injection is a sterile solution in Water for Injections of either Pentazocine Lactate or pentazocine lactate prepared by the interaction of Pentazocine and Lactic Acid.
The injection complies with the requirements stated under Parenteral Preparations and with the following requirements.
Content of pentazocine, C19H27NO
95.0 to 105.0% of the stated amount.
CHARACTERISTICS
A colourless or almost colourless solution.
IDENTIFICATION
A. To a volume containing the equivalent of 90 mg of pentazocine add 5 mL of 0.1M sodium hydroxide and shake the resulting solution with 5 mL of chloroform. Wash the chloroform extract with 2 mL of water, dry over anhydrous sodium sulfate and filter. Evaporate the chloroform using a rotary evaporator and dry the oily residue at a temperature not exceeding 25° at a pressure of 2 kPa for 1 hour. The infrared absorption spectrum of the residue, Appendix II A, is concordant with the reference spectrum of pentazocine (form B) (RS 261).
B. Carry out the method for thin-layer chromatography, Appendix III A, using a silica gel F254 precoated plate (Merck silica gel 60 F254 plates are suitable) and a mixture of 10 volumes of 18M ammonia, 10 volumes of ethyl acetate, 30 volumes of water and 50 volumes of absolute ethanol as the mobile phase but allowing the solvent front to ascend 10 cm above the line of application. Apply separately to the plate 5 µL of each of the following solutions. For solution (1) dilute a quantity of the injection with sufficient methanol to produce a solution containing the equivalent of 0.75% w/v of pentazocine. Solution (2) contains 0.4% w/v of calcium lactate in methanol. After removal of the plate, allow it to dry in air, spray with a 1% w/v solution of potassium permanganate and examine in daylight. The principal spot in the chromatogram obtained with solution (1) is similar in colour, position and size to that in the chromatogram obtained with solution (2).
TESTS
Acidity
pH, 4.0 to 5.0, Appendix V L.
Related substances
Carry out the method for thin-layer chromatography, Appendix III A, using a silica gel F254 precoated plate (Merck silica gel 60 F254 plates are suitable) and a mixture of 3 volumes of methanol, 3 volumes of isopropylamine and 94 volumes of chloroform as the mobile phase. Apply separately to the plate 10 µL of each of the following solutions. For solution (1) dilute a quantity of the injection with sufficient ethanol (96%) to produce a solution containing the equivalent of 2.0% w/v of pentazocine. For solution (2) dilute 1 volume of solution (1) to 100 volumes with ethanol (96%). For solution (3) dilute 1 volume of solution (1) to 200 volumes with ethanol (96%). For solution (4) dilute 1 volume of solution (1) to 400 volumes with ethanol (96%). After removal of the plate, allow it to dry in air and examine under ultraviolet light (254 nm). Heat the plate at 105° for 15 minutes, allow to cool, expose to iodine vapour and re-examine under ultraviolet light (254 nm). By each method of visualisation any secondary spot in the chromatogram obtained with solution (1) is not more intense than the spot in the chromatogram obtained with solution (2) (1%), not more than one such spot is more intense than the spot in the chromatogram obtained with solution (3) (0.5%) and not more than four such spots are more intense than the spot in the chromatogram obtained with solution (4) (0.25%). Disregard any spot remaining on the line of application.
ASSAY
To a quantity containing the equivalent of 0.15 g of pentazocine add sufficient water to produce 100 mL. To 5 mL add 1 mL of 1M hydrochloric acid, dilute to 100 mL with water and measure the absorbance of the resulting solution at the maximum at 278.5 nm, Appendix II B. Calculate the content of C19H27NO taking 69.0 as the value of A(1%, 1 cm) at the maximum at 278.5 nm.
STORAGE
Pentazocine Injection should be protected from light.
LABELLING
The strength is stated in terms of the equivalent amount of pentazocine in a suitable dose-volume.
