Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Barbiturate.
DEFINITION
Pentobarbital Injection is a sterile1 solution of Pentobarbital Sodium in a suitable vehicle.
The injection complies with the requirements stated under Parenteral Preparations and with the following requirements.
Content of pentobarbital sodium, C11H17N2NaO3
95.0 to 105.0% of the stated amount.
CHARACTERISTICS
A clear, colourless or almost colourless solution.
IDENTIFICATION
A. The infrared absorption spectrum of the residue obtained in the Assay, Appendix II A, is concordant with the reference spectrum of pentobarbital (RSV 34).
B. Melting point of the residue obtained in the Assay, about 128°, Appendix V A.
C. When introduced on a platinum wire into the flame of a Bunsen burner, imparts a yellow colour to the flame.
TESTS
Alkalinity
pH, 10.0 to 11.5, Appendix V L.
Isomer
To a volume containing 0.3 g of Pentobarbital Sodium diluted, if necessary, to 5 mL with water, add 0.3 g of 4-nitrobenzyl bromide dissolved in 10 mL of ethanol (96%) and heat under a reflux condenser for 30 minutes. Cool to 25°, filter, wash the residue with four 5 mL quantities of water and transfer as completely as possible to a small flask. Add 25 mL of ethanol (96%) and heat under a reflux condenser for 10 minutes. The residue, after drying at 105° for 30 minutes, melts completely between 136° and 155°.
ASSAY
To a volume containing 0.5 g of Pentobarbital Sodium diluted to 15 mL with water add 5 mL of 2M hydrochloric acid, extract with 50 mL of ether and then with successive 25 mL quantities of ether until complete extraction is effected. Wash the combined extracts with two 5 mL quantities of water and wash the combined aqueous washings with 10 mL of ether. Add the ether to the main ether extract, evaporate to low volume, add 2 mL of absolute ethanol, evaporate to dryness and dry the residue to constant weight at 105°. Each g of residue is equivalent to 1.097 g of C11H17N2NaO3.
When pentobarbitone injection is prescribed or demanded, Pentobarbital Injection shall be dispensed or supplied.
1 Solutions containing 20% w/v of Pentobarbital Sodium in 100 mL and 500 mL quantities are also available for purposes other than injection; such solutions are not necessarily sterile but comply with all the other requirements of the monograph; they may be coloured.
