NUBAIN (nalbuphine hydrochloride)    is  a synthetic agonist-antagonist of the phenanthrene series. It is  chemically related to both the widely used opioid , , and the potent  opioid analgesic, oxymorphone. Chemically nalbuphine hydrochloride is  17-(cyclobutylmethyl)-4,5α-epoxymorphinan-3,6α,14-triol hydrochloride.  Nalbuphine hydrochloride molecular weight is 393.91 and is soluble in H2O (35.5 mg/mL @ 25ºC) and ethanol (0.8%); insoluble in CHCl3 and ether. Nalbuphine hydrochloride has pKa values of 8.71 and 9.96. The molecular formula is C21H27NO4·HCl.  NUBAIN  is a sterile solution suitable for subcutaneous, intramuscular, or  intravenous injection. NUBAIN is available in two concentrations, 10 mg  and 20 mg of nalbuphine hydrochloride per mL. Both strengths in 10 mL  vials contain 0.94% sodium citrate hydrous, 1.26% citric acid anhydrous,  and 0.2% of a 9:1 mixture of methylparaben and propylparaben as  preservatives; pH is adjusted, if necessary, to 3.5 to 3.7 with  hydrochloric acid. The 10 mg/mL strength contains 0.2% sodium chloride. NUBAIN  is also available in ampuls in a sterile, paraben-free formulation in  two concentrations, 10 mg and 20 mg of nalbuphine hydrochloride per mL.  One mL of each strength contains 0.94% sodium citrate hydrous, and 1.26%  citric acid anhydrous; pH is adjusted, if necessary, to 3.5 to 3.7 with  hydrochloric acid. The 10 mg/mL strength contains 0.2% sodium chloride.