NIMBEX (cisatracurium besylate) is a nondepolarizing skeletal muscle relaxant for intravenous administration. Compared to other neuromuscular blocking agents, it is intermediate in its onset and duration of action. Cisatracurium besylate is one of 10 isomers of atracurium besylate and constitutes approximately 15% of that mixture. Cisatracurium besylate is [1R- [1α,2α(1' R*,2'R*)]]-2,2'-[1,5-pentanediylbis[oxy(3-oxo-3,1-propanediyl)]]bis[1-[(3,4-dimethoxyphenyl)methyl]-1,2,3,4- tetrahydro-6,7-dimethoxy-2-methylisoquinolinium] dibenzenesulfonate. The molecular formula of the cisatracurium parent biscation is C₅₃H₇₂N₂O₁₂ and the molecular weight is 929.2. The molecular formula of cisatracurium as the besylate salt is C₆₅H₈₂N₂O₁₈S₂ and the molecular weight is 1243.50. The structural formula of cisatracurium besylate is:

The log of the partition coefficient of cisatracurium besylate is -2.12 in a 1-octanol/distilled water system at 25°C.

NIMBEX Injection is a sterile, non-pyrogenic aqueous solution provided in 5 mL, 10 mL, and 20 mL vials. The pH is adjusted to 3.25 to 3.65 with benzenesulfonic acid. The 5 mL and 10 mL vials each contain cisatracurium besylate, equivalent to 2 mg/mL cisatracurium. The 20 mL vial, intended for ICU use only, contains cisatracurium besylate, equivalent to 10 mg/mL cisatracurium. The 10 mL vial, intended for multiple-dose use, contains 0.9% benzyl alcohol as a preservative. The 5 mL and 20 mL vials are single-use vials and do not contain benzyl alcohol.

Cisatracurium besylate slowly loses potency with time at a rate of approximately 5% per year under refrigeration (5°C). NIMBEX should be refrigerated at 2° to 8°C (36° to 46°F) in the carton to preserve potency. The rate of loss in potency increases to approximately 5% per month at 25°C (77°F). Upon removal from refrigeration to room temperature storage conditions (25°C/77°F), use NIMBEX within 21 days, even if rerefrigerated.

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