Polymyxin B sulfate is available as a powder in vials containing 500,000 units of polymyxin B.3162; 3163 For intramuscular injection, the 500,000-unit vial should be reconstituted with 2 mL of sterile water for injection, sodium chloride 0.9%, or procaine hydrochloride 1%.3162; 3163 For intravenous infusion, 500,000 units of polymyxin B should be reconstituted by dissolving the drug in 300 to 500 mL of dextrose 5%.3162; 3163 For intrathecal administration, the 500,000-unit vial should be reconstituted with 10 mL of sodium chloride 0.9%.3162; 3163
Units
Each milligram of pure polymyxin base is equivalent to 10,000 units.3162; 3163 Each microgram of pure polymyxin base is equivalent to 10 units.3162; 3163
Polymyxin B sulfate is administered intravenously by continuous infusion, intrathecally, or intramuscularly.3162; 3163 Although polymyxin B sulfate may be administered by intramuscular injection, this route is not recommended due to severe injection site pain, particularly in infants and children.3162; 3163
Intact vials should be stored at controlled room temperature and retained in the carton until time of use to protect from light.3162; 3163 Aqueous solutions of polymyxin B sulfate may be stored under refrigeration for up to 12 months without a significant loss of potency; however, it is recommended that unused, refrigerated portions of the reconstituted solution be discarded after 72 hours.3162; 3163
pH Effects
The pH of maximum stability of polymyxin B is 3.4.2422 In the pH range of 2 to 7, pH has little effect on the rate of decomposition; however, as pH values become more alkaline, solutions are less stable and the rate of decomposition increases markedly.1946; 2422; 3162; 3163
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