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QI have a request for 10% potassium iodide solution. Is that SSKI?
APotassium iodide USP (KI; molecular weight 166.00; CAS number 7681-11-0) occurs as white-to-transparent crystals or as a white granular powder. It is slightly hygroscopic. When dissolved in water, the solution is neutral to slightly alkaline to litmus. Its solubility is as follows: 1 g dissolves in 0.7 mL water, 22 mL ethanol, 2 mL glycerin, and 75 mL acetone at 25̊C. Its dissolution in water is endothermic. A saturated solution of potassium iodide (SSKI) at 25̊C contains 97 to 103 g (approximately 100 g) KI in each 100 mL. Potassium iodide has been used as an expectorant in the treatment of chronic bronchitis, bronchial asthma, and other similar conditions in which thick sputum is produced. Its use as an expectorant is not completely proved, however. Moreover, iodide-induced goiter and hypothyroidism have been reported as side effects in occasional patients. Iodism frequently occurs with KI administration. The salivation, skin eruptions, headaches, gastric irritation, and other symptoms are reversed when the drug is withdrawn.
Potassium iodide oral solution USP contains not less than 94% and not more than 106% of the labeled amount of KI. The USP specifies: "[I]f...solution is not to be used within a short time, add 0.5 mg of sodium thiosulfate for each gram of KI." (Because the monograph is written for a variety of concentrations, this general "rule" applies for various concentrations.) Crystals can form in the solution, especially at refrigerated temperatures.
SSKI is prepared as follows: Dissolve 1000 g (1 kg) KI in 680 mL hot, purified water; allow to cool to about 25̊C; and add sufficient purified water to make 1000 mL (1 L). The resulting solution should be clear, colorless, and odorless and have a very salty taste. Again, if the solution is not to be used soon, add 0.5 g sodium thiosulfate to 1 L SSKI. (Because 1 g = 1000 mg, and the "rule" is 0.5 mg/g KI, then add 0.5 g of sodium thiosulfate per 1000 mL (1 L) of SSKI, which contains 1000 g KI.) (Storage: Protect from light.)
A 10% solution of KI may be compounded by dissolving 10 g KI in approximately 70 mL purified water. Stir, then add sufficient purified water to make 100 mL.
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Mr. Erickson is director of professional affairs at Gallipot Inc.