To the Editor:
I read with interest the recent review of sodium nitroprusside by Friederich et al.  and would like to commend them on their effort. When reading about "Dose and Administration," however, I was disappointed by what I felt were two omissions.
Referencing only the Physicians Desk Reference and without an explanation as to why it should be the case, they stated that "sodium nitroprusside should be mixed only in 5% dextrose in water." Although one would assume this is secondary to concerns regarding the concentration of cyanide in the solution, I can find no article which gives an explanation for this recommendation. In fact, Ikeda et al.  showed that for as long as 72 h after mixing, cyanide concentration was highest in D5W compared with five other solutions, including both normal saline and lactated Ringer's solution. Their conclusion was that "solutions containing electrolytes are preferable to 5% dextrose for the dilution of sodium nitroprusside."
Friederich et al. also stated that "it is important that the solution be protected from light continuously" to prevent release of cyanide, but again Ikeda et al.  exposed sodium nitroprusside to light and compared the cyanide concentration with solutions not exposed to light and found that at 4 h the concentrations were equivalent, and that it was not until 24 h after mixing that the difference in cyanide concentration was statistically higher in the light-exposed solution.
Given that sodium nitroprusside is often infused for less than 4 h in the operating room, and that in most operating suites normal saline or lactated Ringer's solution is more readily available than 5% dextrose, I feel that these two articles could have added some useful information to an otherwise well done review.
Robert M. Jarka, MD
Placerville, CA 95667
1. Friederich JA, Butterworth JF. Sodium nitroprusside: twenty years and counting. Anesth Analg 1995;81:152-62.
2. Ikeda S, Frank PA, Schweiss JF, et al. In vitro cyanide release from sodium nitroprusside in various intravenous solutions. Anesth Analg 1988;67:360-2.
3. Ikeda S, Schweiss JF, Frank PA, et al. In vitro cyanide release from sodium nitroprusside. Anesth Analg 1987;66:381-5.