Previous work describing the compatibility of a mixture of ketamine and propofol in a 50:50 ratio, using a reformulation of the original product containing EDTA, reported that the combination was stable for up to 1 h at room temperature. Another study,12 which used the original formulation (without EDTA), reported the formation of globules after h. The reformulated original brand contains a purified egg phosphatide and EDTA, whereas generic brands contain egg lecithin and no EDTA. The EDTA was added to the formula
tion to address a problem with microbial contamination of the product; however, the effect of EDTA on stability is unknown. The impact of the difference in purity of the emulsifying agent is also unknown. No compatibility or stability data could be found for any other proportions.
The combination of ketamine and propofol remains a milky white opaque emulsion, which makes it difficult to see
the formation of any precipitate. Because of the hydrophobicity of the propofol, a change in the solvent system could cause precipitation of the drug. The pH of the starting solutions differed from the pH of the individual drugs; such a pH shift might cause precipitation. To overcome this visibility problem, other authors have tried dilution,9 centrifugation of the5. Frey K, Sukhani R, Pawlowski J, Pappas AL, Mikat-Stevens AM, Slogoff S. Propofol versus propofol—ketamine for retrobulbar nerve block: comparison of sedation quality, intraocular pressure changes, and recovery profiles.
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