Stability and Compatibility of an Intramuscular Fetal Anesthetic Cocktail for Fetal Intervention

The aim of the study was to evaluate chemical stability and physical compatibility when combining fentanyl, rocuronium, and atropine in a fixed ratio to support intramuscular drug delivery during fetal intervention and surgery.

A highly concentrated combination of fentanyl, rocuronium, and atropine was created based on common prescribing practices at a maternal-fetal care center. Chemical stability testing was completed using liquid chromatograph mass spectrometry-mass spectrometry (LC/MS-MS) to detect and quantitate atropine, rocuronium, and fentanyl, with fentanyl-d5 being an internal standard at 6, 12, 24, and 36 h following sample preparation. Physical compatibility testing was completed using United States Pharmacopeia (USP) <788> recommended analytical technique of light obscuration in addition to novel backgrounded membrane imaging at 6 and 24 h following sample preparation. Physical compatibility was determined using USP <788> particle count limits for both techniques.

Based on LC/MS-MS results, the samples retained expected medication concentrations at all time points tested. For physical compatibility testing, the particle counts met criteria to be considered compatible per USP <788> large-volume particle count thresholds at 6 h by both methods but exceeded tolerable thresholds at 24 h.

The combination of rocuronium, fentanyl, and atropine for intramuscular fetal administration is physically compatible and chemically stable for 6 h.