Evaluation of the Physical Compatibility of Intravenous Methocarbamol in Lactated Ringer's, 0.45% Normal Saline, and Plasma-Lyte A.

Background: The need to determine physical compatibility of intravenous admixtures is directly related to patient safety and patient outcomes. While the provision of multi-modal analgesic strategies has increased over the past decade, a paucity of data exists regarding physical compatibility of select medications. Objectives: To evaluate the physical compatibility of methocarbamol in Lactated Ringer's (LR), 0.45% normal saline (0.45% NaCl), and Plasma-Lyte A (PLA) at concentrations of 4, 10, and 20 mg/mL. Methods: Admixtures were prepared and evaluated using previously validated methods under a laminar flow hood using aseptic technique. Samples were prepared in a triplicate manner, 3 mL aliquots were placed into polymethyl methacrylate cuvettes for evaluation at time points 0, 1, 5, 8, and 24 hours. Visual inspection of samples included assignment of a number: 0-no precipitation, 1-trace evidence of precipitation, 2-slight haze, 3-medium haze, and 4-heavy precipitation. Any evidence of precipitation was considered significant. A variable wavelength spectrophotometer set at 547 nanometers was used to measure absorbance. A change in absorbance of ±0.010 was considered significant. A change in pH of ±0.1 was considered significant. Results: No significant changes occurred relating to visual inspection or absorbance across all concentrations and time points for LR; however, there was a significant change in pH across all concentrations at hour 5. In 0.45% NaCl and PLA, no remarkable changes occurred across all concentrations and time points regarding visual observation, spectrophotometric absorbance, and pH analysis. Conclusions: Methocarbamol at concentrations of 4, 10, and 20 mg/mL is physically compatible for up to 1 hour in LR. Methocarbamol is physically compatible in 0.45% NaCl and PLA for up to 24 hours. Chemical stability tests are warranted to confirm these findings.