Compatibility of acetaminophen with central nervous system medications during simulated Y-site injection

Background
The critical care patient commonly receives a lot of medications including acetaminophen and central nervous system (CNS) agents. However, research on compatibility between acetaminophen and CNS medication is still limited.

Methods
Physical compatibility was evaluated using Y-site simulation by mixing one CNS medication with 10 mg mL-1 of acetaminophen solution under aseptic conditions with a 1 : 1 ratio. The Y-site simulation mixture was subsequently kept in a clean glass tube for incompatibility investigation during 24 hours. The aliquot solutions were visually inspected with bare eyes then additionally with a Tyndall light beam, microscope, and pH at 0, 1, 4, and 24 hours. Medications were considered compatible if there was no visual change (color/gas or turbidity), and no significant particles or precipitates, which referred to United States Pharmacopeia 788 (USP 788), and pH changes less than 0.5 units.

Results
During 24 hours, intravenous acetaminophen was physically compatible with haloperidol, ketamine, midazolam, pethidine, rocuronium and tramadol. Meanwhile, phenytoin, and propofol showed incompatibility with acetaminophen right away. Within four hours, five medications (dexketoprofen, fentanyl, ketorolac, diazepam and phenobarbital) showed incompatibility. Two medications (atropine sulfate and metamizole) were also found to be incompatible with acetaminophen under observation for 24 hours.

Conclusions
Nine of 15 common CNS medications in critical care tested with acetaminophen were physically incompatible for 24 hours.