Intravenous (IV) acetaminophen (Ofirmev) is a prime example of how multimodal analgesia can be augmented in the perioperative and ICU settings; however, just as with all things, cost drives availability. Literature has emerged trying to show the cost-effectiveness of IV acetaminophen compared to its oral counterpart, but some of these studies are funded by Mallinckrodt – the pharmaceutical company that manufactures the medication.
The bioavailability and time to maximum plasma concentration are definitely in favor of IV acetaminophen, but does this actually translate to a meaningful difference in analgesic efficacy when compared to oral acetaminophen? Several meta-analyses seem to reach the same conclusion – there’s NO difference.
In general, if my patients are able to tolerate PO, then I’ll give them 1 gram every 6 hours of oral acetaminophen. If they’re in a long surgery or simply not able to keep meds down, I’ll turn to IV acetaminophen and continue the same dosing intervals.
IV acetaminophen can actually cause some degree of hypotension in the critically ill. Although the mechanism isn’t clear, it increases blood flow to the skin (as part of its antipyretic action) thereby shifting blood from the central circulation to the periphery. Furthermore, the IV acetaminophen formulation contains mannitol (an osmotic diuretic) as a stabilizing agent… another potential cause of fluid shifts and hypotension.
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