When warfarin reversal must be accomplished rapidly, such as in cases of active bleeding or in preparation for an invasive procedure, multiple options exist, chief among them being fresh frozen plasma (FFP) and four factor prothrombin complex concentrate (4-PCC). Between those two options, the ACCP guidelines suggest (soft recommendation) 4-PCC over FFP. This was based on low level data (very small studies) showing more rapid INR reversal using the former. This study, which came out after publication of the ACCP guidelines, added further weight in favor of 4-PCC in patients deemed appropriate for rapid warfarin reversal in the emergency setting. Though considered low level in that it was a retrospective study, it was larger (around 150 patients in both groups) than prior studies. Despite mounting evidence in favor of 4-PCC some experts (e.g. the authors of this review) remain skeptical as to whether 4-PCC is superior, awaiting information from randomized controlled trials. One such trial has been completed but, as far as I can tell, the results have not been announced. That study, however, enrolled only patients needing urgent warfarin reversal in preparation for an invasive procedure. Though it will shed further light it is unlikely to settle the controversy.
An appeal of 4-PCC is it's rapid acquisition and ease of administration. One of the concerns has been a possible risk of thrombotic complications compared to FFP. That concern was not realized in the retrospective study referenced above.