Polymyxin B was developed in the 1940s but was infrequently used because of renal toxicity. Since the rise of infections due to multidrug resistant gram-negative organisms, polymyxin B has re-emerged as an important agent. However, its toxicity is still not fully elucidated. In this report, we describe two cases of multiple hypotensive events occurring after polymyxin B administration. Management strategies, such as slowing the infusion rate and administering diphenhydramine, did not mitigate the hypotension. We also describe relatively high polymyxin levels correlated with this effect in one of these cases.