C olistin (polymyxin E) is a cationic polypeptide antibi- otic that exerts its bactericidal activity through a deter- gent-like mechanism, interfering with the structure and function of the bacterial outer cytoplasmic membrane re- sulting in bacterial death. 1 In vitro, colistin has shown ex- cellent activity against many gram-negative aerobic bacilli, including those resistant to conventional antimicrobial agents, although it has little activity against Serratia spp., Proteus mirabilis, and non-aeruginosa species of Pseu- domonas. 2,3 Moreover, in vitro resistance of Pseudomonas aeruginosa to colistin is extremely rare, which has allowed its use in long-term suppressive treatment of patients chronically infected by this organism. 4,5 Recently, nonsys- temic administration of aerosolized colistin has been used successfully to manage cystic fibrosis and nosocomial res- piratory infections. 4,6 Studies have shown that administra- tion of aerosolized colistin is safe and devoid of adverse effects that have been observed when it is administered in- travenously. 5,7 We report a case of a critically ill patient with nosocomial pneumonia who developed hypotensive episodes during treatment with aerosolized colistin. Case Report A 62-year-old Arab male was transferred (January 2005) to the inten- sive care unit (ICU) due to respiratory failure secondary to recurrent atelec- tasis of the left lung and septic shock. Nineteen years ago, at the age of 44 years, the patient had been admitted to King Faisal Specialist Hospital and Research Center after a motor vehicle accident that left him quadriplegic. Since that time, he had been a long-term patient at this hospital. His back- ground history also included type 2 diabetes mellitus and depression. During his prolonged hospital stay, the patient had been colonized with different multidrug-resistant P. aeruginosa species that acted as a reservoir for his infections. He had safely received different antibiotics, including colistin, ciprofloxacin, clindamycin, and trimethoprim/sul- Hypotension Following Treatment with Aerosolized Colistin in a Patient with Multidrug-Resistant Pseudomonas aeruginosa Hakeam A Hakeam and Abdullah M Almohaizeie Author information provided at the end of the text. OBJECTIVE: To report a case of a man who developed temporary hypotension after aerosolized colistin administration. CASE SUMMARY: A 62-year-old Arab male was admitted to the intensive care unit for respiratory failure and septic shock. Simultaneous therapy using intravenous and aerosolized colistin was initiated for the management of multidrug-resistant Pseudomonas aeruginosa. A significant but transient drop in blood pressure occurred when aerosolized colistin was introduced. However, when it was stopped, but intravenous administration was continued, no hypotension was observed. Moreover, the combined use of aerosolized amikacin with intravenous colistin did not significantly affect blood pressure. DISCUSSION: It is widely accepted that aerosolization allows safe administration of colistin in the absence of significant systemic adverse effects. However, in our patient, hypotension was observed with aerosolized colistin, but not with the systemic formulation. The lack of adverse effects with administration of aerosolized amikacin in this patient demonstrates the safety of the aerosolization technique. Use of the Naranjo scale indicated a probable relationship between hypotension and aerosolized colistin administration. CONCLUSIONS: This case suggests that hypotension may be induced with administration of aerosolized colistin. Although this effect is rare, clinicians should be aware that hypotension may develop in critically ill patients following aerosolized colistin treatment. KEY WORDS: aerosolized, amikacin, colistin, hypotension, polymyxin. Ann Pharmacother 2006;40:1677-80. Published Online, 8 Aug 2006, www.theannals.com, DOI 10.1345/aph.1H019 The Annals of Pharmacotherapy ■ 2006 September, Volume 40 ■ 1677 www.theannals.com