Angiotensin-converting enzyme inhibitors (ACEI) are commonly prescribed for 
blood pressure control and renal protection. ACEI angioedema is a common problem 
in patients who are taking ACEI, although, in most cases, the disorder is 
self-limited, and spontaneous episodes of apparently unprovoked angioedema stop 
with the discontinuation of the medication. In a subset of patients, 
hospitalization and even intubation are required for airway protection. The 
diagnosis is made clinically. There are no laboratory studies that establish the 
diagnosis. However, such investigations help exclude alternative diagnoses as 
the cause for the patient's presentation. Conventional treatment with regimens 
used to control allergic angioedema is ineffective in this condition. The 
mechanism of ACEI-induced angioedema is thought to be related to its effect on 
the kallikrein-kinin system. Kallikrein is a protease that converts 
high-molecular-weight kininogens into kinins, primarily bradykinin. Medications 
recently developed, primarily icatibant and ecallantide, to control hereditary 
angioedema, a disorder also associated with kallikrein-kinin activation, have 
been used to treat ACEI angioedema with some success. The efficacy of these 
agents and their optimal use remains to be established by randomized and placebo 
controlled trials.