Lack of regulation of the classical complement pathway through the deficiency in C1-inhibitor results in episodic angioedema. C1-inhibitor defiency can be hereditary or acquired, resulting in hereditary or acquired angioedema. C1-inhibitor plays the role of inactivating C1r and C1s to prevent further downstream classical complement activity. C1-inhibitor controls the processes involved in maintaining vascular permeability. As a result, C1-inhibitor levels of less than 50% of the standard lead to increased vascular permeability, characteristic of angioedema. Cinryze, a human plasma derived C1-esterase inhibitor, has been approved for use in 2008 for the prevention of hereditary angioedema attacks.