Một phản ứng với một chất mà một cá nhân đã được nhạy cảm thông qua sự hình thành của một kháng thể IgE cụ thể. Nó được đặc trưng bởi việc phát hành chất vasoactive và sự hiện diện của triệu chứng toàn thân. | 90 Section 3 Pharmacological principles Anaphylactic reaction A response to a substance to which an individual has been previously sensitized via the formation of a specific IgE antibody. It is characterized by the release of vasoactive substances and the presence of systemic symptoms. Anaphylactoid reactions A response to a substance that is not mediated by a specific IgE antibody but is characterized by the same release of vasoactive substances and presence of systemic symptoms as an anaphylactic reaction. Section 4 Pharmacodynamics Drug-receptor interaction A basic understanding of the interaction between drugs and receptors underlies much of what is covered in the examinations. Ligand A ligand is a chemical messenger able to bind to a receptor. May be endogenous or exogenous drugs . Receptor A receptor is a component of a cell that interacts selectively with a compound to initiate the biochemical change or cascade that produces the effects of the compound D R DR where D is drug R is receptor and DR is drug-receptor complex. It is assumed that the magnitude of the response is proportional to the concentration of DR . DR . Law of mass action The rate of a reaction is proportional to the concentration of the reacting components. Kf D R DR Kb where Kf is the rate of forward reaction and Kb is the rate of backward reaction. At equilibrium the rates of the forward and back reactions will be the same and the equation can be rearranged Kf D R Kb DR 92 Section 4 Pharmacodynamics The affinity constant The affinity constant measured in l mmol has the symbol KA where Ka Kf Kb and it reflects the strength of drug-receptor binding The dissociation constant The dissociation constant measured in mmol l has the symbol KD where Kd Kb Kf and it reflects the tendency for the drug-receptor complex to split into its component drug and receptor. Often KD is described differently given that the law of mass action states that at equilibrium Kf D R Kb DR or Kb Kf D R DR so D R Kd pR
