Type A (Augmented) reactions will occur in everyone if enough of the drug is given because they are due to excess of normal, predictable, dose-related, pharmacodynamic effects. They are common and skilled management reduces their incidence, e.g. postural hypotension, hypoglycaemia, hypokalemia.
Type B (Bizarre) reactions will occur only in some people. They are not part of the normal pharmacology of the drug, are not dose-related and are due to unusual attributes of the patient interacting with the drug. These effects are predictable where the mechanism is known (though predictive tests may be expensive or impracticable), otherwise they are unpredictable for the individual, although the incidence may be known. The class includes unwanted effects due to inherited abnormalities (idiosyncrasy) (see Pharmacogenetics) and immunological processes (see Drug allergy). These account for most drug fatalities.
Type D (Delayed) effects following prolonged exposure, e.g. carcinogenesis or short-term exposure at a critical time, e.g. teratogenesis.
Type E (Ending of use) reactions, where discontinuation of chronic therapy is too abrupt, e.g. of adrenal steroid causing rebound adrenocortical insufficiency, of opioid causing the withdrawal syndrome.
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