 an adverse drug reaction (adr) is an injury caused by taking a medication. adrs may occur following a single dose or prolonged administration of a drug or result from the combination of two or more drugs. the meaning of this expression differs from the meaning of "side effect", as this last expression might also imply that the effects can be beneficial. the study of adrs is the concern of the field known as pharmacovigilance. an adverse drug event (ade) refers to any injury occurring at the time a drug is used, whether or not it is identified as a cause of the injury. an adr is a special type of ade in which a causative relationship can be shown. ==classification== adrs may be classified by e.g. cause and severity. ===cause=== *type a: augmented pharmacologic effects - dose dependent and predictable :type a reactions, which constitute approximately 80% of adverse drug reactions, are usually a consequence of the drugâs primary pharmacological effect (e.g. bleeding from warfarin)or a low therapeutic index (e.g. nausea from digoxin), and they are therefore predictable. they are dose-related and usually mild, although they may be serious or even fatal (e.g. intracranial bleeding from warfarin). such reactions are usually due to inappropriate dosage, especially when drug elimination is impaired. the term âside effectsâ is often applied to minor type a reactions. *type b: bizarre effects (or idiosyncratic) - dose independent and unpredictable *type c: chemical effects - biological characteristics can be predicted or rationalised from chemical structure *type d: delayed effects *type e: end-of-treatment 
Drug_safety Pharmacology Pharmacy