Definitions

An adverse drug reaction (ADR) is defined as any response to a drug that is noxious, unintended, and which occurs at doses normally used in man for the prophylaxis, diagnosis, or therapy of disease (Anon., 1969). These idiosyncratic or ''unexpected'' reactions, which are the focus of this chapter, are to be distinguished from predictable reactions due to overdoses. The problems of case definition and causality assessment of drug-induced liver injury have been addressed by an international group of experts and their recommendations have provided a standardised framework for evaluation of drug-induced hepatotoxicity (Benichou, 1990). When liver biopsy or autopsy has been performed, hepatotoxicity should be classified according to the histology. In the absence of histological data, the term ''liver injury'' has been used to signify abnormalities of the biochemical tests. Liver injury is designated ''hepatocellular'' when there is a twofold (or more) increase in alanine aminotransferase (ALT) alone, or when the ratio of serum activity (activity is expressed as a multiple of upper limit of normal) of ALT to alkaline phosphatase (ALP) is 5 or more. Liver injury is designated ''cholestatic'' when there is a twofold (or more) increase in ALP alone, or when the ratio of serum activity of ALT to ALP is 2 or less. Liver injury is termed ''mixed'' when the ratio of the serum activity of ALT to ALP is between 2 and 5. When increases in the liver tests have been of less than 3 months' duration, the liver injury is considered ''acute'', and when the increase lasted more than 3 months, ''chronic liver injury'' is considered to be present.

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