An adverse drug reaction (ADR) may be defined as ‘an appreciably harmful or unpleasant reaction, resulting from an intervention related to the use of a medicinal product.
Mechanisms of
Adverse Drug Reactions
An
adverse drug reaction (ADR) may be
defined as ‘an appreciably harmful or unpleasant reaction, resulting from an
intervention related to the use of a medicinal product, which predicts hazard
from future administration and warrants prevention or specific treatment, or
alteration of the dosage regimen, or with-drawal of the product’ (Edwards and
Aronson, 2000). This has to be contrasted with the term adverse drug event, which
refers to untoward occurrences follow-ing drug exposure but not necessarily
caused by the medicine (Asscher, Parr and Whitmarsh, 1995). This chapter
focuses on ADRs rather than adverse drug events.
Although
the drug discovery process has been revolutionised by new techniques such as
combinatorial chemistry and high-throughput screening, drug safety assessment
lags well behind and is still reliant on many of same technologies that have
been used for several decades. By the time a drug is marketed, only about
1500–3000 patients may have been exposed to the drug (Asscher, Parr and
Whitmarsh, 1995; Rawlins, 1995). Thus, only those adverse reactions occurring
at a frequency of greater than 1 in 500–1000 will have been identified at the
time of licensing. Assessment of ADRs therefore is likely to represent an
important aspect of drug therapy for many years to come, and indeed, with the
development of new biotechnology compounds, it is likely that the pattern of
these reactions will change. Furthermore, using gene and protein screening
technologies, many new targets will be discovered. As new drugs are devel-oped
to modulate the function of these targets, it is very unlikely that we will
fully understand the biol-ogy of the new target molecule(s), and this will lead
to unforeseen adverse reactions. For example, adverse effects such as the
exacerbation of multiple sclero-sis, systemic lupus erythematosus (SLE) and
blood dyscrasias that have been reported with anti-tumour necrosis factor
(anti-TNF) therapies (Furst et al.,
2000; Sharief and Hentges, 1991) or cardiovascular events with
cyclo-oxygenase-II (COX-II) inhibitors (Fries et al., 2006) may not have been reasonably expected given the known pharmacology of these therapies.
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