6/11/15, 2:21Idiosyncratic drug reaction - Wikipedia, the free encyclopedia

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Idiosyncratic drug reactionClassification and external resources

ICD-10 T78.4(http://apps.who.int/classifications/icd10/browse/2015/en#/T78.4)

ICD-9 995.3 (http://www.icd9data.com/getICD9Code.ashx?icd9=995.3)

Idiosyncratic drug reactionFrom Wikipedia, the free encyclopedia

Idiosyncratic drug reactions, alsoknown as type B reactions, are drugreactions that occur rarely andunpredictably amongst the population.This is not to be mistaken with idiopathic,which implies that the cause is notknown. They frequently occur withexposure to new drugs, as they have notbeen fully tested and the full range of possible side-effects have not been discovered; they may also be listed asan adverse drug reaction with a drug, but are extremely rare.

Some patients have multiple-drug intolerance. Patients who have multiple idiopathic effects that are nonspecificare more likely to have anxiety and depression.[1]

Idiosyncratic drug reactions appear to not be concentration dependent. A minimal amount of drug will cause animmune response, but it is suspected that at a low enough concentration, a drug will be less likely to initiate animmune response.

MechanismIn adverse drug reactions involving overdoses, the toxic effect is simply an extension of the pharmacologicaleffect (Type A adverse drug reactions). On the other hand, clinical symptoms of idiosyncratic drug reactions(Type B adverse drug reactions) are different from the pharmacological effect of the drug.

The proposed mechanism of most idiosyncratic drug reactions is immune-mediated toxicity. To create animmune response, a foreign molecule must be present that antibodies can bind to (i.e. the antigen) and cellulardamage must exist. Very often, drugs will not be immunogenic because they are too small to induce immuneresponse. However, a drug can cause an immune response if the drug binds a larger molecule. Some unaltereddrugs, such as penicillin, will bind avidly to proteins. Others must be bioactivated into a toxic compound thatwill in turn bind to proteins. The second criterion of cellular damage can come either from a toxic drug/drugmetabolite, or from an injury or infection. These will sensitize the immune system to the drug and cause aresponse. Idiosyncratic reactions fall conventionally under toxicology.

See alsoIdiosyncrasy

References1. Davies SJ, Jackson PR, Ramsay LE, Ghahramani P (2003). "Drug intolerance due to nonspecific adverse effects related

to psychiatric morbidity in hypertensive patients". Arch. Intern. Med. 163 (5): 592–600. doi:10.1001/archinte.163.5.592

6/11/15, 2:21Idiosyncratic drug reaction - Wikipedia, the free encyclopedia

Page 2 of 2http://en.wikipedia.org/wiki/Idiosyncratic_drug_reaction

(https://dx.doi.org/10.1001%2Farchinte.163.5.592). PMID 12622606 (https://www.ncbi.nlm.nih.gov/pubmed/12622606).

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