Drug eruptions

In medicine, a drug eruption is an adverse drug reaction of the skin. Most drug-induced cutaneous reactions are mild and disappear when the offending drug is withdrawn. These are called "simple" drug eruptions. However, more serious drug eruptions may be associated with organ injury such as liver or kidney damage and are categorized as "complex". Drugs can also cause hair and nail changes, affect the mucous membranes, or cause itching without outward skin changes.
The use of synthetic pharmaceuticals and biopharmaceuticals in medicine has revolutionized human health, allowing us to live longer lives. Consequently, the average human adult is exposed to many drugs over longer treatment periods throughout a lifetime. This unprecedented rise in pharmaceutical use has led to an increasing number of observed adverse drug reactions.
There are two broad categories of adverse drug reactions. Type A reactions are known side effects of a drug that are largely predictable and are called, pharmatoxicologic. Whereas Type B or hypersensitivity reactions, are often immune-mediated and reproducible with repeated exposure to normal dosages of a given drug. Unlike type A reactions, the mechanism of type B or hypersensitivity drug reactions is not fully elucidated. However, there is a complex interplay between a patient's inherited genetics, the pharmacotoxicology of the drug and the immune response that ultimately give rise to the manifestation of a drug eruption.
Because the manifestation of a drug eruption is complex and highly individual, there are many subfields in medicine that are studying this phenomenon. For example, the field of pharmacogenomics aims to prevent the occurrence of severe adverse drug reactions by analyzing a person's inherited genetic risk. As such, there are clinical examples of inherited genetic alleles that are known to predict drug hypersensitivities and for which diagnostic testing is available.