Final answer:
Exanthematous (morbiliform) drug eruption is the most common type of drug reaction, characterized by a widespread red rash and possibly fever, typically in response to antibiotics.
Step-by-step explanation:
The most common type of drug reaction is exanthematous (morbiliform) drug eruption. This type of reaction is characterized by a widespread red rash that may resemble measles, often accompanied by a fever and other symptoms. This kind of reaction is frequently linked with the use of antibiotics such as penicillins or sulfonamides. Contact dermatitis, such as the type caused by poison ivy, is an example of a Type IV hypersensitivity reaction, where the immune system responds to small molecules that have bound to proteins in the skin. In contrast to exanthematous drug eruptions, Type IV hypersensitivities involve T-cell-mediated immune responses that lead to inflammation and are not the most common type of drug reaction.