Final answer:
The hypersensitivity reaction from a drug like penicillin is classified as Type I hypersensitivity, which is immediate and can lead to anaphylaxis, a life-threatening condition.
Step-by-step explanation:
The hypersensitivity reaction that may result from a drug, such as penicillin, is a Type I hypersensitivity. This type of reaction is immediate and can be either localized or systemic. Localized reactions include symptoms like hives and hay fever, while systemic reactions, known as anaphylaxis or anaphylactic shock, can be life-threatening and may involve a dangerous drop in blood pressure and blockage of airways. Type I hypersensitivity involves a primary immune response where IgE antibodies sensitize mast cells; upon subsequent exposure, the cross-linking of IgE on mast cells triggers the release of inflammatory molecules.