The p-i concept refers to “pharmacological interaction of drugs with immune receptors”. It explains a form of drug hypersensitivity (DH), namely T cell stimulations by drugs, which can lead to various acute inflammatory manifestations (e.g. exanthems, DRESS, SJS/TEN) and late complications in the absence of the eliciting drug (viral reactivations, autoimmunity and multiple drug hypersensitivity (MDH)).
P-i mechanism
Inverse agonist
Enzyme potentiated desensitization
Synaptic pharmacology
Center-surround antagonism
Uncoupling 
Tetanic contraction
Paradoxical reaction