AFDX-384 (BIBN-161) is a drug which acts as a selective antagonist of the muscarinic acetylcholine receptors, with selectivity for the M<sub>2</sub> and M<sub>4</sub> subtypes. It is used mainly for mapping the distribution of M<sub>2</sub> and M<sub>4</sub> muscarinic receptors in the brain, and studying their involvement in the development and treatment of dementia and schizophrenia.