Metoprine (Standard) is the analytical standard of Metoprine. This product is intended for research and analytical applications. Metoprine (BW 197U) is a potent histamine N-methyltransferase (HMT) inhibitor. Metoprine, a diaminopyrimidine derivative, can cross the blood-brain barrier and increase brain histamine levels by inhibiting HMT[1][2]. Metoprine is an antifolate and antitumor agent[3].