Otenzepad is the first competitive muscarinic M2 antagonist that is cardioselective and had been in phase III clinical trials for the treatment of arrhythmias and bradycardia. Otenzepad was originally developed by Boehringer Ingelheim Pharma KG (Boehringer Ingelheim) in Germany. The parent company is developing oral and IV formulations of the drug for use in symptomatic bradycardia, sinus bradycardia, sick sinus syndrome and symptomatic arrhythmias after intoxication. However, all these research has been discontinued. Otenzepad binds to muscarinic cholinergic receptors in a simple competitive manner. Its affinity for cardiac (M2) muscarinic receptors is about 7 times greater than for ganglionic (M1) receptors and about 36 times greater than for glandular (M3) receptors. The (+)-enantiomer of otenzepad is about 8 times more potent at M2-receptors than the (−)-enantiomer. In a double-blind study, 48 healthy male volunteers were randomised to single oral doses of placebo or otenzepad (120, 240 or 480mg). Heart-rate (HR) was significantly increased by the 250 and 480mg doses (by 15 and 21 beats/minute, respectively). The 480mg dose also increased Diastolic Blood Pressure (DBP) significantly compared with placebo. The oral pharmacokinetics of otenzepad were investigated in a double-blind study in which 48 healthy male volunteers were randomised to single oral doses of placebo or otenzepad (120, 240 or 480mg). Otenzepad bioavailability was 45%, mean residence time (MRT) was 12.5 hours and tmax occurred 2.5 hours postdose.