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.

Myfadol is a phenacylpiperidine derivative patented by Tanabe Seiyaku Co., Ltd as low molecular weight non-peptide analgesic. Myfadol produces hot-plate analgesia in rodents with minimal side-effects, and when given parenterally in humans produces analgesia to experimentally-produced and postoperative pain.

AZD9056 was developed as a selective inhibitor of the purinergic receptor P2X7, a key player in the generation and secretion of several proinflammatory cytokines. AZD 9056 participated is phase II clinical trials for osteoarthritis, inflammatory bowel disease, and chronic obstructive pulmonary disease but these studies were discontinued in 2009 because the drug failed to show significant efficacy in trials. In addition, in 2015 AZD 9056 was studied for the treatment of Crohn's disease (CD), although the drug has shown a beneficial risk profile the lack in the change of inflammatory biomarkers questions its anti-inflammatory potential.

Butobendine is trihydroxybenzoic acid derivative with marked antiarrhythmic activities in rats and cats.

Norbuprenorphine is a major metabolite of buprenorphine and potent agonist of μ, δ, and κ opioid receptors. Norbuprenorphine is the only known active metabolite of buprenorphine. It has been shown to be a respiratory depressant in rats, but only at concentrations at least 50-fold greater than those observed following application to humans of BuTrans 20 mcg/h. Compared with buprenorphine, norbuprenorphine causes minimal antinociception but greater respiratory depression. In rats, nor-buprenorphine had 1/50th the analgesic potency of buprenor-phine but 10-fold greater respiratory depressant potency. Norbuprenorphine is an in vitro substrate of the efflux transporter P-glycoprotein (Mdr1). Norbuprenorphine is an in vitro and in vivo substrate of P-glycoprotein. P-glycoprotein-mediated efflux influences brain access and antinociceptive, but not the respiratory, effects of norbuprenorphine.