MK-0686 is a bradykinin B1 receptor antagonist patented by American multinational pharmaceutical company Merck & Co for the treatment of neuropathic pain and inflammation. MK-0686 demonstrates significantly reduced susceptibility to human P-gp mediated efflux and shows good potential for human CNS penetration based on brain levels in CF-1 mice and monkeys. Additionally, MK-0686 also exhibited good CNS bradykinin B1 receptor occupancy in the transgenic rat expressing the human B1 receptor and showed oral efficacy in reducing CFA-induced hyperalgesia in a humanized mouse. Unfortunately, in phase II clinical trials MK-0686 failed to demonstrate efficacy in phase II clinical trials.

Telinavir (previously known as SC-52151) was developed as an anti-HIV aspartyl protease inhibitor for the treatment of HIV Infections. Telinavir participated in Phase I/II clinical study. In spite of the drug was well tolerated no antiviral activity was produced and further development of the drug was discontinued.

Levomequitazine is the L-enantiomer of mequitazine. The antihistaminergic activity mainly resides in the S-enantiomer, L-mequitazine, whereas the anticholinergic activity mainly resides in the D-enantiomer. It was shown, that L-enantiomer of mequitazine is less potent antagonist of human M3 muscarinic acetylcholine receptors than D-enantiomer. In vitro binding studies have shown that the affinity of L-mequitazine for H1 receptors is approximately ten times higher and to muscarinic receptors ten times lower, compared to d-mequitazine. Memory impairment was observed after administration of L-mequitazine 10 mg alone on delayed recall. This could be due to indirect effects of H1 receptor blockade. L-mequitazine 10 mg produced mild driving impairment, whereas L-mequitazine 2.5 and 5.0 mg show no effects on driving. Levomequitazine had been in phase III clinical trials by Pierre Fabre for the treatment of perennial allergic rhinitis and seasonal allergic rhinitis.