Velnacrine (9-amino-1,2,3,4-tetrahydroacridin-1-ol) is an inhibitor of acetylcholinesterase. It was studied for the treatment of Alzheimer's disease however development was discontinued. There has been no research into the use of velnacrine as a cognitive enhancer in the treatment of Alzheimer's disease since 1994. The FDA peripheral and CNS drug advisory board voted unanimously against recommending approval. This review shows the toxic nature of velnacrine, and provides no evidence of efficacy.

Lazabemide is a reversible and selective inhibitor of monoamine oxidase B (MAO-B) that was under clinical development against Parkinson's disease, Alzheimer's disease and as an aid to smoking cessation. The development of the drug was discontinued due to liver toxicity.

Sivelestat is a neutrophil elastase inhibitor approved in Japan and the Republic of Korea for acute lung injury, including acute respiratory distress syndrome in patients with systemic inflammatory response syndrome. Sivelestat is marketed as Elaspol in Japan. Sivelestat competitively inhibited human neutrophil elastase (IC50 = 0.044 uM, Ki = 0.2 uM). It also inhibited leukocyte elastase obtained from rabbit, rat, hamster and mouse.

Benserazide is a peripherally-acting aromatic L-amino acid decarboxylase (AADC) or DOPA decarboxylase inhibitor. Benserazide is only used in conjunction with L-dopa for the treatment of Parkinson's disease under the brand name Madopar in the UK. Madopar HBS (125 mg) is a controlled-release dosage form with 100 mg L-dopa and 25 mg benserazide.

Fosfonet sodium (or phosphonoacetate sodium), an organophosphorus compound, was found to be a specific inhibitor of the virus-induced DNA polymerases and thus could inhibit specifically the replication of herpes-viruses.

Stibogluconic acid (Sodium stibogluconate) is the pentavalent antimonial compound used to treat leishmaniasis and is only available for administration by injection. Sodium stibogluconate is sold in the UK as Pentostam (manufactured by GlaxoSmithKline). Sodium stibogluconate was granted orphan drug designation for the treatment of cutaneous leishmaniasis by the US FDA in January 2007. It is available in the United States only through the Centers for Disease Control. Sodium stibogluconate is indicated for the treatment of various types of a protozoal infection called leishmaniasis, which may result from sandfly bites in tropical and temperate parts of the world. It is also investigated for use/treatment in cancer. The mode of action of sodium stibogluconate is not clearly understood. In vitro exposure of amastigotes to 500 mg pentavalent antimony/ml results in a greater than 50% decrease in parasite DNA, RNA protein and purine nucleoside triphosphate levels. It has been postulated that the reduction in ATP (adenosine triphosphate) and GTP (guanosine triphosphate) synthesis contributes to decreased macromolecular synthesis. Sodium stibogluconate was shown to specifically inhibit type I DNA topoisomerase from Leishmania donovani through the inhibition of the unwinding and cleavage of the supercoiled plasmid pBR322, and to stabilize topoisomerase and DNA covalent complexes but not calf-thymus topoisomerase I and Escherichia coli DNA gyrase. Sodium stibogluconate is also a potent inhibitor of PTPases Src homology PTPase1 (SHP-1), SHP-2, and PTP1B but not the dual-specificity phosphatase mitogen-activated protein kinase phosphatase 1. Sodium stibogluconate combined with IFN-alpha-2b (IFN-α) inhibited solid tumor cell line growth in vitro, in vivo it was well tolerated and augmented cellular immune parameters.

Alrestatin, an inhibitor of aldose reductase, was studied in clinical trials for the treatment of diabetes. But this study was discontinued, because of the high hepatotoxicity events.

Azacosterol (Ornitrol, 20,25-diazacholesterol dihydrochloride, SC 12937) is a cholesterol-lowering drug (hypocholesteremic) which was marketed previously but has since been discontinued. Azacosterol is a sterol derivative of cholesterol with two nitrogen atoms replacing two carbon atoms that acts as a hypocholesteremic agent by blocking delta-24-reductase. Azacosterol has the unintended side effect of causing myotonia. It is an avian contraceptive compound, which reduces fertility by inhibiting cholesterol synthesis. Azacosterol is also useful in the control of rodent populations.

Distigmine is an acetylcholinesterase (AChE) inhibitor. Distigmine shows direct binding to muscarinic receptors in the rat bladder, and repeated oral administration of distigmine causes downregulation of muscarinic receptors in the rat bladder. The observed direct interaction of distigmine with the bladder muscarinic receptors may partly contribute to the therapeutic and/or side effects seen in the treatment of detrusor underactivity. It is usually used to treat myasthenia gravis, dysuria due to hypotonic bladder such as neurogenic bladder or after surgery. Common side effects are: nausea/vomiting, abdominal pain, diarrhea, increased salivation, hypersecretion in respiratory tract, sweating, bradycardia, miosis, difficulty in breathing. Distigmine has a greater risk of causing cholinergic crisis because of accumulation of the drug being more likely than with neostigmine or pyridostigmine and so distigmine is rarely used as a treatment for myasthenia gravis, unlike pyridostigmine and neostigmine.

Clevudine (also known as L-FMAU) is a nucleos(t)ide reverse transcriptase inhibitor, which inhibits the DNA synthesis activity of the hepatitis B virus polymerase. The drug was approved in Korea and Philippines and is being marketed under the names Levovir and Revovir. The drug is indicated in patients with chronic hepatitis B virus infection. Upon administration, clevudine is metabolized to the active metabolite, clevudine triphosphate, which is responsible for the inhibition of viral polymerase.