Oxypurinol is an active metabolite of allopurinol and is an inhibitor of xanthine oxidase. Cardiome Pharma developed oxipurinol for the treatment of allopurinol-intolerant hyperuricemia (gout) and for the treatment of congestive heart failure. It is known, that inhibition of xanthine oxidase can improve myocardial work efficiency by sensitizing cardiac muscle cells to calcium ions, which are a key determinant of cardiac muscle function. However, all these studied were discontinued.

Berythromycin or erythromycin B (also known as 12-deoxyerythromycin A), an acid-stable co-metabolite of the antibiotic erythromycin A, exhibits broad-spectrum antibiotic activity. The antibacterial activity of erythromycin B is similar to that of erythromycin A, but after acid-treatment, resembling exposure to the stomach, erythromycin B substantially retains antibacterial activity, whereas erythromycin A does not. Erythromycin B played an integral part of the structure activity relationship studies of semi-synthetic erythromycins.

Toquizine is an anticholinergic agent. It was used as an antiulcer agent.

Fusaric acid (J-butylpicolinic acid) is a fungal toxin with low to moderate toxicity synthesized by some Fusurium species which cause infections in cereal grains and other agricultural commodities. It may potentiate the effects of other Fusurium toxins. Fusaric acid is a potent inhibitor of DNA synthesis. Fusaric acid has potent anti-proliferative activity in vitro on various normal and cancer cell lines and suggest that it exhibits some cytotoxic specificity for growing and confluent colorectal adenocarcinoma and mammary adenocarcinoma cell lines. Fusaric acid is known as a potent dopamine-beta-hydroxylase inhibitor of high specificity. Fusaric acid calcium salt elicited the hypotensive response primarily through the reduction of total peripheral vascular resistance index.

Urocanic acid is a breakdown (deamination) product of histidine. In the liver, urocanic acid is an intermediate in the conversion of histidine to glutamic acid, whereas in the epidermis, it accumulates and may be both a UV protectant and an immunoregulator. Urocanic acid (UA) exists as a trans isomer (t-UA, approximately 30 mg/cm2) in the uppermost layer of the skin (stratum corneum). t-UA is formed as the cells of the second layer of skin become metabolically inactive. During this process, proteins and membranes degrade, histidine is released, and histidase (histidine ammonia lyase) catalyzes the deamination of histidine to form t-UA. t-UA accumulates in the epidermis until removal by either the monthly skin renewal cycle or sweat. Upon absorption of UV light, the naturally occurring t-UA isomerizes to its cis form, c-UA. Because DNA lesions (e. g. , pyrimidine dimers) in the lower epidermis can result from UV-B absorption, initial research proposed that t-UA acted as a natural sunscreen absorbing UV-B in the stratum corneum before the damaging rays could penetrate into lower epidermal zones. c-UA also suppresses contact hypersensitivity and delayed hypersensitivity, reduces the Langerhans cell count in the epidermis, prolongs skin-graft survival time, and affects natural killer cell activity. It has also been proposed that c-UA may mediate the transient alteration in immune surveillance resulting in immunosuppression induced after UV-irradiation, by interacting with immune cells locally and/or systemically to generate T cells with suppressor function.

Glidazamide is an antidiabetic drug. It is a hypoglycemic agent that is part of the second-generation sulfonamide urea derivatives.

Biologically, methanogens in the colon can use carbon dioxide and hydrogen to produce methane as a by-product. It was previously considered that humans do not utilize methane. However, in a recent study on rodents, results demonstrated that methane could exert anti-inflammatory, anti-oxidant and anti-apoptotic effects. Furthermore, it has bee suggested, that methane-rich saline could be a promising therapeutic agent for clinical treatment of pancreatitis. Methane gas may also be a promising option for the clinical treatment of Acute Lung Injury and Spinal Cord Injury. The exact mechanism underlying the antioxidative, anti-inflammatory, and antiapoptotic activities of methane is not obvious. Different researchers have proposed different hypotheses. Some have hypothesized that methane might accumulate transiently at the interfaces of cell membranes, thereby changing the physicochemical properties or the in-situ functionality of proteins embedded within this environment. Other investigators have suggested that methane could exert effects on membrane channels affecting G-proteins, membrane or receptor-mediated signaling, or acetylcholine-activated ion channel kinetics. It is unknown if mammalian cells contain an oxygenase that is capable of using methane as a substrate, or if the biological effects of methane are caused by the formation of small amounts of the reactive alcohol, methanol, and/or changes in the redox milieu of the cell due to changes in NAD(P)+/NAD(P)H ratio, and whether or not there is a cellular “receptor” for methane. There are also questions remaining around the difference between intraperitoneal vs inhaled administration of methane.

Cyproquinate is an anticoccidial drug, discovered by CIBA in the 1970s. Cyproquinate demonstrated marked anticoccidial activity against E. tenella infected chicks, and against a mixed coccidial infection. Cyproquinate also possessed antimalarial activity, as was demonstrated in a Novartis screen for antimalarial compounds.

Tetrahydrouridine is a potent competitive reversible inhibitor of cytidine deaminase. Tetrahydrouridine can inhibit cell proliferation by regulation of the cell cycle independent of cytidine deaminase (CDA) expression levels. Tetrahydrouridine may be useful for researching potential treatments for high CDA-expressing tumors. Tetrahydrouridine use, alone or in combination with the DNA methyltransferase inhibitor 5-fluoro-2’-deoxycytidine, is being evaluated in animal models and clinical trials for diseases, including cancer and mitochondrial DNA depletion syndrome.