Imidazole in the context of "Nitroimidazole"

Guanine (/ˈɡwɑːniːn/ ) (symbol G or Gua) is one of the four main nucleotide bases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is called guanosine.

With the formula C₅H₅N₅O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with conjugated double bonds. This unsaturated arrangement means the bicyclic molecule is planar.

Purine is a heterocyclic aromatic organic compound that consists of two rings (pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which include substituted purines and their tautomers. They are the most widely occurring nitrogen-containing heterocycles in nature.

Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH₃ form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO form under biological conditions), and an imidazole side chain (which is partially protonated), classifying it as a positively charged amino acid at physiological pH. Initially thought essential only for infants, it has now been shown in longer-term studies to be essential for adults also. It is encoded by the codons CAU and CAC.

Histidine was first isolated by Albrecht Kossel and Sven Gustaf Hedin in 1896. The name stems from its discovery in tissue, from ἱστός histós "tissue". It is also a precursor to histamine, a vital inflammatory agent in immune responses. The acyl radical is histidyl.

Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 1910, histamine has been considered a local hormone (autocoid) because it is produced without involvement of the classic endocrine glands; however, in recent years, histamine has been recognized as a central neurotransmitter. Histamine is involved in the inflammatory response and has a central role as a mediator of itching. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues. It consists of an imidazole ring attached to an ethylamine chain; under physiological conditions, the amino group of the side-chain is protonated.

Ketoconazole, sold under the brand name Nizoral, among others, is an antiandrogen, antifungal, and antiglucocorticoid medication used to treat a number of fungal infections. Applied to the skin it is used for fungal skin infections such as tinea, cutaneous candidiasis, pityriasis versicolor, dandruff, and seborrheic dermatitis. Taken by mouth it is a less preferred option and recommended for only severe infections when other agents cannot be used. Other uses include treatment of excessive male-patterned hair growth in women and Cushing's syndrome.

Common side effects when applied to the skin include redness. Common side effects when taken by mouth include nausea, headache, and liver problems. Liver problems may result in death or the need for a liver transplantation. Other severe side effects when taken orally include QT prolongation, adrenocortical insufficiency, and anaphylaxis. It is an imidazole and works by hindering the production of ergosterol required for the fungal cell membrane, thereby slowing growth.