Imidazole is a heterocyclic aromatic organic compound. It is further classified as an alkaloid. Imidazole refers to the parent compound C3H4N2, while imidazoles are a class of heterocycles with similar ring structure but varying substituents. This ring system is present in important biological building blocks such as histidine, and the related hormone histamine. Imidazole can act as a base and as a weak acid. Imidazole exists in two tautomeric forms with the hydrogen atom moving between the two nitrogens. Many drugs contain an imidazole ring, such as antifungal drugs and nitroimidazole.