Inorganic drugs may be divided into three different categories (Table 10.2):
1. Active complexes. Here, the entire complex, metal ion, and ligands, determines the action. Many coordination compounds act as neurotoxins by blocking acetylcholine receptors. Cisplatin and other uncharged Pt(II) and Ru(II) complexes are active as antitumor drugs (Section 10.6.4) and Bi(III) complexes are used in the treatment of gastrointestinal diseases (Section 10.6.7). Insoluble salts of certain heavy metals can be applied as x-ray contrast compounds, such as BaSO4. The rare earth gadolinium is used in NMR diagnostics. Tin coordinated to protophorphyrin inhibits heme oxygenase degradation of a certain iron-heme product to bilirubin. The latter compound is the most frequent cause of neonatal jaundice.
2. Active elements. Here, the metal ion is decisive for the action of the drug while the anion or ligand only serves to keep the metal ion in solution or simply as a counter ion. The effect of lithium in the manic-depressive psychosis is well known although not fully understood. Interestingly, the lithium ion is counteracting both phases of the cyclic course of this disease (Section 10.6.1). The cariostatic effect of fluoride is well established although the mechanism is still unclear. Silver(I) and mercury(II) are potential antibacterial agents, and silver sulfadiazine is used clinically (Section 10.6.5). Technetium (the 99mTc isotope) is applied in radiodiagnostics, administered as a TcVII(CNR)+ complex. The significance of gold in treating rheumatoid arthritis and of antimony in treatment of "leishmaniasis" will be discussed further in Section 10.6.
3. Active ligands. Many ligands can be delivered to or from a metal ion in the organism. The classic iron coordination compound, nitroprusside [Fe(CN)5NO]2-, releases NO, which functions as an hypotensive agent causing smooth muscle relaxation. Some selected chelates are presented in Section 10.5.
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