Clinical Drug Experience Knowledgebase

Thimerosal is organomercury antiseptic and antifungal agent, used as a preservative in vaccines, immuloglobulins, nasal sprays, contact lens solutions. In USA, European Union countries thiomersal is no longer used in childhood vaccines due to public fears, although the FDA review of 1999 foud no evidence of harm from the use of thimerosal as a vaccine preservative, other than local hypersensitivity reactions. Thimerosal was used as a component of topical antiseptic solution and antiseptic ointment for treating cuts, nasal sprays, eye solutions, vaginal spermicides, diaper rash treatments, but re-evaluation of the drug in 1980-s demonstrated ineffectiveness and toxicity in topical pharmaceutical products, and topical thimerosal was withdrawn from the market. The mechanism of action of thimerosal has not been fully elucidated. It is believed that thimerosal inhibits sulfhydryl-containing active site of various enzymes and binds to sulfhydryl compounds, such as glutathione, cysteine, and SH groups of protein. In addition, thimerosal activates the InsP3 calcium channel on endoplasmic reticular membrane, thereby triggering the release of calcium from intracellular stores resulting in a calcium-induced calcium-influx of extracellular calcium. Consequently, thimerosal may induce or inhibit cellular functions dependent on calcium signaling.   ^NCATS