halogenated hydrocarbons (such as chloroform, carbon tetrachloride, tetrachloroethylene and hexachloroethane) were used in a string of continually more efficacious anthelmintics, until their underlying host toxicity was revealed. The modern broad-spectrum anthelmintics were developed by pharmaceutical companies that can afford the screening programs and testing systems that modern drug development involves.

Historically, there have been three main classes of broad-spectrum anthelmintics. These are benzimidazoles, imidazothiazoles/tetrahydropyrimidines,