When Hoshi Sato and Trip Tucker caught a strain of a silicon-based virus in 2154, Phlox ordered them to use sonambutril after Sato was able to escape confinement. The sedative was able to knock out both officers for a long period of time. (ENT: "Observer Effect")
The name draws from word somnambulant, meaning to sleep walk. It may also draw from the name of the real world Nembutol, a barbiturate sedative sometimes used in the late 20th century to induce sleep.