The percentage of DUI arrests related to prescription and illegal drugs is up even as overall DUI arrests go down in Arizona, an state highway safety official says.

The Governor's Office of Highway Safety says the number of DUI arrests dropped by about 13 percent in 2012 from 2011.

Meanwhile, the number of DUI drug arrests increased by 12 percent, and represented 14 percent of all DUI arrests.

The Arizona Republic reports that office Director Alberto Gutier attributes the increase in drug-related arrests to the availability of prescription drugs such as painkillers.

Gutier also cites synthetic drugs.