Police have conducted drug sweeps of the city’s two high schools for the first time in five years. Four drug-sniffing dogs and their handlers conducted the sweeps while classes were in session. The dogs searched lockers, common areas, and restrooms at Nashua High School North and Nashua High School South, but did not search classrooms or students’ backpacks. No drugs were found at either school. The searches were described by school officials as a preventive measure rather than a response to any rise in drug use.