Rite Aid has expanded an online doctor service for its drugstore customers that is limited to virtual visits but cheaper than a traditional primary care appointment.

The company, the nation’s third-largest drugstore operator with 4,600 U.S. stores, said Friday that its NowClinic Online Care program is available at 58 locations in four cities: Baltimore, Boston, Philadelphia and Pittsburgh. Its rivals, Walgreen and CVS, also run in-store clinic programs. Walgreen operates more than 370 Take Care clinics, while CVS runs more than 600 MinuteClinics.