The county will allow pharmacies that register with its Department of Health Services to sell syringes over-the-counter in an attempt to slow the spread of HIV and other infections that can be transmitted through needles shared by drug users. The Board of Supervisors voted 3-2 on Tuesday to allow pharmacies to sell up to 10 syringes to customers without a prescription, a move made possible by the passage of a January ballot measure that allows cities and counties to authorize the sales. The county hopes to begin the sales by October.