§ 13-o. Pharmaceutical fee schedule. The chair shall adopt a pharmaceutical fee schedule which shall establish maximum allowable fees for prescription medicines provided pursuant to this chapter. The schedule shall include a single dispensing fee. Nothing in the fee schedule shall preclude mail order supply of scheduled medicines, provided that the fees for such mail ordered medicines do not exceed the costs provided by such fee schedule. Any pharmacy providing prescription medicines shall provide the generic drug equivalent, if a generic equivalent is available, unless the prescribing physician specifically provides otherwise by prescription. The fee schedule may be modified on each succeeding April first, provided, however, that usual and customary fees may be charged for drugs that are not included in a then-current fee schedule, but are approved for use by the chair.