Except as provided for in subsection (b) of this section, the provisions of §§ 15–1623 and 15–1624 of this subtitle apply only to a pharmacy benefits manager that provides pharmacy benefits management services on behalf of a carrier. The provisions of §§ 15–1623 and 15–1624 of this subtitle do not apply to a pharmacy benefits manager when providing pharmacy benefits management services to a purchaser that is affiliated with the pharmacy benefits manager through common ownership within an insurance holding company.