; or (iii) meets other criteria similar to clauses (i) and (ii) that may be specified by the Secretary; and (B) who prescribes a low volume (as determined by the Secretary) of such drugs to individuals enrolled in plans under this part. In determining low volume under subparagraph (B), the Secretary may determine low volume differently based on the specialty of the applicable physician or practitioner. . (b) Effective date and enforcement delay (1) Effective date The amendment made by subsection (a) shall apply to covered part D drugs prescribed on or after January 1, 2019. (2) Delay in enforcement of enrollment requirement until low volume exemption is implemented The Secretary shall continue not to enforce the enrollment requirement under clauses (ii) through (v) of section 423.120(c)(6) of title 42, Code of Federal Regulations, until section 1860D–4(m), as added by subsection (a), takes effect.