42 CFR § 423.112 - Establishment of prescription drug plan service areas.
(a) Service area for prescription drug plan sponsors. The service area for a prescription drug plan sponsor other than a fallback prescription drug plan sponsor consists of one or more PDP regions as established under paragraphs (b) and (c) of this section.
(b) Establishment of PDP regions -
(2) Relation to MA regions. To the extent practicable, PDP regions are the same as MA regions. CMS may establish PDP regions that are not the same as MA regions if CMS determines that the establishment of these regions improves access to prescription drug plan benefits for Part D eligible individuals.