(a) This section applies to insurers and nonprofit health service plans that issue or deliver individual, group, or blanket health insurance policies in the State.

(b) At least 30 days before the change is effective, an entity subject to this section that provides pharmaceutical benefits shall notify in writing all pharmacies under contract with the entity of any of the following changes in the pharmaceutical benefit program rules or requirements:

(1) exclusion of coverage for classes of drugs as specified by the contract;

(2) changes in prior or preauthorization procedures; or

(3) selection of new prescription claims processors.

(c) An entity subject to this section that fails to provide advance notice under subsection (b) of this section shall honor and pay in full any claim under the program rules or requirements that existed before the change for 30 days after the postmarked date of the notice.