Md. Code, Insurance § 15–1631

Except for an overpayment as defined in § 15–1629(h) of this subtitle, if a claim has been approved by a pharmacy benefits manager through adjudication, the pharmacy benefits manager may not retroactively deny or modify reimbursement to a pharmacy or pharmacist for the approved claim unless:

(1) the claim was fraudulent;

(2) the pharmacy or pharmacist had been reimbursed for the claim previously; or

(3) the services reimbursed were not rendered by the pharmacy or pharmacist.