A pharmacy provider shall comply with all procedures listed in Regulation .13 of this chapter. A pharmacy provider shall: Upon request, produce records to verify any charge to the CMS Program; and Charge the CMS Program the usual and customary charge to the general public for similar prescriptions. Determination of allowable cost for multiple source drugs designated by the Centers for Medicare and Medicaid Services of the Department of Health and Human Services or for each drug listed in the formulary allowable cost shall be the lowest of the maximum allowable cost. Payment for covered services to a pharmacy shall be made as follows: Payment for formulary drug preparation shall be the: Least expensive available; or Allowable cost according to the State Title XIX Agency; Payment for over-the-counter drugs is not covered except in extenuating circumstances at the discretion of the CMS Program.