Preserving Access to Orphan Drugs Act of 2018 This bill amends the Patient Protection and Affordable Care Act to expand the definition of orphan drug for purposes of the annual fee paid by brand name prescription drug manufacturers and importers to include medications for rare conditions that were, prior to 2011, approved or in clinical trials. (Drug manufacturers and importers pay an annual fee based on their sales of brand name prescription drugs, excluding sales of orphan drugs.)