How is a pharmacy's merchandise zakat calculated: by its retail price or its current wholesale price?

The zakat on trade goods is calculated by appraising them at the end of the Islamic year (Hawl), and a quarter of one-tenth (2.5%) of their value is to be paid, regardless of their purchase price. If the merchant sells retail, the goods are appraised at the retail selling price. However, if they sell wholesale, they are appraised at the wholesale price.