How is zakat on medicines in a pharmacy paid? Is it based on their new price or old price, after their prices increased months ago?

A merchant must appraise all his commercial goods at their current market value upon the completion of a year (hawl). To this, collectible debts are added, and due debts owed by him are subtracted. Then, Zakat is to be paid at a rate of 2.5% if the total reaches the Nisab of gold (85 grams). Fixed assets used [for business] are not subject to Zakat.