If you are really serious as pursuing it as a career, you really have to drop economics - no matter how well you done at AS, as it will not be beneficial by the time you study pharmacy. If I were you, you should take chemistry, biology and maths - that way you will be a stronger candidate by the time you apply for unis. Maths be helpful when you do pharmacy as there could be modules where a strong knowledge of maths is helpful. Even if there is no maths involved whatsoever in you uni course, an employer will prefer someone that did maths to the full a level compared with economics.
Anyway, all is not lost, work hard in your A2 year and concentrate on your maths, but also on your biology and chemisty - who knows, you might even get 3 A's with a bonus AS Level in economics.