I think you can approach to the problem by specifying segments. I think this would be a good approach:
1) Segment 1: Aspirin users for fever
2) Segment 2: Asprin users for heart attack
Your segment 1 can be calculated as following:
Number of users: Pop. of Germany * avg people who will be sick in a year * percantage of patient that can/ want to you use aspirin * how many time they are being sick in avg * how many package they will use per time in avg
1) Market share of Bayer * total number * price of buyer
2) Market share of the others * total number * avg price of others
For segment 2:
Pop of germany divided to 4 age group with respect to life expectancy and multiply each population group with a reasonable probabiliy for heart attack. this would be a total potential population under the risk of heart attack = Potential group
Potential group * percentage of people willing to use/ could use asprin= Total market for Segment B.
Pricing: Same as the segment 1
So, this would be my approach. I hope this will help.