In reply to zak:
I've bought antibiotics in Pakistan, in Karimabad, which is not where you're going but it means getting them in Islamabad is no problem. There is at least one decent pharmacy at the area known as 'Super Market', where all the decent shops are. I bought Cipro and Flagyl and they were ridiculously cheap. They had Urdu script on one side and english on the other. Most pharmacists will speak at least a bit of english anyway.
But as someone said, if it is a properly organised commercial trek then they will have a very good first aid kit with this stuff in it - and more I would hope. But it doesn't hurt to have a few bits and pieces on yourself just in case, particularly decent painkillers, ibuprofen or stronger (Nurofen Plus etc).
If you were doing the Baltoro trek (which I have not done) then you have plenty of time to acclimatise and certainly shouldn't need Diamox. But going in over the Gondo La (la means pass, so don't say La Pass, it's like saying you're going to the pub pub) has a more intense height gain, so it depends on your itinerary. Most commercial operations rush their trips, though they swear blind otherwise, so it is wise to have a good think about AMS for this trek.
D