When we need medication for our dogs here, we get it from the chemist.
A local vet (there is one near Tarcar Ice Factory just into Calangute area from Candolim area) will usually give a prescription to be filled at a normal chemist.
The International Animal Rescue at Assagao, near our home in Siolim, keep a lot of medications in stock (not for sale) or do the prescription bit.
I am hoping you know exactly what you need, the name (ideally the generic name if possible), mg size of tablet will do. No need to go to a vet, just the chemist.
Your best two local options are "Johnny's" in Calangute main street, nearish to the temple end, or Union Pharmacy in Mapusa, at the start of the main street, market across to your right,its on the corner to your left. If all else fails, the Hindu Pharmacy in Panjim.
Unsurprisingly, most of the medications we give our dogs, are the same as for people but the dosages vary. Also the "Brand" names are different, hence my suggestion of generic names if possible. As far as I am aware, there are very few "pet specific" medications sold here, even the de-worming pills are also for humans (the result of eating local pork!).
Do not be surprised if some of the more "high-tec" drugs are a little expensive, but they should still be cheaper than UK. If available at all!)
If you are having problems getting from "Brand name" to "generic", a Google search often comes up trumps, or books available in the UK easily, give a guide to medicines and drugs and do this conversion. We always travel with a copy as brand names vary from country to country and it can be difficult to find what you need.
If all else fails ( or do it anyway if you want a second opinion/double check) post the list on here and I will go through them.
Good luck
J5
Just been out to the kitchen to check an example for you.
Ostovet, vitamin supplement used in UK for puppies and poorly dogs, Rs54 (well less than a quid} for half a litre! Rock on......

Here are a couple of links that might be helpful. The first is for human-orientated stuff
http://www.drugs.com/
and this one is a pets one
http://www.petplace.com/drug-library/all-drugs-listed-alphabetically/page1.aspx
Hope they prove useful
J5

Most medicine come with so much of one ingredient and so much of another so
bring the leaflet or the box that comes with your medicine if it list the ingredients and dosage , Johnny has a book that lists local medicine with same ingredients and dosage or he will give you two lots if he can't match the dosage in one medicine

If you are buying a lot try sending some home some via "sign for post", to stop you going over weight

Me

Thanks for your help. I will bring the animal meds with me when I go to Goa in April and hopefully will get sorted out. Noticed one of my cats has a sore eye today, so back to the vet again....
Gail