This breed is really prone to skin problems. As you have two with the same issue I'd be suspicious of a skin parasite or fungal infection.

It might be something such as contagious mange mites which you can read about here

http://www.marvistavet.com/html/body_sarcoptic_mange.html

Or a skin infection with ringworm

http://www.marvistavet.com/html/body_ringworm.html

or a bacterial skin infection

http://www.e-doc.co.za/modules.php?name=News&file=article&sid=396

Dogs can have contact reactions to products such as rug cleaners, cedar beds, floor cleaners (say pinesol for one), chemicals including lawn chemicals, or even flea bites.

Even if you see no fleas just one bite from a flea can make an allergic dog itch all over so you may want to try using Frontline or Revolution to see if this clears the problem up.

Tick carried diseases can also cause red spotting and an itchy reaction to any infection of the skin can be one result.

If you are not seeing any response to the meds the vet gave you then you should call them to see if they want you to try something else. They should be able to change meds without having to see the dogs again.

Hope this helps you!