I use Seretide. It's not universally available over the counter. In my Isaan province I have a tame pharmacist who will supply it though in Khon Kaen, a neighbouring province, it's not available in the pharmacies that I have tried. It's available in Pattaya (as are most things!) but not everywhere. When I first came to Thailand Boots used to supply it over the counter in Pattaya but that stopped some time ago.