All drugs that should not be taken by people allergic to sulfa drugs will so state in the information sheet under "contraindications", warnings, etc.
Or you can always ask the pharmacist. They can tell you.
And premarin does not have sulfa in it. The class of drugs known as "sulfa drugs" are antibiotics. Some other drugs have similar chemical make up and may cause the same side effects that a sulfa antibiotic might...nausea, upset stomach, etc.