Hello, Many drugs can cause a wide range of blood disorders. However, sulfonamide drugs and tetracycline drugs (including doxycycline) seem not to be associated with polycythemia vera. Therefore, theoretically, they are not contraindicated in your case. However, dizziness is a potential, and quite a common side effect of sulfonamides, and therefore if you experience such symptoms, (and you have had it, in the past) then you should not continue to use it. The decision to use doxycycline instead is wise, as both doxycycline and sulfonamides are bacteriostatic drugs but sulfonamides are characterized by high resistance and toxicity rates and therefore their use is being very much reduced lately. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Ervin Toçi