Using topical medications while pregnant

  I have a skin condition known as acne rosacea.  The flare ups have gotten worse since I am pregnant (either because of the hormones or because I stopped using my medications when I found out I was pregnant). My dermatologist prescribed Sulfacet-R and Topical erythromycin.  I believe the erythromycin is Pregnancy Cat. B but the Sulfacet is Category C.  
  1. Are these medications fairly safe to use or should I discontinue use until after I give birth?  and
  2. What do the various Pregnancy Categories mean?
Dear Joanne:
Topical medications are usually safe to use during pregnancy. Erthromycin and sulfa,used as topical antibiotic solutions, will not be absorbed in large amounts. Erythromycin can be used without concern. Sulfa is of greatest concern in the last four weeks of pregnancy when it may compete with proteins carrying bilirubin and increased the possibility of jaundice (yellow skin) in the early newborn time.
A Class B drug has no evidence of risk in humans based on studies. A Class C drug has not been tested in humans and risk cannot be excluded. Almost all drugs are Class C.
This information is provided for general medical purposes only and should not be considered a medical consultation. If you have specific questions, please contact your primary physician.