1) Absence of Target (Ergosterol's absent)

2) Alterations in Target (Pen. Binding Protein Alterations)

3) Low concentration at target (Interference with membrane passage)

4) Lack of metabolic activation (Antifungal Flucytosine -> Fluorouracil)

5) Inactivation (Penicillinases)

6) Escape from Effect (Alternate Metabolic Pathways)