Just like methods for traditional drug products, the assay and related substances/degradation products methods for single entity combination products need to be proven to be stability indicating.    If the single entity combination product contains a new drug, a forced degradation study will be needed.  If results of the stability of the drug product alone are available, these results should be used to evaluate if the methods are stability indicating.  However, additional degradation experiment on the intact single entity combination product under appropriate conditions will likely be required.  If the single entity combination product contains a generic drug, literature references on the stability of the drug product can similarly be used but degradation experiment on the intact single entity combination product under appropriate conditions will still likely be required.